by Richard Lunsford (drrich2) 2-14-05
with special thanks to Robert MacCargar
for  a great deal of information & editorial assistance.

I.) Introduction.

            Concerned about proper lighting for your pets? Maybe you’ve heard of ‘UV-B’ that some claim turtles need, some say should have, & some say doesn’t matter if fed a good brand-name food (i.e.: ReptoMin or Mazuri). How is it connected to Vitamin D3? How can a light give you vitamins? Can you just use those T-Rex ‘Solar Drops’ you spotted at PetsMart the other day? Do turtles need UV-B lighting? 

If so, is the ZooMed ReptiSun 5.0 (or 10.0) the end-all/be-all of UV-B fluorescent light bulbs, or is the ReptiGlo 8.0 okay? Will those 7% ‘desert’ fluorescent bulbs hurt your turtle? If you have a UV-B fluorescent bulb, why do you need a separate heat basking bulb? What about these mercury vapor (a.k.a. ‘UV-heat’) bulbs that purport to replace both your UV-B fluorescent & basking heat bulb by producing higher UV-B output than a fluorescent and also heat? Are the ZooMed PowerSun and T-Rex Active UV-Heat the only two worth considering, or do competitors like Big Apple’s Capture-The-Sun offer a better deal? And what about this fairly new bulb, the ‘Mega-Ray’ that many higher-end keepers endorse as top-of-the-line? Should you pay more money for the externally-ballasted version of the Mega-Ray? 

            It’s a complex topic, so let’s hit it step-by-step & link resources for more info.


II.) What Is UV-B?


            UV stands for Ultraviolet light, a range of light wavelengths (which we perceive as ‘colors’) outside the range the human eye can see. Ultraviolet light is invisible to us, but is seen by some animals (including bumblebees, birds, lizards & we think turtles). UV light is subdivided into UV-A, UV-B & UV-C. Light (ultraviolet & otherwise) is part of a range of radiation we call electromagnetic radiation (see Appendix III for more on electromagnetic radiation). 

            You & I can’t see into the ultraviolet light range, but some animals can (we think UV-A is most important). Some reptiles can see UV-A light, and might behave more naturally with it. After all, the mix of light wavelengths (colors) you can see determines how things look to you. If a ‘color’ you normally see is missing from the lighting, the colors of objects look different. Since you can’t see ultraviolet light, an object may look the same color to you indoors (no UV lighting) or outdoors (sunlight contains a lot of UV-A light), but very different to the Bumble Bee or your iguana! (Robert MacCargar’s Russian Tortoises displayed mating behavior after switching from a halogen bulb to a Mega-Ray; the latter produces plenty of UV-A & we think that’s why). 

            Note: Humans (in a really small study) were found to strongly prefer tanning beds that offered UV light, even though they couldn’t see it (Tanning Beds Obsession or Addiction)! There are reports of some pet lizard species showing a preference for basking in enclosure areas with certain amounts of UV-B.


            Ultraviolet light (UV) is electromagnetic radiation in the wavelength range of   that is invisible to the human eye. Its intensity is measured microwatts/ centimeter2 (µW/cm2). 

            Ultraviolet light (UV) is broken down into 3 sub-categories (a.k.a.: spectrums) by wavelength:


1.)    UV-A: 320 – 400 nm. This UV range is not thought to impact calcium metabolism in the body, but some reptiles can see into it so things may look more natural or ‘normal’ to them if you provide it. Most UV light in sunlight is UV-A.

2.)    UV-B: 290 – 320 nm. This UV range provides the light that converts a precursor into Vitamin D3 in the skin, both of your turtle & yourself! It also causes sunburn. What’s more, we’ve learned there is a sub-set of this range, called D UV-B (a.k.a. ‘creative’ UV-B17), thought to provide most of the Vit. D3 conversion in our pets. We’ve recently learned some higher UV-B wavelengths are destructive rather than creative17.* Warning: our understanding of such matters is often based on research with animals other than turtles. We tend to ‘assume’ the same basic theory holds true for turtles.

3.)    UV-C: 200 – 290 nm. This UV range is usually screened out by our atmosphere (especially ozone) & we are not exposed to it in natural sunlight (high altitudes may vary). It can damage DNA, cause blindness, & is used in UV-Sterilizers, which use a UV-C bulb inside a closed container (to protect you from it) to sterilize aquarium water passing through it.

* - To learn more about creative & destructive UV, see the Jukka study & follow-up discussion between Jukka & MacCargar.


III.) So What is Vitamin D3 & What’s it got to do with UV-B?


Vitamin D3 (a.k.a. Cholecalciferol) is a fat-soluable vitamin required by the body (your turtle’s & yours) to properly absorb calcium via the intestine (it also affects bone deposition & reabsorption12). A lot of calcium is stored in our bones, which not only provide our bodies structural support/integrity, but also serve as calcium store houses – calcium is deposited in & removed from bone over time. If an animal has insufficient calcium in the diet, or lacks enough Vitamin D3 in the body to absorb it, the body will perceive that there’s not enough calcium in the blood & release parathyroid hormone which then moves calcium from the bones into the blood. (Understand: calcium is involved in muscle contractions & other roles in the body besides strengthening bones. If your body thinks you’re short on calcium, it’ll take it from your bones!). (Note: Vit. D3 is not the final active form in the Vitamin D series, but it’s a key step; read Melissa Kaplan’s article9 for specifics if interested). Technical Note: UV-B doesn’t directly ‘make’ Vit. D3; it converts 7-dehydrocholesterol (pro D3) to previtamin D3, which is then thermally isomerized to Vit. D314,15,16

Either Chronic Vit. D3 or calcium deficiency can lead to Metabolic Bone Disease (MBD; Secondary Nutritional Hyperparathyoidism is the type we’re interested in). In turtles, this can weaken & deform the skeleton & soften & disfigure the shell. Such damage can be permanent. There are different manifestations of MBD (covered in more depth in this article9 by Melissa Kaplan, where she discusses Osteoporosis, Osteomalacia, Rickets & Fibrous Osteodystropy - there’s overlap amongst these).

Rather than recap her discussions, here’s a simplified version:

1.)    Chronic Vit. D3 deficiency leads to poor calcium absorption in the gut.

2.)    This causes low calcium levels in the blood.

3.)    The body (in response) produces more parathyroid hormone.

4.)    Parathyroid hormone causes removal of calcium from bone into the blood (to maintain important functions like muscle contractions, including heart muscle!).

5.)    The bones are weakened 2 ways; they don’t get enough calcium added (due to deficiency), & some of the calcium already in bone is removed (to compensate elsewhere). In turtles, the shell may greatly soften.

6.)    The reptile body tries to compensate in varied ways (i.e.: thickening high-stress areas, build up of connective tissue, etc…) which can lead to deformity & impaired functioning (i.e.: inability to eat due to soft, bowed jaw bones). 

Hatchling turtles start with soft shells which should firm up the first few months of life. This requires calcium. They (& their skeletons) are growing & that takes calcium. Calcium-deficient older turtles can develop soft shell. If severe the shell may feel almost spongy. In turtles, unlike other reptiles, we often examine the shell first when suspecting calcium or Vit. D3 deficiency. 

            Vit. D3 overdose can also be harmful. In this Tortoise Trust Article11 A.C. Highfield states it may cause mineralization of soft tissues and kidney damage.


            Your turtle gets Vitamin D3 from 2 sources:

1.)    UV-B Light (in nature provided by sunlight) converting a dietary precursor to the active form. This is especially critical in herbivores. Vitamin D3 production via UV-B acting on a precursor is self-limited; the animal cannot overdose on Vit. D3 via UV-B exposure! Melissa Kaplan9 cites research13 in stating “Vitamin D3 is best obtained through regular exposure to ultraviolet radiation; in studies of iguanas [Bernard et al.], those iguanas receiving Vitamin D3 injections or diet supplements fared less well than those iguanas whose main source of D3 was from ultraviolet radiation.”

2.)    Dietary Vit. D3, which is found in good brand name commercial foods & some carnivorous food items (it is said to be concentrated in the vertebrate liver). Vit. D3 is, for our purposes, practically absent from herbivorous fare so strict herbivores (i.e.: most tortoises) are very vulnerable to MBD (plants produce a precursor but UV-B is necessary to convert it for D3). This is why so many people encourage you to put vitamin powders with Vit. D3 on your pets’ food. Note: You can overdose dietary Vit. D3! Don’t overdo supplements! Read this Vet. Article12 for the frightening effects. 

