Frances M. Baines MA VetMB MRCVS
(A brief resume of my presentation to the British Chelonia Group seminar on 8th March 2008)
First I would like to thank the Chairman and Committee of the BCG for inviting me to speak at the Spring Symposium, and also for making me so very welcome and providing a most enjoyable weekend.
My presentation was entitled, "Everything Under the Sun - Natural and Artificial Lighting for Chelonia."
To a reptile, sunlight is life. Chelonia are quite literally "solar powered"; every aspect of their lives is governed by their daily experience of solar light and heat or the artificial equivalent, when they are housed indoors. Careful provision of lighting is essential for a healthy tortoise or terrapin in captivity.
The spectrum of sunlight includes infrared, "visible light" (the colours we see in the rainbow), and ultraviolet light.
Infrared is of course "the warmth of the sun". Chelonians absorb infrared, radiation extremely effectively through skin and carapace. The heat transfer to the rest of the body is as efficient as any solar panel, and they retain heat well, so once warmed by sunlight, they can be fully active at surprisingly low air temperatures.
Visible light is of course essential. Most reptiles have extremely good colour vision. The eyes of red eared sliders, for example, have cones responding to not only all the colours we recognise, but also higher wavelength UVA (from 350nm) and low wavelength infrared, (up to about 750nm); these are almost certainly additional colours in the turtle's rainbow. "UVA colour" is especially important to many reptile species in recognising conspecifics and even food items.
The sun’s light also has effects unrelated to conscious vision. Information from the eyes about the intensity of the light, its colour and its polarity travels to other parts of the chelonian brain, and there are even areas of the brain itself which respond directly to the glow of sunlight which reaches through the skull. The length of day and night, the position of the sun in the sky and the amount of blue in the sunlight all give precise information about what time of day and what season of the year it is, and in response, the tortoise or terrapin adjusts its activity levels and its daily and seasonal behaviour (including the reproductive cycle and preparation for hibernation), including its thermoregulation "set points" and optimises the function of its immune system.
There is no artificial lighting system in the world that can provide the full spectrum and intensity of natural sunlight (from 3,000 lux five minutes after sunrise, to over 150,000 lux at mid day, even in the UK, in summer) let alone mimic its subtle changes in colour as a day progresses, or its movement across the sky. For these reasons alone, the more natural sunlight a chelonian sees, the better.
Sunlight also has direct effects upon exposed skin. Tortoises and terrapins can often be seen basking with neck and legs fully extended. They are absorbing both visible and ultraviolet light through their skin.
The ultraviolet light in sunlight has a direct effect upon the immune system in skin and may also stimulate production of beta endorphins (giving sunlight its "feel good" factor); but it is best known for its role in skin synthesis of vitamin D3. For this to occur, the sunlight must contain UVB in the wavelengths from 290nm to about 315nm. Most glass and plastics block these wavelengths, and they are also partially blocked by the atmosphere so the sun must be fairly high in the sky for significant amounts of UVB to be found in the sunlight. In the UK, however, there is plenty for vitamin D3 synthesis from mid morning to midafternoon in sunshine from April to September, and from early in the morning until late afternoon in midsummer (mid May until late July).
From April to September, then, chelonians even tropical species will benefit from outdoor enclosures whenever the ambient temperatures are suitable. Daytime shelters such as small greenhouses or even modified cold frames can be glazed with special UV transmitting acrylic to ensure the "outdoor" tortoise always benefits from UVA and UVB. Trade names include Perspex, Plexiglas and Lucite but it is vital to order sheets which have not been formulated to block UV rays.
Chelonians kept indoors need excellent levels of full spectrum lighting which must include UVB and UVA. This cannot be supplied by just one type of lamp; it is necessary to "mix and match".
UVA and UVB can be supplied by good brands of fluorescent tubes and mercury vapour lamps sold for reptiles. However, these are usually deficient in red and yellow light, with a predominance of green, blue and purple. The fluorescent tubes also provide only comparatively dim light and very little heat.
Ordinary tungsten or halogen "household" flood lamps provide excellent heat and light at a basking spot, but their light is predominantly red and yellow, is very deficient in blue and UVA, and has no UVB These therefore complement UVB reptile lamps extremely well. They also allow for accurate temperature control since they can be controlled with a dimming thermostat. They can be used to produce a primitive "dawn and dusk" effect, too, since at these times the light is more golden and has little or no UVB. Timers may be used to switch the incandescent lamps on a short time before the UVB lamps, in the morning, and off shortly after them at the end of the day.
