What is UVB Light?
UV light or Ultraviolet light is high energy light than violet but lower energy than X-rays on the electromagnetic spectrum. Ten percent of the light energy produced by the sun is UV light. UV light is invisible to most humans. Small birds, on the other hand, have a forth color receptor in their retinas that gives them “true” UV vision.
UV light is further broken up into UV-A, UV-B, and UV-C.
UV-A is low wave UV. It easily penetrates the ozone layer. This is the light we find in black lights and is known as “soft” UV. Reptiles utilize this light to help regulate behaviors (a.k.a. their circadian rhythm) such as feeding, daytime movement, mating, and similar activities.
UV-B is medium-wave UV or “intermediate” UV and most of this light frequency is absorbed by our ozone layer. Biologically, it is utilized by non-fish vertebrates like reptiles, amphibians, birds, mammals, and even humans for vitamin D synthesis.
UV-C is short-wave UV or “hard” UV. It is ionizing radiation and used in germicidal UV sterilizers. Luckily, the UV-C produced by our sun is completely absorbed by the ozone layer and our atmosphere.
Why do reptiles need UVB light?
Reptiles, like many vertebrates, utilize UV-B light in the synthesis of vitamin D. When UV-B light interacts with the skin it interacts with 7-dihydrocholesterol activating it into cholecalciferol, or vitamin D3. From there it undergoes further transformation within the liver and kidneys to become 1,25-dihydroxyvitamin D3 used for maintenance of calcium balanced within the body. So without UV-B light that first step in producing this vital chemical regulator within the body never happens. 1,25-dihydroxyvitamin D3 is important as it increases absorption of calcium from the diet, decreases loss of calcium in the urine from the kidneys, prevents overproduction of parathyroid hormone, and modulates the activity if the cells of the skeletal system.
Do all reptiles need UVB light?
Diurnal reptiles, such as iguanas, bearded dragons, turtles, tortoises, water dragons, day geckos, etc. all require UV-B for production of active vitamin D3. Crepuscular reptiles, those active at dawn and dusk, have been found to also be able to utilize UV-B to activate vitamin D3. However, they can also utilize dietary vitamin D3 and have been raised in captivity for generations without UVB lighting. Studies in nocturnal reptiles (i.e. pythons, boas) have shown they cannot utilize UV-B for vitamin D3 activation. However, there may be additional benefits that UV-B lighting provides that have yet to be discovered.
What sources of UVB lighting are available to pet owners?
UV-B light for your reptile can be naturally provided from the sun or artificially by using specially designed light bulbs that produce UV-B. Natural sun can only be used by reptiles housed outside. This is because UV-B cannot penetrate glass so placing your pet near a window will not work. UV-B is only able to penetrate the glass of UV-B bulbs because the glass has been specially treated to allow UV-B to penetrate the glass. This coating wears off over 6-12 months of use causing these bulbs to stop producing UV-B light long before they burn out. This is why manufacturers recommend replacing these bulbs regularly. Artificial UV-B is available in 4 different types of reptile bulbs: fluorescent, mercury vapor, metal halide, and LED.
The first is fluorescent which produces light using a low-pressure mercury-vapor gas-exchange lamp that fluoresces to produce visible light. These bulbs produce minimal heat and come in 3 types. The first are the T8 bulbs, this is a second generation fluorescent straight tube bulb (first generation being T12 bulbs and are no longer produced as UV-B bulbs). The second are the compact fluorescent bulbs where the fluorescent tube is formed into a coil or loop and then set into a normal light bulb socket. Both T8 and compact fluorescent bulbs produce similar amounts UV-B. The third and newest type are the T5 or third generation straight tube fluorescent bulbs. These emit stronger light and have more UV-B production than both T8 and compact fluorescent bulbs.
Most UV-B fluorescent bulbs are sold in various strengths, which vary in their labeling depending on the manufacturer. For example, Zoo Med sells them as 2.0, 5.0, and 10.0 bulbs corresponding to 2%, 5% and 10% UV-B production respectively. While Arcadia sells 2%, 7%, 10%, 12% and 14% bulbs. Exo-Terra takes a completely different aproach utilizing a more complex system to help keepers choose the correct bulb based on species and basking distance with bulbs labeled as 100, 150, or 200.
The second type of UV-B bulb available to reptile owners are Mercury Vapor bulbs. A mercury-vapor lamp is a gas-discharge lamp that uses an electric arc through vaporized mercury to produce light. They procude both head and UV-B light. These bulbs are ballasted, when they turn off they need to cool down before they will turn back on, so they cannot be regulated with a thermostat like standard heat lamps. They have a higher UV penetration and UV index than fluorescent bulbs making them ideal for larger enclosures (40 gallons or larger).
Metal Halide bulbs are the third type available on the market. A metal-halide lamp is an electrical lamp that produces light by an electric arc through a gaseous mixture of vaporized mercury and metal halides. This bubl also produces both heat and light, but less heat at a lower wattage than mercury vapor bulbs. These high intensity UV-B bulbs also work well for larger habitats. It should be noted that special fixures are required for these and standard heat domes will not work.
The final type available are LED or light-emitting diode lamps. These are a semiconductor light source that emits light when current flows through it. Relatively new to the market, more research is needed to really gauge how they compare to other bulbs on the market. While expensive, these bulbs are energy efficient and produce little to no heat.
What is UV penetration and why is understanding this important to choosing the right lighting for your pet?
UV penetration is the concept that the farther you get from the UV-B source, the lower the UV-B index is. Different bulbs are going to give you different depths of penetration into the cage. It is important to take this into account when choosing the lighting for your pet. In general, mercury vapor and metal halide bulbs have the highest (or deepest) penetration while fluorescents the penetration is lower. Below are some examples of UV penetration diagrams for a variety of different UV-B bulbs.
What is UV index?
The last area that needs to be touched on is UV index. UV index is an international standard measurement of the strength of sunburn-producing ultraviolet radiation at a particular place and time. It’s an open-ended linear scale, directly proportional to the intensity of UV radiation that causes sunburn on human skin. It was invented to help people effectively protect themselves from UV radiation, which has health benefits in moderation but in excess causes negative effects. We borrow this in reptiles just as a measure of the amount of UVB reaching our pets.
Summary
UV-B lighting is essential for the health of many pet reptiles. Most reptiles require UVB lighting to properly absorb and utilize dietary calcium. Without UVB many reptiles will develop Nutritional Secondary Hyperparathyroidism a.k.a. “Metabolic Bone Disease.” It is important to understand that artificial UVB lights need to be changed every 6-12 months as they will stop giving off UVB light. Both species and cage setup should be considered when choosing the right UVB source.
For more information on UV-B light – click here.
For more inforamtion on Nutritional Secondary Hyperparathyroidism – click here.