I don't know the answer to your question, specifically. But it might be helpful to know that the power/strength of light diminishes according to the inverse-sq

I don't know the answer to your question, specifically. But it might be helpful to know that the power/strength of light diminishes according to the inverse-square law. That is, if one doubles the distance, there is quarter the amount of light falling on a given area (vis: it is quarter of the strength), and, vice versa, if one halves the distance, the amount of light increases four-fold. Due to this rate of fall-off, it means that it is much more effective if the light source is closer.