Turtles need several hours of exposure to natural sunlight every day. This
helps them synthesize vitamin D3. If you keep your pet outdoors, and there
is sun and shade available in the enclosure, you don't have to worry.
If your turtle is indoors all the time, you have to provide a source of
full spectrum lighing or supplements.
There are constantly new lights on the market, and there is a lot of
discussion on this issue.
There are 3 bulbs on the market that produce significant
levels of UVB: Zoo-Med's ReptiSun 5.0, ESU's Desert Sun 7.0, and Reptile
D-light (usually available only by mail order). All must be replaced every
4-6 mos (timing depends on which research you think was most elegantly
designed, but they all agree on the brevity of the useful life) because a
coating builds up on the inside of the bulb which blocks the UVB. Also, they
must be no more than 12" (or 14", or 18", again depending on whose research
was best designed) from the animal in order to affect blood calcium levels.
* Some of my turtles enjoy a walk outdoors every once in a while. Watch your
turtle at all times, so he won't get hurt or lost.Turtles can get lost
very quickly, if they want to.
* Turtles need a basking light. The silvery shop lights from the hardware
store are great. Place it on a screen top or hang if (high enough that
the turtles cannot touch the bulb). I find that a 60W bulb is about the
right strength. I tend to use a 40-60 Watt bulb in summer and 75W in winter.
* The lights should be on between 10 and 14 hours a day, depending
whether you use a yearly cycle, or not, and depending on where your
turtle comes from.