I realize that those of you who know me as a preacher may mistake the title of the post. But this is about finding actual light, not the spiritual kind.
In film, hours and hours are spent adjusting lights for specific moments, and then striking them for new lighting. A film actor is given a very specific spot to stand, their `mark` so that they get in the proper light. But on the stage, we preset lights and then leave them. Oh yes, we now have some high tech lights that move and adjust, but those are limited, as is follow spot use. For the most part, stage lights are there to light the scene, you as a thinking actor are responsible for finding your own light.
Finding your light is simply a matter of practice. Most stage lights shine downward at an angle. You can actually feel the light falling on your face. Take some time and have a stage light turned on, and practice walking in and out of it to feel the difference. Hold you hand up and look at your palm. Work it in and out of the light and see how it falls, what the intensity is. Try not to stand directly under the light, or in too hot a spot, so you are not washed out by the glare of the light.
While there are times you may want to be partially or fully in shadow for an effect, those times should be planned. Outside of an effect, be a good, light seeking, actor. You must be seen for the audience to watch your facial work.
J.T. Turner, The Actors Sensei