Reflection grating with arc lamp.

Reflection grating with arc lamp. White light from the carbon arc passes through a slit and is bounced off of a reflection diffraction grating, creating a full spectrum on a projection screen. The 10,000 line-per-inch grating has the blazes cut so that most of the light is concentrated in the first order. This reflection grating is brighter than equivalent transmission gratings. Note to setup people: The second lens is positioned so that the image of the spectrum is focused on the screen.