What’s cool about light is that, in linear space, it literally just adds together. I’ve known this in 3D for a while, but it’s quite different to try it out in the real world. Here’s two pics from my bathroom. The first: with 3 light bulbs on, plus my cell phone light and a flash light. The second: each of those lights shot individually, and all the photos set to linear dodge in Photoshop. Except for tiny errors (camera wiggle, me getting in the shot) they produce identical images.
Science! 
The Og Bog Blog 