What affects the light intensity and light output geometry?

These are some of the factors I brainstormed that goes into the functionality of a spotlight:

1) Light output of the light source (measured in luminous flux, if I recall correctly)
2) The reflective potential of the reflectors surrounding the light source
3) The geometry of the reflectors; the shape of the reflector is always parabolic
4) The position of the light source from the focus of the parabolic reflector; more generally, the position of the light source from any reflector


I'm going to try to design a DIY lamp so I'm brainstorming all of the available constraints of the project.