If you're just looking for something to experiment with, Radio Shack has a multi-pack of photocells for a couple of bucks (276-1657). Not so tightly spec'ed as some others, but they make up for it with quantity. Here's the RS data sheet...<p>
RS 276-1657 data sheet.htm<p>Photoresistors have a frequency response and reaction time similar to that of the human eye. They were a favorite of Forrest Mims III, who used to write for one of the hobbyist magazines a while back. He's currently working with GLOBE, an international science education project. Back when he was writing for Modern Electronics, I used to flip the magazine open to his articles first every month. His explanations made the craft seem easy, and he made it fun. No higher praise can be given to a good science teacher.<p>Good luck.
Chris<p>[ October 07, 2003: Message edited by: Chris Foley ]</p>