It is true that metal halides produce UVB, but it is significantly less than a reptile MVB, it's even less than a UVB fluorescent tube.
Tests have been done on these products, these are facts.
uvheat.com/measure.html
"Bulb Type / Distance (ft)/ UVA / UVB
Reptisin 5.0 / 1 / 23 / 10
Vitalite / 1 / 6 / 1.6
Blacklight / 1 / 153 / 2.6
Metal Halide (100w)/ 1 / 40 / 1.9
Lumichrome / 1 / 4 / 0.9
Cool White / 1 / 2 / 0.1"
www.anapsid.org/liteheat.html
"Problems with Metal Halide Products
Metal halide products also produce visible light and ultraviolet A and B. However, they produce an excessive amount of UVA, which can cause skin and other cancers. Metal halides produce less UVB - less than Zoo Med's reptile and iguana UVB-producing fluorescents. Because of the danger to humans, many of these products contain shields which filter out the UVA and UVB...so much so that they can end up producing too little UVB for use with reptiles.
UVB (Ultraviolet B) and UVA (Ultraviolet A)
The only lights that can safely provide these two critical wavelengths to your diurnal reptiles are the UVB/A producing fluorescents made for the reptile pet trade. "
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It should also be noted that what plants use for photosynthesis is *not* UVB, it's the intensity and color of the light spectrum. Think about it, if UVB was that important for plants, why are greenhouses so successful? After all, glass filters out the UVB. Greenhouses work because the glass does not alter the visible spectrum of light.
The reason metal halide lights are recommended for plants is because they produce an abundance of light in the visible color spectrums that promote plant growth, very similar to the natural colors of sunlight. In fact most metal halides use shields specifically to reduce the UVA and UVB output. Even plant people will tell you that to get more UVB for certain plants you should upgrade to a reptile light because the UVB output is much greater.
You'll notice in the following sources explaining the benefits of metal halide lighting for plants, UVB is not once mentioned as a factor.
www.futuregarden.com/lighting/choosing_grow_lights.html
"A primer on photosynthesis
Plants have the unique ability to manufacture their own food. In the process known as photosynthesis, chlorophyll uses light energy to convert carbon dioxide from the air and water from the ground into food sugar. When these elements abound in a perfect environment, the production of food is limited only by factors that effect photosynthesis, being the intensity, color and duration of the daily light the plant receives."
homeharvest.com/whichgrowlightisrightforme.htm
"Metal halide is a highly efficient light source capable of delivering a white light in the range of 2700 to 5500 Kelvin degrees with typical Color Rendering Index (CRI) ratings in the mid-60's to mid-70's. Some lamp chemistries even obtain CRI's in the 80s. The CRI is an index that measures how closely an artificial light source matches the natural colors of sunlight, with 100 being a perfect score. In contrast, high pressure sodium lamps yield yellow lighting (2200K) and have a very poor color rendering index of 22.
By varying the blend of chemicals in the arc tube, metal halide engineers are able to alter the characteristics of the light output. This flexibility in design makes metal halide so versatile.
White light is a very important attribute of metal halide technology, because it is the closest to the natural sunlight that people prefer. Metal halide lamps are widely used where color rendering is important such as stadiums, manufacturing plants, malls, and supermarkets.
For horticultural purposes, metal halides tend to produce a shorter, more compact plant habit that more closely resembles plants grown outdoors. A plants appearance growing under most metal halide lamps is almost identical to those growing outside, which makes it the preferred lamp for use in living areas. Horticultural metal halide lamps have increased red spectrum added for increased fruiting and flowering without sacrificing plant appearance.
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www.living-learning.com/faq/faqhid.htm
"Metal Halide -These bulbs are high in blue green spectrum (which is needed to promote vegetative growth), with some red/ orange spectrum (needed to promote flowering). These lights lamps are used primarily ro promote stocky, lush vegetative growth."
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I guess you're lucky that your beardies are doing great, I mean they are maybe getting a little UVB from the light, and if you're supplimenting their diets that would have something to do with it too, but I certainly wouldn't recommend anyone go the cheap route on this one. For only $10-20 more you can get a bulb that outputs a much more suitable amount of UVB for your reptiles.
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Amanda
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2.0 bearded dragons (Ocho / Domo-kun)
1.0 pictus gecko (Nicodemus)
0.1 kingsnake (Rio)
0.0.1 tarantula (Calcifer)
1.0 ferret (Playstation)
1.0 cat (Wally)
0.1 dog (Tima)
