Here is a model of a "force table
spectroscope". Consider the top figure to the left - a top view
of the spectroscope - the light comes in from the North, hits the
diffraction grating, and then the light separates into the various
colors. We are following 4 colors (approximately the spectrum of
Helium) : Red = 677 nm, Yellow = 594 nm, Green = 500 nm, and Blue =
456 nm. You can see those beams radiate away from the diffraction
The top figure shows a top view of the "spectrometer"
- the angles for which the light beams would exit the diffration
grating (the black horizontal rectangle).