bulbs in the market that provide adequate UVB while also being safe when used appropriately. UVB bulbs can be further divided into linear fluorescent, compact fluorescents, and mercury vapor. In the future, commercial LED UVB lights may also become available. Fluorescent UVB bulbs provide light in the required wavelength for D3 synthesis but no heat. Mercury vapor bulbs provide both heat and UVB.
There are six main aspects to consider when selecting a UVB bulb:
1 Size/type of the enclosure.
2 Type of material between the bulb and the reptile.
3 Type of bulb.
4 Effective distance of the bulb.
5 Bulb longevity.
6 Species of reptile.
Another consideration is the type of fixture used for the bulb. There are a number of reptile‐specific fixtures that offer the advantage of having reflective materials to increase light reflection and decrease scattered light emission (radiation). Some also have a ceramic base and are more tolerant of higher temperatures produced by mercury vapor bulbs. Reptile‐specific light fixtures or those that reflect light away from the bulb and towards the animal are preferred over plastic fixtures or those without reflective properties.
T8 Linear Fluorescent Tubes
T8 bulbs (25‐mm or 1‐inch diameter) are available in different lengths and fit into standard aquarium or reptile hoods. Some manufacturers further classify their bulbs by a number system ranging from 2.0 to 10.0. This number represents the percentage of light that is emitted in the UVB spectrum. A 5.0 has 5% of the emitted light in the UVB spectrum; a 10.0 has 10% UVB emission, and so on. Arcadia® has simplified the process by simply stating the percentage of UVB emission with their bulbs ranging from 6% to 14%.
Being a longer bulb also means there is more scattered radiation so the UVB exposure is not as focused. One recommendation is that the longest bulb possible be used to cover a wide area of the enclosure. An alternative is to use a shorter bulb in combination with a heat lamp while leaving the rest of the cage shaded. These bulbs emit UVB light at an average effective distance of 12–20 inches, depending on the brand and percentage of emitted UVB. It is generally recommended that animals should not be abe to get any closer than within 3– 4 inches of bulb’s surface. Bulbs need to be replaced every 6–12 months according to manufacturer’s recommendations.
T5 High Output Linear Fluorescents
A high‐output light is a T5 bulb (16‐mm or 0.6‐inch diameter) that requires a hood with a T5 fixture. T5 bulbs are more efficient and provide a higher amount of UVB than T8 or compact fluorescent bulbs. In theory a T5 10.0 bulb produces a higher amount of UVB than a T8 10.0 or compact fluorescent. It is worth mentioning that Zoo Med Laboratories Inc. produces a T8 10.0 bulb labeled high output but their T5 10.0 bulb is actually a much stronger bulb and is considered as a true high output for our purposes. These bulbs emit UVB light at an effective distance of 12–36 inches, depending on the brand and percent of emitted UVB. While it is generally recommended that animals should not have the ability to get any closer than within 3–4 inches of bulb’s surface, this distance may actually need to be longer for high output bulbs. They must be replaced every 9–12 months according to manufacturer’s recommendations.
Compact Fluorescent
Compact fluorescent bulbs can be fitted into any incandescent fixture that would fit a household bulb but a reflective or reptile‐specific fixture is preferred. The light is focused over a smaller area so there is less scattered radiation. For this reason, it is possible that a 10.0 compact fluorescent may actually emit a higher UVB output than a 10.0 linear fluorescent over the same area. It is usually recommended to place these bulbs next to the heat lamp so the reptile gets UVB exposure while basking. All other properties are similar to the linear fluorescent bulbs although some may think of these as being less effective and being “weaker” in the UVB spectrum.
Mercury Vapor Bulbs
Mercury vapor bulbs have been successfully used by breeders and zoological institutions for decades but have just recently made it into the mainstream exotic pet market. Their external appearance is that of a floodlight and they are commonly found as a self‐ballasted variety in the pet trade. Self‐ballasted bulbs can be fitted into an incandescent fixture that would fit a household bulb but a reflective or reptile‐specific fixture is preferred. A fixture with a ceramic base is also recommended because of the high amount of heat the bulbs produce. The light is focused over a shorter area so there is less scattered radiation. Their UVB output is based on the wattage of the bulb and the fixture should accommodate the appropriate wattage. Their effective distance is 12–36 inches. There are also some high‐output bulbs with an effective distance of up to 8 feet. A major advantage is the production of heat and a stronger UVB output compared with all other bulb types. In the hands of inexperienced individuals, however, these bulbs could be detrimental to reptiles. If placed too close to the animal, they could cause thermal damage. There is also a concern about overexposure to UVB, which could cause eye damage and even neoplasias. It is imperative that these bulbs are used properly; the author only recommends them for zoological institutions and advanced hobbyist who understand the principles of UVB exposure in reptiles. They must be replaced every 3–‐12 months, depending on manufacturer, model, and use.
METAL HALIDE BULBS
Metal halide bulbs are becoming more commonly available. They produce heat, UVB, and infrared light. Their beam is very narrow compared to all other bulb types which means that they can provide very high UVB levels but over a narrow area, which may be a positive feature in some enclosures (e.g., tall enclosures) but dangerous in others (e.g., short enclosures). These bulbs require external ballast and a properly rated fixture for operation and safety. Their use is best reserved for advanced hobbyist familiar with the principles of UVB lighting.
UVB REDUCTION
As previously mentioned, the type of material present between the bulb and the animal is an important consideration when selecting a UVB bulb. Most glass and plastics are known to block or filter out UVB radiation and are not recommended. The ideal scenario is one of an open‐topped enclosure with no material present between the bulb and the animal. While this is a possible application for chelonians, it is not feasible when housing snakes and some lizard species. A study by Burger et. al. revealed the UVB attenuating effects of common materials used in reptile enclosures and provides a sobering insight into the use of UVB bulbs (Burger et al, 2007).
The type of material, aperture of the openings, thickness, and reflective properties can all influence UVB attenuation and can significantly decrease the UVB exposure of reptiles. Most reptile enclosures have a screen or wire mesh top to keep the animals from escaping. Some of these screens may reduce the UVB light exposure to the animal by as much as 50%. To put this in perspective, if a reptile had a 10.0 linear fluorescent bulb, the effectiveness of that bulb might be reduced to that of a 5.0 by the time the light passes the screen and reaches the animal. This is why knowing the type of screen material is critical when selecting a bulb. A general recommendation is to select a screen with the largest aperture possible and with a mat or painted finish that will reflect less light.
SELECTING BULBS BASED ON SPECIES
There is a common trend toward make recommendations of bulbs based on the species with which it will be used. The principle behind this makes sense but in practice it is flawed. The thought is that
