Luminous efficacy converter
Convert lumens per watt into the percentage of perfect it represents, and into the watts a given light output would cost.
That's 1.67× as efficient as a fluorescent tube, while a modern LED is 1.2× better. An 800 lumen bulb at that efficiency would draw about 8 watts.
What it means
How efficient is that?
The 683 lm/W ceiling is for pure 555 nm green light. Any usable white light must spread across the spectrum, so about 250–350 lm/W is the practical limit.
Every unit
Your efficacy in every unit
Learn
Three things worth knowing
-
800 lumens is the old 60 W bulb
At 14 lm/W that took 57 watts. At 120 lm/W an LED does it in under 7. The lumens are what you buy; the watts are what you pay for.
-
The lumen is an eye measurement
It is weighted by the standard human response curve, which peaks in the green. That is why efficacy has a hard ceiling at all: the unit is defined from that curve.
-
Watts are not brightness
A 10 W LED and a 60 W filament bulb give the same light. Buying by wattage made sense only while every bulb had the same efficacy.
Shortcuts
Popular efficacy conversions
Background
About luminous efficacy
Luminous efficacy is how many lumens of visible light a lamp gets out of each watt it draws. A filament bulb manages about 14; a modern LED reaches 120 or more.
The absolute ceiling is 683 lm/W, the efficacy of monochromatic green at 555 nm, where the eye is most sensitive. Nothing can beat it, because that is how the lumen is defined.