Do Freshwater Turtles Need Light at Night?

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.

  1. 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 their turtles in indoor aquariums and use artificial UV lights to provide their pets with access to vitamin D. Because these lights produce less UV light than sunlight, they must be left on longer every day to ensure a turtle has adequate access to vitamin D. Turtles need a minimum of 10 to 12 hours of light from a bulb each day, and some bulb manufacturers recommend using their bulbs for as long as 18 hours each day. Turtle owners can provide their turtles with ample UV and a period of darkness by placing lights on a timer and taking their turtles outside in natural sunlight for 30 minutes each day.