Where is the best location for a light bulb filament to be placed in a spotlight, when using a concave mirror? It makes the most sense to put it at the focal point of the mirror if you want parallel light beams but are you supposed to have parallel light beams when you use a spotlight? Or do you want the beams to diverge slightly so the light covers a larger area? I also read that in some slide projectors, the light bulb is placed at the center of curvature.. is this the same thing as radius of curvature? Or are they meaning focal point? I'm just a little unclear.. Thank you in advance for your help!