In the wild, reptiles function according to natural rhythms, such as hunger and temperature. But did you know that exposure to light can completely change how your pet behaves? A reptile’s lights do more than simply tell it when to wake up or go to sleep. To understand how your lighting setup is working for (or against) your pet, you’ll first need to grasp the concept of a photoperiod and how it changes reptiles on a biological level.
What Is a Photoperiod?
A photoperiod is the number of light and dark hours in a day. In nature, the photoperiod changes along with the seasons; that’s why days are shorter in winter and longer in summer (or vice versa, depending on where you live). Thus, animals can intuit the time of day and time of year based on the photoperiod, which in turn influences their daily behaviors and reproductive choices.
Because reptiles rely so much on the photoperiod, the light schedule you keep them on matters, even when your temperature and UVB levels are otherwise correct. If you turn your reptile’s light on at 7am and turn it off at 7pm, that’s a 12-hour photoperiod.
What’s Happening in Your Reptile’s Body Under Light
You might think that all of these “calculations” about season and behavior are happening in the brain, but your reptile’s body is also undergoing changes as a result of light. Among the most important factors in the photoperiod is melatonin. You might have heard of melatonin or even use it yourself in the form of small capsules, which are intended to help you fall asleep. In reality, its purpose can be more broadly described as a timing signal, giving the body information about when it should be resting or awake.
In box turtles, researchers found that when they used an 18-hour day, the turtles only produced melatonin to last for about 4.5 hours. However, if they tried an 8-hour day, the same turtles produced around 11 hours of melatonin. In other words, the turtles are adjusting their body chemistry according to light production so that they could sleep while it was dark. Even if you keep a heating element on at all times, your reptile relies on light as part of its biological equation.
Interestingly, this remains true even when reptiles were blind. Fence lizards, for example, continue to respond to light-dark cycles even after the animals can no longer see. This phenomenon is called extraocular photoreception (an ability to understand light without using the eyes).
Does Day Length Matter?
Every reptile species is different, so the right photoperiod for your pet will depend on what type of reptile they are. In general, the photoperiod sets a reptile’s daily schedule because reptiles have circadian rhythms that, like ours, are based on a roughly 24-hour cycle. For a diurnal reptile (one active during the day), day length can help them to plot out when to emerge from hiding, when to bask and rest, when to forage, and when to sleep for the night. As a result, reptiles that don’t receive an appropriately long photoperiod might lose their appetite, as there’s not enough time within their provided daylight hours to trigger the impulse to forage or eat.
At the same time, a shorter photoperiod also means less activity in general. Less activity is tied to needing fewer calories, which further contributes to changes in appetite.
Another big factor for many keepers when considering day/night cycles is reproduction. For many species, the young have the best chance of surviving during specific parts of the year. Reptiles are working against their own species interests if they have their babies during sparse seasons when food and shelter are less available. Thus, the photoperiod can help them determine the current time of year, which in turn dictates which phase of reproduction they might be in. The photoperiod, in this context, mostly acts on the hypothalamic-pituitary-gonadal axis (the part of the reptile’s hormonal system that focuses on reproduction).
Melatonin plays a role here, too. Melatonin is linked to gonadotropin-releasing hormone (GnRH), which in turn regulates changes in other features you’re probably more familiar with when it comes to reproduction: testosterone, estrogen, ovulation, courtship and mating, and so on.
What Happens If You Leave the Light on Too Long?
By the sounds of things, giving your reptile as much light as possible might seem like a good choice. It’s giving them a longer period in which to be active. However, lights help to keep your reptile’s biological rhythms in line, and constant or unpredictable lighting can disrupt those rhythms.
Darkness is just as important as light. Without enough darkness, your reptile might be consistently tired, which can lead to health issues, decreased appetite, reduced activity, and more. Whether or not you change your lighting according to the seasons is a personal choice and should be based on your specific species’ natural habitat. Just remember that those lights are there for your reptiles, not for you. Consider what’s best for your pet when making a plan!