Things to know

• This is also called a CdS photocell (Cadmium Sulfide)
• Don't forget that d*mned pull down resistor (depending on your schema)! And don't be cheap, go for the 10 kOhm !

Using the wavelength response as a cheap color sensor

The CdS varies its resistance according the amount of light received, but also according the wavelength. You can turn that to a poor man color sensor!
See the sample project here :

• Sample http://www.instructables.com/id/Using-an-RGB-LED-to-Detect-Colours/
• My version cameleon

CdS without a CdS

• Using a led, one can sense light : cheap and ROHS compliant:
  • http://provideyourown.com/2011/cheap-alternative-for-hard-to-find-cds-light-sensor/

Pictures / Schema

And don't forget that ####### pull down ! (schema and photo are courstesy of Sparkfun)

Links

Shopping

• Photocell http://www.sparkfun.com/commerce/product_info.php?products_id=9088

Tutorials

• Good explanation on pull-up/down with sensors (japanese) http://kousaku-kousaku.blogspot.com/2008/06/blog-post.html