Beamwright software is a useful beam spread calculator.
Most of Beamwright is pretty self-explanatory: The general concept is to set up a situation with a light hanging at some trim above the floor at some distance horizontally away from a person you want to light. Fill in the size of the area you want to cover and what height you want the center of the beam focused on, and then ask Beamwright to show you how various lights perform under that situation.
Programmers Calculator that supports full precedence, large range of operations
