Timers are an essential part of your every day reptile supplies. Reptiles have an internal clock, called a circadian rhythm that knows the season and the time of day. Keepers control the ‘time of day’ by deciding what time the lights come on and what time they shut off. The best way to guarantee that their lights come on at precisely the same time every day is to put them on a timer. The timer can be programmed to turn the lights on and off at certain times of the day or night. Some will also have at least one plug that is always on. There are analog timers that turn the lights on and off at the same time each and every day, and there are digital timers that can be programmed by day of the week. Typically diurnal reptiles require longer summer days and shorter winter days, which is achieved by adjusting timers from 14 to 10 hour days. Summer days are 14 hours long, decreasing to 12 hours in the fall, 10 hours in the winter, and back up to 12 hours in the spring and finally up to 14 hours in the summer. Even without adjustment of the lighting reptiles will often seem to want to go to sleep earlier in the day as the days get shorter.