Humans live indoors under artificial lighting producing no UV-B, but in their brief forays outdoors (to & from the car, work, the mall, mowing the yard, etc…) they catch enough UV-B from natural sunlight to supplement dietary Vit. D3 & avoid MBD. Over the decades legions of reptiles have suffered & died because owners didn’t know they were dying, sealed away in UV-B-proof glass aquariums with regular fluorescent or incandescent light bulbs providing no UV-B. Don’t assume enough sunlight for you is enough for your pet; animals vary widely in amount of body exposure & sensitivity to UV-B (i.e.: diurnal desert lizards may need more than a forest-dwelling chameleon).


IV.) Does Your Turtle Need UV-B?


            Yes & no. Your turtle has to have Vitamin D3 to live. A turtle receiving adequate dietary Vit. D3 should not suffer MBD even with no UV-B lighting. That said, we’ve seen ads claiming bearded dragons under good UV-B lighting grow a good deal faster than those without, it’s said to’ve turned at least one chameleon in dismal health around & there’re reports of stimulated appetite & sexual behavior. UV-B bulbs typically also produce UV-A which may make colors more natural to reptiles who see into the UV-A range. Do things look different to your turtle under a UV-B bulb? Probably! There are reputable reports of increased mating behavior using the Mega-Ray bulb, which produces plenty of UV-A & B. Note: Most UV in nature is UV-A. ‘Basking’ bulbs marketed as producing UV-A don’t produce UV-B (unless they specifically claim to), but UV-B bulbs do produce UV-A!  

We’re still learning the full benefits of natural sunlight; Robert MacCargar noted the sun’s UV light has antibacterial & anti-fungal properties, & turtles may bask to dry out (alternate submersion & drying out makes the body surface hostile to parasites & disease-causing germs), warm up & get UV. It’s believed UV-B conversion to Vit. D3 occurs in the skin of turtles, not the shell – this may play a role in the ‘legging’ maneuver (sticking the back legs outward; on TF termed the ‘Superman pose’). This matters because unlike other reptiles turtles can drastically cut their UV-B exposure just by pulling into their shells (a built-in beach umbrella!), although the shade is so narrow that under strong UV-B bulbs (i.e.: the Mega-Ray) there can still be high exposure. 

            Strict or strongly herbivorous turtles (i.e.: Greek, Russian, Egyptian, Hermans & Sulcata tortoises) get little dietary Vit. D3 naturally & you’ve got to give them UV-B lighting &/or dietary Vit. D3 supplementation or they will die. In Practical Encyclopedia of Keeping and Breeding Tortoises and Freshwater Turtles8 page 90, A.C. Highfield described an experiment he & colleagues undertook comparing tortoises reared under mostly incandescent lighting with calcium & Vit. D3 supplements (who did well) and those reared under extensive UV and full spectrum exposure & calcium but not D3 supplements (who got symptomatic later; this was traced to the reduced UV production of such bulbs as they age). It’s been said some snakes don’t need UV-B lighting because their dietary intake is adequate (strict carnivores taking whole prey often vertebrate items). It’s said Vit. D3 is concentrated in the vertebrate liver. I don’t have a source for what those levels are, or what levels occur in common feeder invertebrates. 

            How well a ‘natural’ diet meets the needs of omnivorous turtles is hard to judge. Many popular pet turtles feed mainly on invertebrates (i.e.: insects & insect larvae, snails, etc…) in the wild rather than vertebrates (i.e.: fish, rodents & birds), & it’s hard to judge whether Vit. D3 is sufficient alone unless you observe signs of MBD (& who wants to let that happen)? The main vertebrate prey item for captive turtles is fish, & some fish contain thiaminase (a heavy fish diet with such species can be dangerous; here’s an article to learn more). Turtles getting only a natural diet & kept outdoors are getting plenty of UV-B & if the diet is otherwise wholesome/nutritious they should have no problems. An indoor omnivorous or carnivorous turtle on a solely natural diet should get UV-B lighting just in case dietary Vit. D3 isn’t enough (my recommendation until proven otherwise). 

            The case for indoor turtles fed natural foods with Vit. D3 supplements like Rep-Cal, &/or fed Vit. D3-supplemented commercial turtle foods (like ReptoMin & Mazuri Aquatic Turtle Foods) isn’t clear. You can certainly argue that UV-B lighting is unnecessary & expensive under these conditions. You can keep your animals this way guilt-free, as they will likely be healthy. I recommend UV-B lighting for most turtles reasonably expected to encounter & benefit from it in Nature (for potential psychological benefits from UV-A as well as Vit. D3). 

            Special Note: There is a concentrated liquid Vit. D3 product called Solar Drops, marketed by T-Rex (under Reptile Products, the T-Rex Bone Aide Series). To make a long story short, I don’t recommend using the product. This is a controversial issue, & I recommend you read our Advanced Herpers’ thread on the subject

            Exceptions: Advanced TF Member & ITTN Affiliate Site Owner Scott Thomson opined that Fly River turtles are, for practical purposes, exclusively aquatic (do not bask) & given UV-B’s poor penetration of water & the modest UV-B output of most commercial bulbs, it’s not likely useful to provide them UV-B lighting. One could argue much the same of alligator snappers. Be warned some North American species reputed to be strict aquatics who don’t bask (i.e.: stinkpots, common snappers, softshells) do bask fairly often (basking shots of these litter TF’s Field Herping forum section), & natural sunlight UV-B production is so high it may penetrate enough to aid them when they surface for air or enter shallow water. So don’t write them off for UV-B lighting until you know if yours basks in captivity. Note: Robert MacCargar knew of a 1 year old alligator snapper that started basking & had restored appetite under a Mega-Ray bulb.


V.) Can UV-B Penetrate Things Other Than Air?


            Yes & no. UV-B does not penetrate glass or acrylic well at all; direct sunlight striking a single window pane (producing over 200 microwatts/ centimeter2) may send weak UV-B through. This is very important because smaller aquariums (i.e.: 20 gallon long) are often sold with hoods that put a glass plate (a.k.a. ‘splash guard’) between the enclosed fluorescent light bulb & the water. This glass plate will prevent enough UV-B from a UV-B fluorescent bulb (i.e.: ReptiSun 5.0) from reaching your turtle unless removed.


            Before you remove a glass plate splash guard from a tank hood, be warned:


1.)    They are ‘glued’ in very tightly & hard to remove.

2.)    Even smashing the glass out with a hammer will be an ordeal.

3.)    Wear strong eye protection (goggles) & cover the glass surface you’re striking with a cloth to reduce risk of flying glass slivers getting on or around you.

4.)    Do it outdoors or you’ll be picking glass out of your feet off & on for months.

5.)    Do it at your own risk – smashing glass is not entirely safe whatever you do.

6.)    Fluorescent bulbs are much cooler than incandescents so the risk of the bulb shattering if water is splashed on it is much less (in my experience), but what risk there be is risk you take.


UV-B will be ‘screened out’ (no pun intended) to some extent by mesh products like screen lids on aquariums. The finer the mesh, the less UV-B gets through.


            Strong UV-B does penetrate into the upper few inches of water but the intensity falls off rapidly. For our purposes, we’ll assume the vast majority of UV-B your turtle gets is obtained via basking, and that brief exposure swimming at the surface or coming up for air is fairly inconsequential.


VI.) Learning From Nature: How Much UV-B is there in Sunlight?

             God put a great big UV-B bulb in the sky to shine on most of us about 12 hours per day; it’s called the Sun. This fusion-based thermonuclear fireball is nearly 110 times the diameter (> 1 million times the volume) of the Earth & ~ 93 million miles from us. Even at that distance the radiation output is phenomenal & were it not for our atmosphere (& particularly ozone) the UV-C component would kill us all. 

            When you stand outdoors a few feet into the shade on a bright, clear sunny day around noon, you’re getting bombarded with way more UV-B than popular fluorescent UV-B bulbs like ReptiSun 5.0, ReptiGlo 8.0 &, yes, those ‘Desert UV-B’ fluorescent bulbs put out. You may get UV-B roughly comparable to basking ~ 1 foot under some mainstream mercury vapor flood bulbs like the ZooMed PowerSun; maybe 50 µW/cm2. So you can (as of this writing 2-14-05)  pretty much quit worrying that a ReptiSun 5.0, ReptiGlo 8.0 or, oh my, a desert fluorescent bulb will roast your turtle with deadly intense UV-B rays. Be cautious, check it out, but them’s the facts. (Note: The ReptiSun 10.0 produces a higher percentage UV-B than the 5.0, & certain types of reflectors can nearly double effective output. If you use paired bulbs &/or reflectors that enhance UV-B radience (polished aluminum & deep dome brushed aluminum reflectors do; white porcelain doesn't) at close range (under a foot), you need to check what UV-B output the turtle is getting).

