That's a top idea - print out a set of 16 strips on laser printer transparency and cut them out. My suggestion though - if the film has to move, you need 2x length of the film clearance under the board, for all the way up and down. Mount the film stationary, and attach the LED/LDR pair to the fader handle. Probably a little simpler to construct too. Dust, smoke, fading or aging of the film could be a problem. Now who's got an idea for a homebrew motorfader?