[montecarl]

Exponential growth is awesome! However, I was curious about the maximum theoretical lumens per watt to determine when the growth will fall flat. A current LED bulb gives about 60 lumens per watt. While an ideal monochromatic light source could give 683.[1] So it looks like there is _only_ one order of magnitude left in efficiency gains.

1: http://en.wikipedia.org/wiki/Luminous_efficacy

[jzwinck]

That 683 lumens per watt number is, as you say, for a monochromatic light. This is not useful for humans to see with[1]; the actual limit for human vision is about 300 lumens per watt[2]. That's an upper bound even ignoring losses, and some LEDs are around 70 now, so the remaining efficiency gains we can make seem limited to about 3x.

[1] http://www.cool.conservation-us.org/byorg/us-doe/color_quali...

[2] http://phys.org/news202453100.html