Arc light spectrum with various filters.

Arc light spectrum with various filters. White light from the carbon arc passes through a slit and is sent through a diffraction grating, creating a full spectrum. Various colored filters can be inserted in the beam (red, green, blue, magenta, cyan, yellow, etc.) For instance, white light passing through a cyan filter and a magenta filter, gives blue. White light passing through yellow and magenta filters gives red. Through yellow and cyan gives green. No light passes through yellow and cyan and magenta filters. Note: the lenses focus the spectrum on the distant screen. (The magenta filter basically allows all the visible spectrum through, except yellow. The cyan filter allows yellow, greens and blues through, but no red. The yellow filter allows reds, yellows and greens through, but no blue.)