            On a clear day if you look straight up at the noonday sun, it’s instantly blinding. If you don’t stop fast you’ll get eye damage that can get permanent. But you & a date can watch a romantic sunset for several minutes hardly blinking. Sunlight is heavily screened by our atmosphere (including screening out UV-C) before it reaches us, & output varies radically over the course of the day. 

            UV Radiation output peaks around noon, and about 20-30% of the total daily UV Radiation a point on Earth gets comes between 11 a.m. & 1 p.m., & about 75% between 9 a.m. & 3 p.m.2 The same source states in temperate regions biologically damaging UV Radiation hitting the surface shows strong seasonal dependence (with much less variation as you get nearer the equator). UV Radiation varies somewhat with altitude & can be decreased by cloud cover. Noon levels are the point of high intensity UV-B output some use as a standard to judge how much UV-B our reptiles should get. This is a bad mistake. Consider:


1.)    Just because a reptile basks doesn’t mean it does so at high noon. Some quit basking & do other things before then.

2.)    Even if a reptile basks at noon, it could at most get roughly that intensity level for a couple of hours. Your UV-B bulb will be on all day.

3.)    Your reptile may bask with other considerations in mind (i.e.: a desire to warm up & improve mobility). It’s adapted to deal with the sun in its native habitat, not some wannabe bulb in your man-made enclosure.

4.)    Many reptiles (i.e.: Iguanas in the tropics, or an Eastern box turtle on a forest floor) in nature live in or under forest canopies with a lot of shade. Even the shade may offer plenty of UV-B in some habitats, but it’s not high-noon intensity.

5.)    Just because a wild reptile is periodically exposed to high levels of UV-B doesn’t mean it requires nearly that much to make the Vit. D3 it needs to prosper.


VII.) General Principles of UV-B Lighting.


Since UV-B doesn’t pass through normal glass, UV-B bulbs are made from special materials that allow transmission of UV-B light. Therefore, UV-B lighting is expensive & bulbs must be replaced from time-to-time. Decay rates vary across products & brands, & even within a line (i.e.: 2 ZooMed PowerSun 160 watt Floods won’t necessarily decay at the same rate). Robert MacCargar recommends changing UV-B bulbs (fluorescent or mercury vapor) every 6 months or a Mega-Ray annually unless you have a light meter (to confirm continued good performance). While the Solarmeter 6.2 page states “Lamps should be replaced when output drops to about 70% of their original (new) readings,” MacCargar said that was regarding sun tan lamps & where reptile bulbs are concerned % & degree of change mean nothing; only current UV-B production in µW/cm2 matters.

Only bulbs advertised as producing UV-B provide meaningful amounts. The ‘basking bulbs’ sold at pet stores for around $10-20 are not UV-B bulbs (although some produce UV-A). Note: Bulbs marketed as ‘Full-Spectrum’ do not produce significant UV-B unless they specifically advertise on the package that they produce UV-B! ‘Full-Spectrum’ does not = UV-B.

Rober MacCargar noted quality UV-B production is important because some UV light is actually destructive of the Vit. D3 synthesis – depending on a bulb’s output of beneficial vs. destructive UV, a bulb producing less total UV-B could be better than a competitor with higher output but a poor distribution.

A word about UV-B %’s: when a ReptiSun 5.0 says it produces 5% UV-B, or a ReptiGlo 8.0 says it produces 8% UV-B, what they’re talking about is what percentage of total iridescence emitted is UV-B. Since a ReptiSun 5.0 & a ReptiGlo 8.0 probably don’t produce exactly the same amounts of total iridscence, you can’t assume that 8% of a ReptiGlo 8.0’s output is greater than 5% of a ReptiSun 5.0’s. You also can’t assume the spectrum range of one is as good as the other. So don’t be fooled into direct comparisons. However, bulbs in a given brand line sold as being lower UV-B (i.e.: ReptiSun 2.0 instead of 5.0) can be assumed to produce lower amounts of UV-B & I don’t recommend them for turtles.


VIII.) Types of Lighting.


            There are 2 main types of lighting: Fluorescent Bulbs (mostly traditional tube bulbs, but there are coiled compacts that screw into standard lamp sockets); fluorescents produce light but little heat) & Incandescent (which produce heat & light; mercury vapor bulbs are one type). Examples of tube fluorescents include the ReptiSun 5.0 & ReptiGlo 8.0, of coil fluorescents the new ReptiSun 10.0 compact, & mercury vapor incandescents the T-Rex Active UV-Heat, ZooMed PowerSun & Reptile UV Mega-Ray.


            1.) Fluorescent – long narrow glass tubes filled with gas that fluoresces when an electric current is passed through it. They give out a lot of light & relatively little heat (many are uncomfortably warm/hot to the touch). At a hardware store you’ll see 20 watt coiled fluorescents said to produce as much light as a regular (a.k.a. incandescent) 60 watt bulb. They may produce ~ as much light, but not nearly as much heat.

Fluorescents gave us our first UV-B bulbs, starting with the (really low output) Vita-Lite. Now the strongest brand name UV-B fluorescent on the market is the ReptiSun 5.0, & its identical twin the Iguana Light 5.0. A contender is the ReptiGlo 8.0. ZooMed is producing ReptiSun 5.0 & 10.0 ‘compacts’ (coiled fluorescents that screw into a standard incandescent lamp fixture) to put right over a basking platform – pretty new but the 10.0 supposedly puts out much stronger UV-B than tube bulbs.

            The best UV-B Fluorescents produce consistent UV-B intensity that gradually decreases over time. They give more creative & less destructive UV. While they produce much less UV-B & heat than reputable UV-B mercury vapor bulbs, they are more dependable & predictable for those without UV-B light meters. Consider using a hood with a reflector for tubes; it can nearly double their UV-B production.

            Bottom Line: The ReptiSun 5.0 is a reputable time-tested product expected to consistently produce adequate UV-B at close range over the basking area for turtles who bask under it. Regarding the UV-B spectrum range produced (‘good’ or ‘creative’ UV-B vs. destructive UV-B), Robert MacCargar states the ZooMed fluorescents are excellent! They don’t produce as much UV-B as mercury vapor competitors initially do (or as much as we’d prefer) & you’ll need another bulb or ceramic heat emitter for heat. ‘Desert’ UV-B fluorescents, despite the name, don’t produce enough total UV-B to be worrisome can be used. The 5.0 & 10.0 compact ReptiSuns are new ones to watch; the 10.0 tube bulb looks light purple when glowing & the light isn't to some peoples' taste. I recommend the ReptiSun 5.0 tube fluorescent bulb & keep an eye on the 10.0 coil & tube versions, which may be a better choice for some.


            2.) IncandescentStereotype: the classic G.E. light bulb. A metal filament inside the bulb glows brightly when an electrical current passes through it. Incandescent bulbs come in a variety of shapes & sizes, but I’ve never seen one with the very long, narrow form-factor of the stereotypical fluorescent bulb. They produce decent light for viewing & reading, but less than fluorescents. Incandescents produce strong heat, & touching one can burn you badly. Most don’t produce UV-B, but special incandescents called mercury vapor bulbs can be designed that do.


            3.) Mercury Vapor (Non-Mega-Ray) – A modified incandescent producing heat and light. If the bulb is made out of special glass that allows UV-B transmission that bulb can act as both a UV-B source & a heat basking bulb. Examples are the old-style T-Rex Active UV-Heat* and ZooMed PowerSun bulbs. They initially produce much more UV-B than tube fluorescents, but have more drastic drop-off. Contrary to claims they have 'hot spots’ (don't produce a constant, even field of UV-B (I'm talking flood versions), Robert MacCargar reported the old-style T-Rex Active UV-Heat* & ZooMed PowerSun bulbs he’s tested were very consistent; your mileage may vary with other brands). Due to heat production, it’s recommended they be used in ceramic socket lamps (plenty of 250 watt ceramic basking lamp fixtures are on the market). The cheap ‘clamp lamps’ at Wal-mart aren’t recommended! Dimmers don’t work with mercury vapor bulbs but timers are okay.

    * Those T-Rex bulbs were the 'old style' before T-Rex switched to the manufacturing process also used to produce the Mega-Ray bulb.

            Spot vs. Flood – Mercury Vapor UV-B bulbs come in 2 main forms; the flood version (which produces moderate UV-B over a wider area) & the spot version (which produces an intense area of UV-B in a small area, & is placed much further from the animal). For most turtle enclosures I recommend only using flood versions.

