I use blue lunar light type LED's, and I have the timer shut off the main lights and turn on the LED's for a half hour before shutting everything off. I don't think it's necessary, but my fish seem to like it. It keeps them n a routine schedule, and they seem to really calm down and get ready for nite nite time once the LEDs come on. I know I'd be ticked off if my house suddenly went black at night with no warning, but then again I'm not a fish.