Right now at my stage, I kind of get how to set up a lighting condition inside a painting, however, it has always puzzled me the range and effects of the light, the difference of the lights (such as lights from fire place, candle flames, or from light bulb on a football field.)

I have no problem spotting the light when I am drawing or painting from life. I have problem however... when it comes to painting things that doesn't exist. Like a light saber.... for example. What should I use to reference for those kind of fantasy lights?

Do I simply make up my own rules depending on my preference?

Should I take notes, make list of every kind of lights in different situation? (if there's book reference I would be glad to hear recommendation.)

Or is there tips and formula I can follow for this kind of things such as the edges talk discussed here: http://www.conceptart.org/forums/showthread.php?t=51913

My thanks to those who will take a look at this and take the time to answer my puzzle.