I'm not sure on how many laptops this works on, but on my early 2008 MacBook Pro, when the computer is asleep with the screen down, the pulsating sleep light is quite bright. In the older G5 and first intel iMacs (and I'm not sure which other models), when the computer is asleep in a dark room, the light dims right down.
The hint is to put your computer to sleep using the Apple menu, or the power button if you have it set up that way. Then leave the screen open and allow the computer to make use of the light sensors in the speakers. This will then make the flashing light dim. It seems that closing the screen turns the light sensors off, and the light shines at its normal brightness.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080610184610810