            Both the PowerSun & Active UV-Heat bulbs are self-ballasted; this has pros & one major con. Self-ballasted bulbs screw into the ceramic fixtures mentioned above, & the setup is initially cheaper. But they’re fragile & prone to die, especially if jostled while hot. It’s my impression they have a fairly high fail rate, and you’ll often see these sold with pro-rated warrantees (i.e.: the warrantee value decreases with the age of the bulb, so if it fails after 3 months, they won’t refund the full price!).

            Robert MacCargar of the Yahoo! Discussion Group for UV-B Light Meter Owners made a posting to the group 1-28-04 Re: Mercury Vapor bulbs (Note: the Mega-Ray wasn’t out yet, but T-Rex Active UV-Heat (old style)* & ZooMed PowerSuns were). He discussed why self-ballasted bulbs have a shorter lifespan, & stated MV lamps used for reptile applications have an AVERAGE life of 6 months. Some will last shorter, some longer, but with the combined study of over 400 lamps, 6 months is the average.” (He discussed the role of vibration in failure; sturdy fixed positioning helps). Regarding UV-B output decay over time, he stated “Mercury Vapor bulbs will decay on the AVERAGE of 70%. Some will decay less and some will decay more. Simple terms, a 160wt SBMV FLOOD lamp that starts at 80uW/cm2@12 will decay (on the average) of 64uW/cm2 giving you 16uW/cm2@12”. Most of the decay happens very quickly in the first few days. It then levels off over the next several months.” MacCargar later states “MV bulbs produce 3 times more UVB in the 290-300 (D-UV) nanometer range than “tube” type UVB bulbs of the total UVB out-put. 10uW/cm2@12’ from a MV FLOOD lamp is equivalent to 30uW/cm2 from a tube lamp. This fact helps explain why every rehabilitator I have spoken to sees a remarkable difference in the effects of MV lamps over tubes even though they may be using MV FLOOD lamps that are only emitting 10-15uW/cm2. (I still recommend using ZooMed 5.0 tubes with MV Flood style lamps).” MacCargar told me the ‘3x’s D-UV-B with mercury vapors vs. fluorescents’ rule doesn’t always hold true; it varies with brand & product line.

            Bottom Line: The PowerSun & Active UV-Heat mercury vapor flood versions produce good heat & UV-B when used about a foot from the basking platform, superior to a fluorescent in UV-B intensity with no separate heat bulb required. They may excel at producing D-UV-B, the sub-range of the UV-B spectrum thought most beneficial for Vit. D3 synthesis in reptiles. But they’re often a tad more expensive & the thing may up & break on you for little or no reason. Note: The newer style T-Rex 100 watt Flood bulbs made by Westron using the design for Mega-Rays produce much more UV-B than the 'old style' T-Rex Active UV-Heat bulbs so don't use closer than 12" from the animal. To watch for further developments in the T-Rex Active UV-Heat flood mercury line, check UV Guide's site often.


            4.) Mega-Ray – The hands-down favorite of much of the very knowledgeable membership of the Yahoo! Discussion Group for UV-B Light Meter Owners, the Mega-Ray offers drastically higher UV-B output than older competitors & a reputation for quality & dependability (some competitor products have a reputation for inconsistent output, in some cases dangerously high!). They have a much better output decay rate than older mercury vapor bulbs. Mega-Rays are ‘narrow flood’ bulbs; more focused than competitor floods but much broader than spots. The 60 watt version produces relatively little heat, & due to their UV-B intensity any Mega-Ray may be kept far enough from the basking platform that your turtles may need a separate heat lamp. On the other hand, the 100 watt version produces heat at around 1.5+ feet. They offer Self-Ballasted & Externally-Ballasted products; with the latter you pay more up front for a more reliable product over time (I recommend the externally-ballasted version of the Mega-Ray).

            Reptile UV states of their 100 watt self-ballasted flood Mega-Ray bulb “Mega-Ray SB 100-watt narrow-flood all-in-one is a 100-watt SB Par-38 True Frosted Flood Lamp. A true flood lamp it will disperse usable UVB in a 30” circumference at a 20” distance. This bulb is warranted for 6-months to produce a minimum of 50 microwatts (mW/cm2) at 12”.” (The externally-ballasted version has the same warranty for a year! These are not pro-rated!). The specifications they give for the bulb are “MINIMUM distance+ setting of 12” will produce approximately 250-350 microwatts (mW/cm2).
MAXIMUM distance+ setting of 20” will produce 100-150 microwatts (mW/cm2).” (Note: I expect you’ll get well more than 50 mW/cm2 @ 6 months!).

Understand: the Mega-Ray produces a lot of UV-B. Much more than PowerSun or Active UV-Heat flood bulbs, & should maintain high production much longer. So much that you won’t put one 1 foot from your basking platform 12 hours per day. The 60 watt version won’t double as a sole heat bulb, a major selling point of some other mercury vapor bulbs, but the 100 watt can.

            Learn more about the Mega-Ray at Reptile UV, the company that’s marketing them (others are selling them, too). There’s a wealth of information at this site.

            Bottom Line: For enclosures with the bulb about a foot or less from the animal, I don’t recommend the Mega-Ray. For a lamp suspended over a large enclosure to bathe a large basking platform in strong UV-B for several animals, there’s nothing like it.


IX.) UV-B Light Meters


            Many people don’t trust manufacturer or web site output claims; they want to measure their bulbs’ output themselves. Precisely measuring electromagnetic radiation nanometer-by-nanometer is done with a spectrophotometer, a very expensive piece of scientific equipment. Luckily there are affordable light meters for measuring overall output in a given range (for example, UV-B, UV-A, etc…). These meters won’t tell you a nanometer-by-nanometer breakdown, but can give an overall ‘ball park’ figure for how much output is in a range (i.e.: total UV-B output). Better yet, they’ll save money since rather than change UV-B bulbs every 6 months, you can monitor output & use them until it drops too low. 

            The Yahoo! Discussion Group for UV-B Light Meter Owners hosts a knowledgeable membership equipped with the Solarmeter 6.2. They occasionally do a group buy of the Solarmeter 6.2 & get a great price. I know of no equivalent competing product. For a good price right away, hit Reptile UV & get the Solarmeter 6.2 for $179 (as of 2-14-05). It’s believed the ZooMed UVB Digital Ultraviolet Radiometer ST-6 (~ $250) is the same product. 

            I recommend buying the Solarmeter 6.2 via the Yahoo! Group. It’s very easy to use. It looks like a little metal deck of cards. The sensor is a little round ‘button-like’ projection on top. On the front is a button. You point the sensor (top) at the source of UV-B you want to measure, at whatever distance you want to measure it at, press the front button & an LCD readout in µW/cm2 gives your answer. You can move it around back & forth with the button depressed & watch UV-B intensity vary from some sources (i.e.: some mercury vapor bulbs). Tip: leave a bulb on several minutes before you measure the UV-B output. 

            The skeptical may ask how good a ‘cheap’ UV-B light meter could be, or whether its readings are useful since they aren’t ‘absolute’ readings. You should join the Yahoo! Discussion Group for UV-B Light Meter Owners (free) to get access to their Files section, then read Robert MacCargar’s file on the Absolute Readings Issue. Some highlights from that file:

1.)    A broadband handheld meter is picking up (in this case) the average UVB total under the response bell curve from 280-320 nm. That's good enough for meaningful relative comparisons.” – in a reply from Solarmeter.

2.)    To get ‘absolute’ readings (i.e.: a nanometer by nanometer measurement of UV-B intensity across the entire UV-B range), you’d need an extremely expensive spectral radiometer.

In that file MacCargar goes on to state “The 6.2 Solarmeter is claimed to be within 5% accurate. Even with a 10% inaccuracy, it will give us good guidelines to look for,” & gives these examples:

Example #1: If we looking to give our reptile 50uW/cm2 at its basking area and the 6.2 is off by 10%, it could in actuality be 45uW/cm2 or 55 uW/cm2. These are all GREAT numbers and will suffice. 

Example #2: if you receive a reading of 10uW/cm2 it could really be 9uW/cm2 or 11uW/cm2. It would be wise to up the UVB readings accordingly. 

Example #3: Getting a reading of 6uW/cm2, who cares if it’s off by 10% and not an “absolute” reading? Get a new bulb!

3.)    Reptile UV’s website has this to say – "The Solartech’s Solarmeter 6.2 is the most accurate hand held ultraviolet radiometer UVB meter on the market. And although it’s a “broad band” meter, meaning its measuring the complete UVB range (280 nanometers to 320 nanometers) it peak sensitivity is at 295nm. This is the prime UVB needed to induce Vitamin D3 synthesis, making the 6.2 meter the perfect instrument to use to check your UVB reptile lamps.”


