The grating (DVD) bends the light as it separates it into colors. So the grating has to be at an angle to the light coming from the entrance slit. Note the ~45° angle of the web cam and DVD piece in the photo in step 5. So just rotate your webcam and it might work. The concentric grooves on the DVD should be perpendicular to the incoming light.

Hmmm... when I do this, I can get green and blue lines running the right way - until I close my box. Then they're gone completely and still all I can see is the white light.

This is your box:

|o> |=| |__||

Your pointing your camera directly at the double slit - you instead need to point it at the black of the wall (at a 45° angle as mentioned above) so its like this...

|O」..........|=| | * .| | |________||

This ^ - is where you point to get the rainbow. :)

Hope this ASCII doesn't screw up. Amy

Hmm, can you upload a photo of the box with the new angled layout?

Here you go. I've tried a variety of angles, and I can see some emmission spectra, but once I close the box it goes away and all I can see is dark or possibly the line of light moving in the box. I'm certain I'm doing something wrong, I just don't know what. :-(

That looks like a good arrangement. The DVD grating might have to be rotated. The circular grooves in the DVD (concentric to the outer edge) should be vertical in that photo.

THANK YOU!!! I'm terribly impressed that you could tell the circular grooves were horizontal. I'm going to have to tinker a little bit to make the spectra exactly linear where I want it, but I think this fixed it!

For anyone else looking for the solution - I basically I had two problems. One, my webcam was not angled properly. It shouldn't be looking directly at the light source but angled 45° from it. Two, my dvd needed to be rotated - it was 90° off.

Thanks to everyone for their help!