This timer is very adaptable for many different aplications. If you look around the perimeter, you will see 48 small levers. These levers represent 30 mins. segments. Start by lifting all of the levers up. For the time that you want the timer to be "on" push the lever down. For the duration of the time that you want the light on, all levers should be down. The light will change state each time there is a difference in the lever position.I use the timer for items other that lights. For example I have my air cleaners set to be on 1 hour and off 1 hour. To accomplish this, the levers will be set to have 2 up and then 2 down around the entire perimeter. I also use them on the glade air fresheners that seem to run out too fast. I have set the levers for 30 mins on then 1 hour off. To accomplish this, the lever states are set to 2 up and 1 down all around the timer. You will have to rotate the timer away from the current time, in order to set the lever in that area. after all levers are set, rotate the timer to the current time.These are just a couple of examples. But you can see you how adaptable the timer is.