125 mW of 555 looks (appearance) by eye to be same as 1W of 473nm
~1/8th
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from threads at candlepowerforums
According to wikipedia, ideal 555nm light will give 683lm/W.
1 watt of 555 nm green light equals 683 lumens.
another writes ...
By definition, at the peak sensitivity of the eye (green 555nm) 1 Watt equals 680 lumens.
and from CPF
A 532nm laser has a luminosity function of .89, and the other, "dimmer" colors have their respective luminosity functions.
What does this mean?
For example, 100mW of pure 532nm light will have (683lm/W)(0.1W)(.89)=61 lumens. That's the same brightness of a Surefire E2e flashlight! And I thought that lasers were dim.
A 200mW 635nm laser will only put out (683lm/W)(0.2W)(.24)=33 lumens, or appear half as bright as a green laser of half the power output. 473nm blue is even dimmer, and the near-IR 670nm red is very very dim.
pseudonomen137 pseudonomen137 is offline
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Default Re: Luminosity of lasers (math)
Be careful about some of those generalizations. Lumens can figure total power of a specific wavelength, but candelas (lumens/steradian) take area into account too, which really changes things when you consider collimation.
Lumens are not a measure of brightness and you will want to be careful not to get the two confused (in fact, with lasers, the term 'brightness' takes on a completely different meaning scientifically). 2x lumens will not correspond to 2x visual brightness, and you have to be careful as to what you are considering to be "bright". Lumens will tell you the total visual brightness the beam can project, given a set area, but because of different spot sizes and such, it will not give you an accurate indication of how bright the dot is.
Honestly.. lumens just aren't a unit that is very compatible with lasers, though I guess this is useful to know nonetheless
("Hey, this kW CO2 laser is only 0 lumens... it can't be TOO dangerous" )
((((((((((((((((reply to above post
You're right, my original post should have replaced any instance of "brightness" with "apparent light output".
If we want to figure candela, then it seems that a 100mW 532nm laser with a divergence of 1mrad puts out 80 million candlepower.
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FNinjaP90 FNinjaP90 is offline
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Default Re: Luminosity of lasers (math)
Looking at the equations I pulled up from Wikipedia,
The steradian(a unit of solid angle) is analgous to a jousting lance or laser beam(lower solid angle) compared to an ice cream cone or flashlight beam(higher solid angle).
Candela = 683(luminosity function)(W/sr)
Lumen=(Candela)(sr)
The steradians cancel out, and all you're left with is Lumen=683(luminosity function)(W).
Am I right? Anyway, it's perfectly possible to calculate the laser beam's solid angle, assuming that the beam has an initial diameter of 0 and spreads out into space as a cone. The arclength of 1 steradian is 65.53deg. Figure 1mrad as the arclength(divergence) of the laser beam, convert that to degrees, divide it by 65.53deg, and square the figure to find the ratio of the laser beam solid angle to the solid angle of 1 steradian.
Still, the solid angle(steradian) should cancel out in calculating lumens, which is logical since a laser with a large divergence illuminates an unlit room just as well as a laser with very small divergence. The same as how the Surefire turbohead has a tighter focus than a regular head, yet they both give the same lumen output with the same bulb. Candlepower(candela) increases as a beam is more tightly focused, but luminosity disregards focus and is only dependent on the total light output of the light source.
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I cannot say all the above is accurate
