Check out DoWatts DVD Spectra instructable.
Step 1: Supplies
*Single edge rasors or a breakable thin rasor blade work well. For a children's safety version, use the opposite edges of a credit card cut in half. It will save you a lot of money!
*The LED's are fun to observe as is a compact flourescent light. The laser pointer is dangerous and should be used with care and only to illuminate a translucent plastic bag covering the slit.
- Any CD that you don't mind damaging
Step 2: Construction
A hole 10 mm x 20 mm is cut far enough from the front edge to allow taping two razor blades in place 1 mm apart or less. A viewing hole 25mm square is cut 95 mm from the slit. This hole can be slightly oversize for ease of viewing. The light guard is not essential but it is definitely helpful. Hot glue was used in much of the construction. Again, it is not essential but made things easier.
Step 3: Cereal Box
I welcome links to similar projects to be posted here.