First and second order transmission gratings, with arc lamp.

First and second order transmission gratings, with arc lamp. White light from the carbon arc passes through a slit and is sent through a transmission diffraction grating, creating a full spectrum on a projection screen. The 14,438 line-per-inch grating has the blazes cut so that most of the light is concentrated in the first order. The 2,100 lpi grating has the blazes cut so that most of the light is concentrated in the second order. Note to setup people: The second lens is positioned so that the image of the spectrum is focused on the screen.