Most of this literature comes from this source – https://www.jzar.org/jzar/article/view/150/89. The author, Fran Baines, is also an avid reptile keeper, herself, and available for questions on the facebook group, “Reptile Lighting.” I do not claim to be an expert in lighting, so please contact Fran Baines for the best advice. https://www.facebook.com/groups/ReptileLighting/
Lighting is a very serious consideration for the health and longevity of your tortoise. Zoos have done studies showing that when sea turtles are confined fully indoors, their vitamin D levels will start to decline after 4-5 months and will continue to decline. After 6-8 years kept indoors, indoor turtles had only 15% of their healthy level (compared to those outdoors) (Hugh et al., 2009). Considering the animals studied were kept in zoos, under ideal indoor conditions, and their Vitamin D levels still continuously dropped, the average keeper can never justify keeping a tortoise indoors its whole life! Please consider this when purchasing or adopting a tortoise.
In our climate, however, we know we can not keep tortoises outdoors year round. For the winter season, we must try to provide them with the most suitable artificial lighting instead. The quality of light is very important for reptiles for normal behavior and reproduction. Lighting in the UVA wavelength (visible light, 320– 400 nm) is generally provided by most light sources. UVB lighting (290–320 nm) is required for cutaneous development of vitamin D3, in turn allowing absorption of calcium from the intestinal tract. Specific wide-spectrum fluorescent lights with ultraviolet irradiances between 290 and 320 nm are hypothesized to ensure vitamin D activation (Boyer, 1994). Tortoises will benefit greatly from time outside in natural sunlight, because no artificial bulb can fully replicate the sun (Wilkinson, 2015).
There are 3 main types of UVB bulbs commercially available to reptile owners: fluorescent tubes, mercury vapor bulbs, and compact fluorescent bulbs. Fluorescent tubes are available with different output levels of UVB, the higher levels (10.0) being more suited for basking species, such as sulcatas, leopards, russians, and greeks. The lower levels (5.0) are more suitable for species that originate from a mostly shady landscape, such as forest-dwelling species like the red/yellow foot, elongated, hingeback. They do not produce heat, and must be accompanied by a heating source, such as a ceramic heat emitter (CHE). CHE’s are also a great alternative when night-time heat is needed because it does not produce any visible light. Mercury vapor bulbs (MVBs) are considered an “all-in-one” or a “combination” bulb because they provide heat, UVA, and UVB all in one bulb. These bulbs are one of the best bulbs on the market for mimicking the natural sunlight, however, quality will vary from bulb to bulb or from brand to brand. Purchasing a solar meter for measuring UVB output is important when using MVBs. Compact fluorescent bulbs produce very little UV output and also do not produce heat. In general, this type of bulb is not very useful for a basking species (Wilkinson, 2015). Additionally, when these bulbs first became available, there was a high incidence of photokeratoconjunctivitis and photodermatitis associated with their use caused by a problem with the glass in the bulb allowing more shortwavelength UV radiation to penetrate (Gariner et al., 2009) Since this problem was discovered, however, it has largely been resolved. Even if these problems have been resolved, these bulbs are not an adequate source of UVB.
Whichever lamp you provide, it is important to refer to UV index iso-irradiance charts for your particular lamp (see figure below) to know the proper distance to place your lamps, or to purchase a UV-index reader to measure the output yourself.
Photoperiod, or the amount of time the lights are on a day, is also very important because this cues the animals as to seasonal changes. For instance, if Russian tortoises notice the day lengths are shortening, they will begin to eat less, dig deep burrows, and sleep often as they prepare for hibernation with the oncoming winter season. Please refer to the chart below (exert from table in Bains et al., 2016) for information regarding the native zone and most appropriate photoperiod, temperatures, etc.
Bains, F. et al. (2016) How much UV-B does my reptile need? The UV-Tool, a guide to the selection of UV lighting for reptile and amphibians in captivity. Journal of Zoo and Aquarium Research. 4(1): 42-63.
Boyer, D.M. and Boyer, T.H. (1994) Tortoise Care. ARAV, Vol. 4, No. 1.
Gardiner, D.W., et al. (2009) Photodermatitis and photokeratoconjunctivitis in a ball python (Python regius) and a blue-tongue skink (Tiliqua spp.)J Zoo Wildl Med, 40, pp. 757-766
Hugh Purgley, et al. (2009) Vitamin D3 in Captive Green Sea Turtles (Chelonia mydas). Chelonian Conservation and Biology: December 2009, Vol. 8, No. 2, pp. 161-167. https://doi.org/10.2744/CCB-0765.1
Steams, B.C. (1985) Captive husbandry and propagation of tortoises. Proc Northern Calif Herp Soc and Bay Area Amphibian and Reptile Soc 1985 Conference on Captive Propagation and Husbandry of Reptiles and Amphibians, pp 113-129.
Wilkinson, S.L. (2015) Reptile Wellness Management. Vet Clin Exot Anim, 18: 281-304.