Note: on the Yahoo! Group Dave Weldon 1-24-05 after talking with Steve Mackin at Solartech reported the Solarmeter 6.2 is sensitive to humidity. Exposed to high humidity over many hours, the meter's zero point slowly develops an offset. Weldon took his meter out of his humid reptile room (the humidity was ~ 60-70%) and slowly over the day it returned to zero.  Mackin suggested storing the meter in a plastic bag with one of those little desiccant bags (some food or electronic packages have them) to prevent moisture getting past the meter's plastic casing. You can use it in a humid environment, but don't expose it to high humidity over many hours.  You may have too much humidity exposure if your meter doesn't read "000" anymore.”


X.) Comparing Popular UV-B Bulbs


            Disclaimers: Robert MacCargar is involved with Reptile UV & selling the Mega-Ray; he’s a competitor to other product lines. His reputation & credibility are very solid & I have no conflict-of-interest concern about consulting him in this article. Our statements RE: brand superiority are good faith statements based on our judgment of the information available to us. Be warned UV-B output & rate of decay of individual bulbs not only vary with brand, wattage & age, but also amongst individual bulbs of the same brand (say, 2 different T-Rex 160 watt Flood Active UV-Heat bulbs). Don’t compare one or two PowerSuns with 1 or 2 T-Rex Active UV-Heat bulbs & assume those findings apply to all their kind. Manufacturers may also change their products over time. When in doubt, consult resources such as the Yahoo! Discussion Group for UV-B Light Meter Owners for up-to-date discussions & resources on current products. Replacement recommendations are per MacCargar for people without UV-B meters; those with meters can delay replacement until production drops too far (i.e.: below ~ 15 µW/cm2).


            Appendix IV (Section XV) lays out reference data readings for the Sun & several commercial UV-B bulbs of varied brands, ages & distances from the meter. Our Comparisons draw on a range of online resources to give an overall view of performance, crediting (can’t have plagiarism; for the same reason (fair use), I only list a few of their readings, not all) & hyper-linking to the content owners (you may wish to explore their other offerings, well worth it).


ReptiSun 5.0 vs. ReptiGlo 8.0 vs. ReptiStar

            I asked Robert MacCargar, who has evaluated significant #’s of a range of UV-B bulbs over time, which tube fluorescent he considered best, the ZooMed ReptiSun 5.0 or the Hagen ReptiGlo 8.0. Considering UV-B output & also the spectrum (creative vs. destructive UV-B), in his opinion the ReptiSun 5.0 is best (as of 2-14-05) & also beats out the Sylvania ReptiStar popular in Europe. Replace every 6 months or monitor via meter.

Recommendation: ReptiSun 5.0 (but check out the 10.0 tube & compact versions. Time will tell whether they're reliable over time (i.e.: decay rate, etc...)).


ZooMed ReptiSun 10.0 Compact vs. ESU Reptile Super UV-Coil Lamp

            It’s our understanding the ReptiSun 10.0 compact fluorescent (26 watt) produces drastically more UV-B (maybe ~ 50 uW/cm2 @ 12” new) than the ESU Super UV-Coil Lamp (20 watt). It’s a little more expensive, but well worth it. There’s also a ZooMed ReptiSun 5.0 compact (not tube), but the 10.0’s output isn’t thought high enough to justify going with the weaker 5.0. It’s unclear when they should be replaced. With coil bulbs check whether your lamp has a reflector that's increasing your UV-B production; at close range it could become too intense.

Recommendation: ReptiSun 10.0 Compact.


Old-style T-Rex* Active UV-Heat vs. ZooMed PowerSun

            The T-Rex old-style Active UV-Heat & ZooMed PowerSun mercury vapor flood bulbs are roughly equivalent to each other but both are self-ballasted, may be subject to rapid UV-B drop-off & early failure, & are vulnerable to jostling when lit. Having used both 100 watt & 160 watt floods, I recommend the 160 watt floods for greater heat production (unless your tank is < 55 gallons; then use your judgment). Replace very 6 months or monitor via meter.

Recommendation: Use either one & stick to flood versions. 160 watt’s a good mid-range choice, but check out the Mega-Ray.

* Note: T-Rex bulbs are made by Westron, which in 2005 (after this article was originally written) allegedly switched over to manufacturing the new T-Rex Active UV-Heat 100 watt flood version with the design that was used to make Mega-Ray bulbs, resulting in a much higher UV-B output. If you purchase a T-Rex mercury vapor bulb UV-B flood bulb, you must determine whether it's 'old style' (which should be less common over time) or 'new style' (due to higher UV-B output). To 'follow the market' check out UV Guide's web site & the Yahoo! Discussion Group for UV-B Meter Owners.


Mega-Ray vs. PowerSun or old-style T-Rex Active UV-Heat

            The Mega-Ray 60 watt doesn’t produce much heat but the 100 watt does, so the 100 watt is more comparable to the other two. The Mega-Ray is available in self-ballasted (cheaper, higher fail rate) or externally-ballasted (more expensive but lower fail rate & worth the extra money); the 100 watt Mega-Ray & the other two are self-ballasted only at this time. The Mega-Ray’s warranty is not pro-rated; the other two have pro-rated warranties. The Mega-Ray is a ‘narrow flood’ with no spot option (& none needed!); the other two are offered in flood & spot versions, but I recommend sticking with floods unless you’re skilled & have a meter (maybe even then). The Mega-Ray is believed more likely to sustain higher UV-B output over an extended time than the other two, & the externally-ballasted version believed less likely to fail as early. The Mega-Ray should be replaced annually or monitor via meter. The Mega-Ray is offered by, a very reputable vendor & fine information site.

Recommendation: If you’ve got a meter & the determination to learn how to use your Mega-Ray to maintain solid UV-B production over time (adjust distance from basking platform, use a large enough basking platform to let the turtle choose its exposure), get a 60 watt externally ballasted (UV-B only) or 100 watt self-ballasted (UV-B and heat) Mega-Ray. If you’re going to set the bulb a fixed close distance (say, 8 – 12”) regardless, don’t have a meter & so won’t monitor the product (basically, ‘point & shoot’), stick to either of the others, probably a 160 watt flood. The newer version T-Rex 100 watt flood bulb (allegedly using Mega-Ray design) may be a viable alternative for some.


Some Notes on Comparing UV-B Options:

1.)    We don’t know just how much UV-B radiation turtles generally need, or how that varies by individual, gender, size, age, diet & species. Robert MacCargar considers ~ 50 µW/cm2 a decent figure to aim for; very likely enough, very unlikely too much.

2.)    Quality of UV-B (‘Creative’ UV-B, ~ 290-304 nm, vs. ‘Destructive’ UV-B) is very important (just like quantity in uW/cm2 is). A Solarmeter 6.2 can’t break it down for quality comparisons; we rely on the Yahoo! Discussion Group for UV-B Light Meter Owners & their resources to compare products’ UV-B quality (i.e.: ReptiSun 5.0 vs. ReptiGlo 8.0).

3.)    The ReptiSun 5.0 has a strong reputation for providing quality UV-B to reptiles; it tends to produce around 8-20 µW/cm2 within a foot distance, for the first 6 months of use (assuming ~ 12 hours/day use). We may speculate that such a product at that range is adequate (not necessarily ideal). The ReptiSun 10.0 is a newer product, hasn't stood as much 'test of time' yet, & has a more purplish light some people dislike aesthetically.

4.)    A reflector (of the correct type) can significantly increase (even double) UV-B output. For some tube fluorescents you should use one but be careful with close range or higher output bulbs (i.e.: ReptiSun 10.0).

5.)    ReptiSun/Iguana Light 5.0 (& possibly other good fluorescent UV-B bulbs) start out with modest UV-B production and degrade slowly over time. They should be within a foot of the basking animal. This level of UV-B isn’t likely to penetrate water or other obstructions (i.e.: tank-top metal screens) well.

6.)    Traditional Mercury Vapor Heat & UV-B Flood Bulbs (old-style T-Rex UV-Heat, ZooMed PowerSun) start out with strong UV-B still well short of direct noon sunshine, at 12” distances. Output drops off rather quickly, plateauing at lower levels which may last for months (but still degrade). Don’t put these bulbs too close when they’re new (unlikely, since close-up they’d overheat the basking platform). Be wary of the heat in smaller tanks (i.e.: under 55 gallon).

7.)    For those traditional mercury vapor bulbs, output is sufficiently variable over time that you may want a Solarmeter 6.2 & to research these bulbs with the resources this article hyperlinks; it’ll save you tossing some out at 6 months.

