Calculated from the light - and dark-forward curve, usually gives you values that are slightly too low because the diode curves from the light and dark measurements are slightly different.

When he left the room, it was like the end of a movie, when the lights come back on, and you look around, and then remember where you were and what you were doing.

Or if the baby has just been crying, and their eyes are red, we might lighten the eyes.