Similar to lighting, a decrease in temperature might be needed for the simulated night periods, thus keeping living species healthy. Such variation need to be coherent to those found in the natural habitats of the species. Thermo-control systems are often used to regulate light cycles and heating, as well as humidity (coupled to built-in misting or rain systems). Light-dependent resistors or photo-diodes connected to the lighting are frequently used to simulate daytime, evening and nighttime light cycles, as well as timers to switch lighting and heating on and off when necessary.