Freshwater turtles require UV light to maintain healthy shells.
Freshwater turtles, including red-eared sliders, river cooters and painted turtles, are among the most popular reptile pets. They require calcium in order to maintain healthy shells and must have access to vitamin D from either sunlight or artificial UV bulbs to properly metabolize calcium. This need for light is the source of much confusion among turtle owners, and many mistakenly believe their turtles need constant light.
Circadian Rhythms
Most freshwater turtles are diurnal, which means they are primarily active during the day and sleep at night. Turtles in captivity take cues from their environment to determine when to sleep and when to be active. Consequently, freshwater turtles should have a period of darkness in order to maintain healthy circadian rhythms. Turtles that are exposed to light constantly or at unpredictable intervals may become lethargic or ill.
Heat Lights
Most freshwater turtles thrive in water temperatures slightly above room temperature, ranging from 70 degrees to 80 degrees Fahrenheit, depending upon the species. Turtles living in water below 60 degrees Fahrenheit normally stop eating. Many turtle owners ensure that their pets' water temperature is adequate by placing a heat light above the aquarium. Though turtles should not be constantly exposed to light, they must be maintained in stable temperatures, so heat lights pose a problem. A better option for providing heat is to use an aquarium heater. Some pet stores also sell heat bulbs that produce heat but no light.
Night Lights
Some turtle owners, concerned about the effect light has on their turtles' circadian rhythms, believe turtles should be kept in total darkness at night. This is not necessary. Turtles in the wild are exposed to periodic bursts of light as well as low-level lighting from stars, nearby houses and cars. Thus turtles living in captivity are not harmed by nightlights, televisions and other minor interruptions to nighttime darkness.
Ultraviolet Light
Most turtle owners keep