UVB has a wavelength of 280-320 nm. Many reptiles, especially diurnal species originating from the tropics, rely on UVB to synthesize the precursor to Vitamin D3 in their skin.
UVA light has a longer wavelength of 320-400 nm. Although not essential, it may improve your reptile's quality of life and breeding potential.
Which Animals Need UVB?
Heliothermic reptiles (those that bask in the sun) generally require UVB. Many of these species have adapted to spending large amounts of time basking by either exposing themselves to the sun in the morning and early evening and/or limiting the amount of radiation they actually absorb through unique characteristics of their skin. Examples of heliothermic reptiles include most turtles, all tortoises, diurnal lizards, and crocodilians.
All amphibians, snakes, snapping turtles, and nocturnal lizards are able to obtain Vitamin D3 in sufficient quantities through their diet and do not require specific UVB lighting.
Providing UVB to Reptiles
Natural sunlight is the best source of UVB, but this can only be used in outdoor screen or wire enclosures. Animals kept in this manner must have access to shade at all times as well to avoid overheating or overexposure.
Fluorescent UVB Bulbs
Studies by hobbyists and scientists alike have shown that Zoo Med's Reptisun 10.0 series of fluorescent bulbs are superior to most other models and accurately reflect their intended use. The highest UVB levels are found within 6 inches of the bulb, and output declines by 80-90% at 18 inches from the bulb. Because of this, basking sites should be located relatively close to the light source- ideally, for any reptile that actively climbs there should be a series of perches or basking areas at various distances from the heat and UV source.
The light spectrum of fluorescent bulbs changes over time, and the amount of UVB will gradually decrease even as the bulb continues to emit visible light. It is important to make note of the bulb's useful life as stated by the manufacturer and replace your UVB lights regularly.
Fluorescent reptile bulbs provide little heat- it is advisable to situate UVB sources next to a heat source such as an incandescent bulb to mimic the sun and allow your reptiles access to UV each time it seeks warmth.
Halogen and Mercury Vapor UVB Bulbs
These bulbs generally emit higher levels of UVB at greater distances than fluorescent tubes or spiral compact bulbs. They are useful for tall cages as well as for desert-dwelling reptiles with high UVB requirements. Unlike fluorescent bulbs, mercury vapor bulbs also give off heat and may eliminate the need for an additional heat source.
Full Spectrum Bulbs
The designation "full spectrum" generally refers to the spectrum of visible light, so while these bulbs are excellent for applications where natural-looking light is desired they provide no UVB for reptiles. This is true for household fluorescent bulbs as well, as they are not designed to emit UV.
Which UVB Bulb is best for my Pet?
The ideal bulb will depend upon your reptile's natural history as well as the type of enclosure used. Unfortunately, the UVB requirements of reptiles vary widely and little research has been done on the needs of specific reptiles in the wild, let alone the corresponding equipment in captivity. It is an inexact science to attempt to replicate the effects of the sun on reptiles kept in captivity, as many species may bask for short periods of time under intense light in the wild but spend more time basking under lower UVB levels in captivity as they have access to it for long periods of time on a regular basis. Because it is impossible to account for all of these variables we must rely on a few generalizations.
Desert reptiles, tropical reptiles that bask frequently, and juveniles have the highest needs. Included among these are Uromastyx lizards, chuckwallas, desert iguanas, tortoises, and semi-aquatic turtles. Reptiles that spend much of their active time beneath leaf litter or in densely forested areas with little light penetration may require less.
The ideal photoperiod for your reptile should ideally follow the seasonal cycle of its natural range. Tropical species can be kept with 12 hours of light per day, while temperate species may do better with a photoperiod that matches the seasons. However, many temperate reptiles thrive with a steady 12 hour day cycle. Because of the length of time these animals are able to access UVB each day, it is important to provide shelters that allow them to avoid the light and regulate their exposure.
A Note on UVA Radiation
UVA light has a longer wavelength of 320-400 nm. Although not essential, it may improve your reptile's quality of life and breeding potential. UVA is sensed by reptiles in the pineal gland, located near the brain. It functions in the regulation of circadian rhythms and is believed responsible for daily and seasonal changes in behavior and activity. In addition to encouraging natural behavior, it enables some reptiles to identify food and mates, and may be critical to the breeding success of certain species.
UVA can be provided by reptile bulbs that specifically make mention of emitting UVA on their packaging. This is present in fluorescent lights as well as some incandescent and halogen bulbs.
Types of Light
The various types of light are characterized by differing wavelengths, which are expressed in nanometers (nm). Wavelength is directly related to energy, with high wavelengths containing less energy and lower wavelengths being much more energetic. Light falls between microwaves and X-rays on the electromagnetic spectrum, and is further broken down into infrared, visible light, and ultraviolet.
There are three types of ultraviolet radiation, two of which are important to reptiles. These are UVA, which has the largest wavelenth, and UVB. UVC has the shortest wavelength and is energetic enough to be dangerous even in small exposure. However, virtually all UVC from the sun is blocked by the atmosphere. Humans cannot see UV light, but many reptiles and other animals are able to see UVA radiation and, like humans, benefit from certain amounts of UVB.
What is UVB Radiation?
UVB has a wavelength of 280-320 nm. Many reptiles, especially diurnal species originating from the tropics, rely on UVB to synthesize the precursor to Vitamin D3 in their skin. In general, these reptiles are unable to gain enough benefit from Vitamin D3 ingested as part of the diet, and for this reason they must bask in the sun, or in captivity, under UVB-emitting light sources.
Reptiles rely on Vitamin D3 in order to absorb the calcium in their diet and use it for various physiological functions. A Vitamin D3 deficiency will eventually result in developmental problems, deformities, and difficulties in normal body function which can lead to severe illness and even death.