Optimum (previously known as Grasslin, and still made by them) segmental timers are quality, multi-use timers used in grow rooms to control appliances without the laborious need to do it manually.
They are a must-have for most growers - used to control light cycles, irrigation frequency and ventilation equipment accurately - all very important for good, consistent results. The 24 hour period is split into 15 minute segments which can be positioned to either 'on' or 'off' for full daily control of your environment.
They are limited in the electrical load they can safely handle - for up to 600W of HID lighting use a Heavy Duty Timer or for more use the Maxiswitch 2-way controller.