8.)    Mega-Ray bulbs put out so much UV-B that long exposure at close range could theoretically be dangerous to the animal. However, the turtle can limit exposure by leaving the basking spot or pulling into its shell. Be mindful of distance when using a Mega-Ray. For those applications they’re suited for (i.e.: suspended 2 feet over a large basking platform for a group of basking turtles), there is no current competition. The output decay rate is much less than with older mercury vapor bulbs; you can count on the Mega-Ray for a year. The newer version of the T-Rex Active UV-Heat 100 watt flood bulb will probably have similar conditions of use.

9.)    Outdoor UV-B levels vary widely with time of day, latitude, altitude, atmospheric conditions & direct sunlight vs. shade. That said, even in the shade on sunny days, or outdoors with full cloud cover, there’s often a lot more UV-B exposure than you’d get 12” from a brand new ReptiSun 5.0!


XI.) Summary & Recommendations.


1.)    Reptiles require Vitamin D3 to prevent metabolic bone disease (MBD).

2.)    There are 3 main routes to provide Vit. D3; dietary content (i.e.: commercial turtle diets or vitamin supplements), UV-B lighting or both. I do not recommend using concentrated liquid Vit. D3 products like T-Rex Solar Drops (here’s why). Large basking platforms offering the turtle choice of a range of UV-B levels are ideal. UV-B based Vit. D3 production is self-regulating but dietary Vit. D3 supplementation is not.

3.)    Dietary supplementation alone is probably sufficient from a strictly nutritional standpoint (i.e.: preventing MBD) & many turtles have prospered this way without UV-B lighting. That said, ‘dosing’ Vit. D3 is an inexact science.

4.)    UV-A may encourage comfort & natural behaviors but that’s speculative. It’s unlikely to cause harm, may be enjoyed & offer a more natural experience for the animal.

5.)    Only bulbs that advertise UV-B production produce significant amounts.

6.)    UV-B producing bulbs tend to run around $20-$75.

7.)    What your reptile most benefits from is a subset of UV-B light called D-UV-B. Mercury vapor bulbs are thought to produce more of their UV-B output in that range. You can’t specifically measure the amount of D-UV-B output with the meters we can afford. There’s also ‘destructive’ UV that can reduce Vit. D3 levels in the body.

8.)    UV-B bulbs are not commodity items; there’s a wide range of quality in output amount & degradation, & bulb reliability over time. While I’m unwilling to disparage specific products based on hearsay & knowing the manufacturer may improve, some products have erratic quality (may fail ridiculously early, provide little or way too much UV-B, etc…) & you’d better research any bulb you plan to use, especially if it’s some ‘Brand X’ bulb. We are advocating for good products, not pointing out the bad.

9.)    Unless you buy a UV-B light meter, you’re stuck relying on manufacturer claims & you’d better stick to a solid name brand, a known product (i.e.: ReptiSun 5.0, PowerSun (or T-Rex Active UV-Heat) 160 watt Flood, etc…) & with mercury vapor bulbs don’t place them too close to the basking area. Some reptiles (i.e.: some lizards) can get burned while basking (under any hot heat lamp, not just UV-B lamps) – I don’t know whether turtles can.

10.)            If you want a UV-B light meter, join Yahoo! Discussion Group for UV-B Light Meter Owners & join their next group purchase of the Solarmeter 6.2, or get it at Reptile UV ($179 as of 2-14-05).

11.)            Good brand-name fluorescents (i.e.: ReptiSun 5.0; the ReptiSun 10.0 tube & compact are too new for much consumer feedback at this time) should do fine for at least 6 months & some can be used up to 1 year. If you don’t have a UV-B meter, replace every 6 months.

12.)            Good brand-name mercury vapor bulbs (PowerSun, old-style T-Rex Active UV-Heat) are fine alternatives to fluorescents if you want to handle UV-B & heating chores in a single bulb. Be warned they have a high fail rate, tend to be short-lived (around 6 months, give or take) & over time their UV-B output may not live up to the hype (although they often produce more D-UV-B). Stick to flood versions & don’t get the bulb too close & you shouldn’t have to worry about giving your turtles too much UV-B. If you don’t have a UV-B meter, replace annually.

13.)            Both Mega-Ray bulbs, the new version of the 100 watt T-Rex Active UV-Heat Food bulb and the spot versions of PowerSun & T-Rex Active UV-Heat produce enough UV-B to be potentially dangerous to the animal if you don’t know what you’re doing. The Mega-Ray produces a wider area of strong UV-B & an externally-ballasted version (which I strongly recommend over self-ballasted to improve longevity) is available, & the output decay rate is much less. If you need this type of product, I recommend the externally-ballasted 60 watt Mega-Ray (or 100 watt self-ballasted, if you need a heat & UV-B combo. bulb) over its competitors. The 60 watt version is not a heat bulb, but the 100 watt version is. If you’re going to work with bulbs this powerful, get a UV-B meter.

14.)            UV-B lighting is an evolving industry; this article should be published Feb. ‘05. Be alert for changes in product lines.


XII.) Appendix I – Online UV-B Resources.


1.)    Turtle Forum’s Advanced Herpers’ Thread on UV-B Light Meter Use.

2.)    Turtle Forum’s Advanced Herpers’ Thread on Solar Drops – a discussion on the controversy involved & a basis for my recommendation you don’t use them.

3.)    Yahoo! Discussion Group for UV-B Light Meter Owners – Outstanding resource & I strongly recommend you join (free), peruse their files section & accept the frequently e-mailed posting digests (at least for awhile, while you’re learning). You can join even if you don’t have a meter, & this is (my opinion) the best place to get one (via group purchase).

4.) UV Guide - an online educational resource constructed by some of the same gurus from the Yahoo! UV-B Light Meter Owners' Group. This site is well-written, comprehensive yet comprehensible, & will likely remain more up-to-date than this article. Highly recommended.

5.)    Robert MacCargar of the Yahoo! Discussion Group for UV-B Light Meter Owners made a posting to the group 1-28-04 Re: Mercury Vapor bulbs7 that’s highly recommended reading. While it pre-dates the Mega-Ray, & other product lines may change over time, it’s a fine discussion about why self-ballasted mercury vapor bulbs have a higher fail rate, UV-B output decay in T-Rex Active UV-Heat & ZooMed PowerSun bulbs & other topics.

6.)    Russian Tortoise (by Joe Heinen) has this great Table on UV-B Output of Various Bulbs.

7.)    Beautiful Dragons, a website by Veronica Gomez dedicated to Bearded Dragons & their health, provides the highly informative Project UV-B Page. You can see a lot of readings on varied UV-B bulb brands at various distances & bulb ages. You can also get a feel for the variation across bulbs within a line (i.e.: test results for different 160 watt Flood PowerSuns at different ages & distances).

8.)    Reptile UV – Marketing the Mega-Ray, & offering a wealth of free online information re: it & related topics. Highly recommended.

9.)    Calcium Metabolism and Metabolic Bone Disease – by Melissa Kaplan, Melissa Kaplan's Herp Care Collection, Last updated August 17, 2002, ©1995, 2002 Melissa Kaplan.

10.)    Rickets Page at Medline Plus.

11.)            Veterinary Care for Your Chameleon – by Kenneth Lopez, D.V.M., article on The Chameleon Journals web site – excellent compact but dense discussion of calcium metabolism & the role of Vitamin D3.

12.)            Lighting for Chameleons – Part #1 – by Andy Beveridge. A well-written discussion of UV-B with info. useful generally.

13.)            UV-lamps for Terrariums: Their Spectral Characteristics and Efficiency in Promoting Vitamin D3 Synthesis by UVB Irradiation - by Jukka Lindgren. Originally published by the Herpetological Society of Finland [Herpetomania 13(3-4), 2004]. Highly recommended for discussion of creative vs. destructive UV-B & relative ‘value’ UV-B production of some commercial bulbs, but be sure to read the follow-up discussion between Lindgren & Robert MacCargar (important re: rationale for changing bulbs every 6 months in absence of a UV-B meter).


XIII.) Appendix II – Where to Get a UV-B Meter.


1.)    Join Yahoo! Discussion Group for UV-B Light Meter Owners & join their next group purchase of the Solarmeter 6.2.

2.)    Go to ZooMed’s Web Site & take a look at the ZooMed UVB Digital Ultraviolet Radiometer ST-6, priced at $250 direct from ZooMed as of 1-16-05. Warning before you buy: a # of people think this is a repackaged Solarmeter 6.2 that you could buy much cheaper via the group purchase I told you about in 1.).


XIV.) Appendix III – What is Electromagnetic Radiation?


