First of all, you need to find a room with a door you can close, so it can be totally dark.  No night lights or glowing clocks!  Make sure the room has a lamp with a regular light bulb in it.  This is important!  The trick won't work with a fluorescent bulb.

   You have to be able to flick the light on and off in a second.  A wall switch will work best, a pull-chain is okay, and a turn-button is the slowest.  Once you know what to look for, you can try whatever you have and experiment.

   When it's night, go into your bedroom and look around.   Pull out your nightlight and turn your clock face down on a towel.  Close the door and switch out the light.   If the room is totally dark, everything's okay.   If you see any light at all, turn the light back on, fix the problem, and turn the light off again.

   Stay in the dark for about five minutes to let your eyes adjust to no light.  Now, get ready!  Look across the dark room at something you know is there.  Stare at it in the dark and flash the light ON then immediately OFF.

   Like a flash from a camera, you'll see the bright room, then darkness again.  Keep staring without moving your eyes!   In a moment, the room will seem to glow as the after-image from the flash registers in your brain!

   If you can keep your eyes motionless, the effect will last several seconds longer as it slowly fades away.  This is very cool and you can have fun with it!  Hold your hand in front of your face when you flash.   It's very weird to move your hand after the flash and still see it frozen in front of you!

   Try this with your friends at a sleep-over.   You could tell ghost stories while you let your eyes adjust to the dark!   Be careful, one of them might be standing right in front of you when you flash the light!  Let me know how it works for you by e-mail!  Have fun!