| What Exactly Does Ultra-Violet Light Do?
The longest ultra-violet (ultra means beyond) radiation waves, being just shorter than violet colored light, which is the shortest electro-magnetic energy visible to the human eye, are invisible to us. Ultra-violet light is divided into three categories depending upon its wavelength, UVC, UVB and UVA. All can have a greater or lesser actinic effect. Actinic means that they can have a marked effect on chemical and biological processes. The shortest ultra-violet radiation waves (those less than 280 nm) from the sun are referred to as UVC, and are absorbed by the ozone in our atmosphere, and do not normally penetrate to the surface of the earth. This is just as well, though the so-called greenhouse effect, which causes holes in the ozone layer, is worrying, because it is these shortest ultra-violet radiation waves that are the most actinic and therefore the most harmful. They cause damage to the retina in eyes, kill bacteria and can even cause genetic damage. Artificial lights producing mainly UVC light are used for sterilizing water in ponds and aquariums in sealed containers that let none of this dangerous light escape. All ultra-violet light is relatively easily deflected or absorbed, particularly by normal glass. None of the specialist UVB lamps on the market emit this harmful UVC light.
The range of UVB light is generally accepted as that emitted in wavelengths between 280 nm (nanometers) to 320 nm, whilst UVA is that between 320 nm to 400 nm. In terms of vitamin D3 photo-biosynthesis UVB wavelengths in the range 290 nm to 300 nm wavelength range are the generally thought to be the most effective, being responsible for as much as 60% of all photo-biosynthesized vitamin D3. It is generally believed that only about 5% of D3 is photo-biosynthesized by wavelengths greater than 310 nm. What UVB of the correct wavelength actually does is penetrate the skin, having an actinic effect on sterols, such as cholesterol, circulating in the blood capillaries just beneath the skin. This product is chemically changed by this photo-biosynthesis into pre-vitamin D3, which then becomes vitamin D3 by a temperature dependant chemical reaction (thermal isomerization). This product is transported by blood plasma proteins to the liver and kidneys for both long-term storage and further conversion to several other active forms of the vitamin. It is this multiplicity of active forms that has led many scientists to think of vitamin D3 more as a hormone rather than just a vitamin. This storage of vitamin D3 in the liver is why reptiles that feed on whole vertebrate prey, such as whole rodents, do not require extra in their diet, or exposure to UVB light. Their total vitamin D3 requirement comes from the liver of their prey. It is only insectivorous, herbivorous and omnivorous reptile species that are likely to require either dietary vitamin D3 or exposure to UVB light in captivity.
UVA light is produced in much larger quantities, even by those lamps designed to have significant UVB output, including T-Rex Active UVHeat lamps. UVA is important for the normal behavior of many reptiles, particularly diurnal lizards, as this is light that many of them can see, even though we cannot. It can be important for their reproductive and other behavioral needs. For example many lizards can determine the sex of each other using UVA light. Appetite can also be stimulated in many reptiles following exposure to significant amounts of UVA light. Many insects have ultra-violet reflectance patterns on them that reptiles can see and so this helps them to detect and capture their prey.
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