            Electromagnetic radiation is made of little energy packets called photons. A photon moves in a straight line direction but zigs back & forth (moves in a wave pattern) along that line (axis); on paper this looks like a sine curve from Mathematics (your high school Math teacher was right; Math does follow you around…). Here’s a crude representation: 


            Now, imagine a photon is following that curving line, moving from left-to-right. The horizontal line shows the direction it’s going. Each one of those big ‘hills’ is called a wave. The highest point of a wave is its crest. The distance from one top wave crest to the next is called wavelength (measured in nanometers, nm). If you shorten or lengthen the wavelength you change the type of energy (like from heat to light to ultraviolet light). Higher energy electromagnetic radiation has a shorter wavelength. 

            Electromagnetic radiation comes in many forms; radio waves, microwaves, infrared (‘heat’), visible light (red, orange, yellow, green, blue, indigo & violet are the primary types; combine them all & you get white light), ultraviolet light, X-Rays & Gamma rays. The amount of energy in the photons determines the type of radiation. These forms differ by wavelength & frequency; you start with heat (long wavelength, low frequency, low energy), then you cram more & more waves onto that line, changing the radiation from heat to radio waves to microwaves to infrared to visible light & so on…


XV.) Appendix IV - UV-B Meter Readings for Popular UV-B Products.


1.)    ZooMed ReptiSun 5.0 (same as their Iguana Light 5.0).

Beautiful Dragons Project UV-B4: A few of her reported findings.

18” ReptiSun 5.0 (tested by Veronica Gomez)

New: 24 µwatts/cm2 @ 6”, 10 µW/cm2 @ 12”.

                  ~ 4-5 months old: 20 µW/cm2 @ 6”, 8 µW/cm2 @ 12”.


Yahoo! Discussion Group for UV-B Light Meter Owners – Database of UV-B Readings (one database for tube lights, one for mercury vapor bulbs) – by Theldara.

By Yahoo! Group member Lilacdragon.

Dataset I – 24” Iguana Light 5.0 with reflector, 11 days old.

      93 µW/cm2 @ 6”, 40 µW/cm2 @ 12”.

Dataset II – 24” Iguana Light 5.0 without reflector, 30 minutes old.

      56 µW/cm2 @ 6”, 24 µW/cm2 @ 12”.

Dataset III – 24” Iguana Light 5.0 with reflector, 30 minutes old.

      100 µW/cm2 @ 6”, 48 µW/cm2 @ 12”.

                  Note: the reflector makes a difference! 


      Table on UV-B Output of Various Bulbs (Russian (by Joe Heinen))

                  ReptiSun 5.0 (? Age & length?)

                              10 µW/cm2 @ 12”.


~ 4 month old ReptiSun 5.0 (on ~ 24/7 – constantly!) Up to 20 µW/cm2 @ ~ 6”  & up to 9 µW/cm2 @ ~ 12” (by Richard Lunsford via Solarmeter 6.2).


2.)    Exoterra ReptiGlo 8.0.


Yahoo! Discussion Group for UV-B Light Meter Owners – Database of UV-B Readings (one database for tube lights, one for mercury vapor bulbs) – by Theldara.

By Yahoo! Group member Lilacdragon: 24” ReptiGlo 8.0 with reflector, 25 days old.

      58 µW/cm2 @ 6”, 26 µW/cm2 @ 12”.

By Yahoo! Group member Brian: 24” 20 watt ReptiGlo, 3 months old.

       34 µW/cm2 @ 10”.


3.)    ESU Super UV Coil Lamp 20 watt version.

      Table on UV-B Output of Various Bulbs (Russian (by Joe Heinen))

                  20 watt Version (? Age)

                              3 µW/cm2 but distance not given, so reading not very useful.


4.)    Old-style T-Rex 100 watt Flood Active UV-Heat. (Note: Mercury Vapor bulbs have much more uneven UV-B radiation than fluorescents).

Beautiful Dragons Project UV-B4: A few of her reported findings.

T-Rex Active UV-Heat (tested by Veronica Gomez)

New: 41 µW/cm2 @ 6”, 16 µW/cm2 @ 12” (elsewhere she listed 44/93, & 16/99, leading me to believe there was a wide range of readings. The single readings taken were directly below the center of the bulb).

                              ~ 4 months old: 12 µW /cm2 @ 6”, 4 µW/cm2 @ 12”.

            Keep in mind T-Rex allegedly switched to the Mega-Ray design for their 100 watt flood Active UV-Heat bulb. Results shown above are for the older version of the bulb.

      Table on UV-B Output of Various Bulbs (Russian (by Joe Heinen))

      Lists 1 or 2 100 watt floods, but on a table where bulbs may be either T-Rex Active-UV-Heat or ZooMed PowerSun! (I take it he views them as similar). Ages not given. One bulb produced 50 µW/cm2 at 12”, & another (or the same) bulb 12.5 µW/cm2 at 24”.


5.)    T-Rex 160 watt Active UV-Heat.


      Table on UV-B Output of Various Bulbs (Russian (by Joe Heinen))

      4 Listings, but on a table where bulbs may be either old-style T-Rex Active-UV-Heat or ZooMed PowerSun! (I take it he views them as similar). Ages not given. Listings include 85 µW/cm2 @ 12”, 65 µW/cm2 @ 18”, 25 µW/cm2 @ 24” & 11 µW/cm2 @ 36”.


6.)    ZooMed PowerSun 160 watt Flood Bulb.

Beautiful Dragons Project UV-B4: A few of her reported findings.

ZooMed 160 watt Flood PowerSun (tested by Veronica Gomez)

                              New: 115 µW/cm2 @ 6”, 47 µW/cm2 @ 12”.

                              ~ 4 months old: 22 µW/cm2 @ 6”, 8 µW/cm2 @ 12”.

At the same web page are cited many measurements taken by Cheri S. of Reptile Rooms and Reptile Rap. Interestingly, she tested this same type of bulb & at age 1 year, a PowerSun gave readings of 31 µW/cm2 @ 6”, 12 µW/cm2 @ 12” for one bulb, & 99 µW/cm2 @ 6”, 31 µW/cm2 @ 12” for another (same age). Both 160 watt flood PowerSuns.


      Table on UV-B Output of Various Bulbs (Russian (by Joe Heinen))

      4 Listings, but on a table where bulbs may be either old-style T-Rex Active-UV-Heat or ZooMed PowerSun! (I take it he views them as similar). Ages not given. Listings include 85 µW/cm2 @ 12”, 65 µW/cm2 @ 18”, 25 µW/cm2 @ 24” & 11 µW/cm2 @ 36”.


    4 month old 160 watt flood PowerSun (on ~ 14 hours/day) ~ 64 µW/cm2 @ ~ 6” & ~ 23 µW/cm2 @ ~ 12” (by Richard Lunsford via Solarmeter 6.2).


7.)    Westron Mega-Ray mercury vapor 60 watt Flood Bulb.


      Table on UV-B Output of Various Bulbs (Russian (by Joe Heinen))

                  (? Age)

                               250-300 µW/cm2 @ 12”.

125+ µW/cm2 @ 48”. 


Yahoo! Discussion Group for UV-B Light Meter Owners – Database of UV-B Readings (one database for tube lights, one for mercury vapor bulbs) – by Theldara.

By Yahoo! Group member Lilacdragon: Mega-Ray Externally Ballasted 60 watt ‘PAR 38 flood’ bulb after 300 hours burn time (~ 25 days old).

      497 µW/cm2 @ 12”, 209 µW/cm2 @ 18”, 135µW/cm2 @ 20”.


8.)    Westron Mega-Ray Self-Ballasted 100 watt Bulb.


      Table on UV-B Output of Various Bulbs (Russian (by Joe Heinen))

                  (? Age)

                               150-250 µW/cm2 @ 12”.

100-150 µW/cm2 @ 20”.


9.)    Mega-Ray Self-Ballasted 160 watt Bulb.


      Table on UV-B Output of Various Bulbs (Russian (by Joe Heinen))

                  (? Age)

                               250-300 µW/cm2 @ 18”.

75-150 µW/cm2 @ 24”.


10.)            The Sun.


On Wild Inside’s web site there’s a Table listing data measurements of UV-B taken by David Krughoff  with a hand held photodiode radiometer on a clear day, 6/29/00, at Hoyleton Illinois USA.3 Here are a few measurements (in µW/cm2) from that set:


Time of Day                In Direct Sun.             4 Feet into Shade (from Direct Sun).


      8 a.m.                                      74                                            ---

      9 a.m.                                      142                                          ---

      Noon.                                      256                                          ---

      1 p.m.                                      269                                          54

      3 p.m.                                      239                                          ---

      4 p.m.                                      187                                          30

      5 p.m.                                      131                                          22


      Take Home Lessons about the Sun:

1.)    UV-B intensity is very uneven over the course of the day, heavily concentrated late-morning & early afternoon.

