Say I have one LED in a flashlight, it produces some light.
Now, if I have 3 of those LEDs in the same flashlight, each LED receiving the same amount of energy than the single LED was receiving in the model described above (thus producing, individually, the same amount of light), will I get (perceive) more light? Will it be brighter? (considering the 3 LEDs very close to each other, same direction, etc.)
Quickly said: does the perceived light "sum up"?