Because vitamin D3 synthesis occurs only in warm skin exposed to UVB, ideally the UVB lamp needs to be over the basking spot where the tortoise or terrapin basks with legs and head extended. To protect the eyes from glare and excessive UV, all light sources should be above the reptile's head, not to the side, and none should be closer than 4 6 inches from the reptile. Many UVB lamps have minimum and maximum recommended distances; these must be carefully observed. It is vital to check the temperatures which will be reached under a basking lamp, and to take into account the height of the chelonian carapace when doing this.
UVB fluorescent tubes produce diffuse, low levels of UVB resembling outdoor shade on a sunny day. These are ideal for species which do not bask in sunlight, such as some forest shade dwellers; or for small enclosures where the heat from mercury vapour lamps would cause problems with the thermal gradient.
Brands vary widely but quality tubes emit light with a UV Index between about 0.5 and 1.0 at 12 inches (the usual maximum distance suggested.) Fluorescent tubes with spectral output in the UVB range resembling that of sunlight include the ZooMed Reptisun 5.0 and 10.0 tubes, the Arcadia D3 and D3+ Reptile Lamps and the JBL Solar Reptil Sun.
There are numerous rumours about decay in UVB fluorescent lamps. The truth is that all brand new lamps "burn in" they lose from about 10% to 35% in the first 100 hours of use. Then the rate of decay slows greatly; by 3 months, decay is so slow that most tubes we teste lost only another 15% to 20% of their UVB output over a whole year of use. If a lamp's output is good after 3 months' use, it is unlikely to need replacing before I year.
UVB compact fluorescent lamps also produce diffuse, low levels of UVB at basking distances but at close range and/or if reflectors are used, the light and UVB may be rather intense, making good positioning quite difficult.
Probably because these operate at higher surface temperatures, they decay more rapidly. Most tubes we tested appeared to need replacement after 6 months' use.
Compact lamps with spectral output in the UVB range resembling that of sunlight include the Arcadia D3 and D3+ Compact Reptile Lamps and the Lucky Reptile Compact UV Sun.
Mercury vapour lamps vary in quality and UVB output; several types are on sale. Cheap "spot" lamps with clear glass faces may produce extremely narrow, hazardous beams of very intense UV light and are best avoided.
"Flood" lamps have much wider beams with varying amounts of UVB. Well known brands include the ZooMed Powersun, which produces diffuse, fairly low levels of UVB resembling outdoor shade on a sunny day, with UV Index between 1.0 and 2.0 at 12 inches distance.
For chelonians which bask in bright sunlight, "narrow flood" lamps such as the ReptileUV MegaRay or T Rex Active UV Heat Flood, both made by Westron in Canada, may be more suitable since they create a zone of bright light and LTVB directly below the lamp resembling a small patch of sunlight. The UV Index from I 00W versions of these lamps is between 4.5 and 7.5 at 12 inches distance.
Mercury vapour lamps vary in how rapidly their UVB output decays. The Westron lamps seem to decay slowly but steadily, and the UVB output is likely to be adequate for a full year. The output from a ZooMed Powersun we tested for a year initially decayed considerably more than the Westron lamps, but the rate of decay then slowed more dramatically so at the end of one year, the overall decay for both lamp types was similar.
Finally, metal halide lamps are rapidly gaining a place in, or rather over, the vivarium. These are High Intensity Discharge (HID) Lamps which, like mercury vapour lamps, cannot be used with a thermostat and are most suitable for large enclosures. The "Daylight" versions with colour temperature between 5500K and 6500K are the closest to sunlight.
Most metal halides are manufactured for use over aquaria, for plant growing, or for industrial lighting and these lamps do not emit UVB. However, metal halides emitting UVB, designed specifically for reptiles, are now under development and early test results look promising. Metal halides produce a far more intense white light with a much higher quality spectrum, across the whole range for visible light, than either mercury vapour lamps or household incandescent lamps. They do however require an external ballast and positioning them is crucial, since at close range the light is extremely intense and the lamp should not be looked into directly.
It is unlikely that it will ever be possible to improve upon nature; most chelonians will do best when provided with lighting as close as possible to that they would experience in their native habitat. With many species this will include basking in natural sunlight for at least part of the day, whenever this is possible. When this is not possible, there are now many combinations of lamps, bulbs and tubes that will, used with care and sensitivity, go a long way towards meeting the needs of turtles and terrapins in captivity.