2.)    UV-B intensity in shaded areas is often much greater than the direct UV-B output of popular fluorescent UV-B bulbs, & comparable to direct exposure from some mercury vapor UV-B bulbs at a distance of 1 foot.


Table on UV-B Output of Various Bulbs (Russian (by Joe Heinen)

                  South Carolina @ Noon 11/22/04 in full sun: 220 µW/cm2.


      Hopkinsville, Southwestern KY, 1-16-05 @ 1:30 p.m. during snow with full cloud cover (by Richard Lunsford via Solarmeter 6.2): readings up to 40 µW/cm2.


      Hopkinsville, Southwestern KY, 1-17-05 @ Noon on totally clear, blue sunny day (by Richard Lunsford via Solarmeter 6.2): readings up to 140 µW/cm2. On the opposite side of the house from the sun, standing several feet into the shade, readings varied from the 20’s up to around 40 µW/cm2


XVI.) Appendix V - Brief Testimonials & Reports.


1.)    TF Global Moderator Acutus (Billy) – “I insist on having it with my hatchlings where I can almost assure you it works! If any of you remember last year I had a hatchling with a shell problem. The only thing i did was to add a ReptiGlo 8.0 bulb and within a month or so I could see the problem correcting itself. I do tend to think though that the same thing could be accomplished through supplementation.
I had a RES when I was about 5 and he lived for 20 years. he never had anything more than a house light bulb above his basking ramp and was perfectly fine. We did take him out frequently on warm days however.”

2.)    Why the Active UV Heat Lamp is an Important Advance -  Don Gillespie, DVM El Paso Zoo, cited on Wild Inside’s Website – Discussed normalization of Vit. D3 levels & discernable benefit in a female crocodile monitor via use of a 300 watt Active UV Heat spot bulb (not T-Rex’s) for 4 months at 2 – 2.2 meter distance for 8-10 hours/day. Mention of other animals, including possible appetite benefit in reluctant feeders.

3.)    A Report RE: 2 Komodo Dragons (including sunlight vs. UV-B spot bulb comparison), a water monitor & a Burmese Python treated with Active UV Heat (not T-Rex’s) with Vit. D3 normalization & observable benefit - Sincerely, Beth Jo Schoeberl, Tropics Zoologist, Minnesota Zoological Garden.

4.)    Reptile UV’s Website sells Mega-Ray bulbs & on the product pages are many glowing testimonials.

5.)    Kory Steele, Vice-President of the Virginia Herpetological Society & Curator of Amphibians & Reptiles at Virginia Living Museum as of 2-3-05 spoke highly of the Mega-Ray from personal experience.


XVII.) Appendix VI.) Mercury in UV-B Bulbs.

            TF member Bob McNally (Bobmc) noted that all fluorescent lights (tube or screw-in style) contain mercury. So do mercury vapor bulbs! Robert MacCargar noted in fluorescents mercury clings to the phosphor powder in the tube and this powder floats in the air and gets everywhere if the tube is broken. The mercury in the MV lamp is in a very hard quartz tube that should require great force to expose and there is much less mercury in the MV lamp than tube fluorescents. This, combined with the fact that there isn’t any ‘dust’ to cling to in mercury vapor bulbs should make them safer. 

            Mercury is hazardous to humans & formal risk assessment & recommendations are beyond the scope of this article. MacCargar considers is judicious to air out a room after a fluorescent bulb break, remove the substrate & drain and refill any tanks. I recommend you dispose of your UV-B bulbs responsibly via recyclers. 

            The Assoc. of Lighting & Mercury Recyclers has an online presence. You can learn more about how & why mercury is used in lighting, & get some idea of the rough dangerousness of mercury-containing lighting here. 

Environment, Health and Safety Online maintains a list of Mercury Recyclers. The also have the EHSO’s Fluorescent Lights and Lighting Disposal & Recyling Page – go to the Mercury-Containing Lamps section

The South Dakota Dept. of Environment & Natural Resources offers a list of Fluorescent Bulb & Mercury Recyclers. 

Disclaimer: The author & consultants for this article cannot & do not claim or imply a professional knowledge of mercury or health-management issues related to mercury or any other aspect of lighting; any recommendations given are well-intentioned lay recommendations.


XVIII.) Bibliography.


1.)    Making Sense of Reptile Lighting, by Gary Bagnall. Janauary 2004 issue of Reptiles Magazine. 

2.)    Diffey, B. L. 1991. Solar ultraviolet radiation effects on biological systems. Review in Physics in Medicine and Biology 36 (3): 299-328. (Cited Online at Wild Inside’s Website, at this link). 

3.)    Measurements taken by David Krughoff  with a hand held photodiode radiometer on a clear day, 6/29/00, at Hoyleton Illinois USA.3 (Cited Online at Wild Inside’s Website, at this link). 

4.)    Beautiful Dragons, a website by Veronica Gomez dedicated to Bearded Dragons & their health, provides the highly informative Project UV-B Page. You can see a lot of readings on varied UV-B bulb brands at various distances & bulb ages. You can also get a feel for the variation across bulbs within a line (i.e.: test results for different 160 watt Flood PowerSuns at different ages & distances). 

5.)    Russian (by Joe Heinen) has this great Table on UV-B Output of Various Bulbs. This is a fine & reputable site dedicated to the Russian Tortoise. 

6.)    Yahoo! Discussion Group for UV-B Light Meter Owners – Database of UV-B Readings (one database for tube lights, one for mercury vapor bulbs) – by Theldara. 

7.)    Robert MacCargar of the Yahoo! Discussion Group for UV-B Light Meter Owners made a posting to the group 1-28-04 Re: Mercury Vapor bulbs that’s highly recommended. While it pre-dates the Mega-Ray, & other product lines may change over time, it’s a fine discussion about why self-ballasted mercury vapor bulbs have a higher fail rate, UV-B output decay in T-Rex Active UV-Heat & ZooMed PowerSun bulbs & other topics. 

8.)    Practical Encyclopedia of Keeping & Breeding Tortoises & Freshwater Turtles – A.C. Highfield, Carapace Press, c/o The Tortoise Trust, BM Tortoise, London, England. First Ed. 1996. 

9.)    Calcium Metabolism and Metabolic Bone Disease – by Melissa Kaplan, Melissa Kaplan's Herp Care Collection, Last updated August 17, 2002, ©1995, 2002 Melissa Kaplan. 

10.)            Osteomalacia page, under Osteoporosis and Bone Physiology – online site maintained by Susan Ott, M.D., Associate Professor, Dept. of Medicine, Univ. of Washington. 

11.)            High growth rate diets and vitamin D3 - a response - A. C. Highfield – online article at

12.)            Veterinary Care for Your Chameleon – by Kenneth Lopez, D.V.M., article on The Chameleon Journals web site. 

13.)            Bernard, J.S., O.T. Oftendal, P.S. Barboza, M.E. Allen, S.B. Citino, D.E. Ullry and R.J. Montali. (1991) The response of vitamin D deficient green iguanas (Iguana iguana) to artificial ultraviolet light. Proc Am Vet 1991:147-150. 

14.)            Chen, T.C. 1999. Photobiology of vitamin D. In M.F. Holick (ed.), Vitamin D: Molecular Biology, Physiology, and Clinical Applications, pp 17-37, Humana Press, Totowa, New Jersey. Cited by Herpetological Review 35(4), 2004, Pages 361-364. 

15.)            Holick, M.F. 2004. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. Amer. J. Clin. Nutrit. 79:362-371. Cited by Herpetological Review 35(4), 2004, Pages 361-364. 

16.)            Gehrmann, W.H., D. Jamieson, G.W. Ferguson, J.D. Horner, T.C. Chen and M.F. Holick. 2004. A Comparison of Vitamin D-Synthesizing Ability of Different Light Sources to Irradiances Measured with a Solarmeter Model 6.2 UVB Meter. Herpetological Review, 2004, 35(4), Page 361-364, © 2004 by Society for the Study of Amphibians and Reptiles. 

17.)            UV-lamps for Terrariums: Their Spectral Characteristics and Efficiency in Promoting Vitamin D3 Synthesis by UVB Irradiation - by Jukka Lindgren. Originally published by the Herpetological Society of Finland [Herpetomania 13(3-4), 2004]. Highly recommended for discussion of creative vs. destructive UV-B & relative ‘value’ UV-B production of some commercial bulbs, but be sure to read the follow-up discussion between Lindgren & Robert MacCargar (important re: rationale for changing bulbs every 6 months in absence of a UV-B meter).