Re: luminous efficiency (was Re: Season misconceptions in newspaper)

["Carl E. Mungan" <mungan@USNA.EDU>]

> What surprised me is that 60W halogen bulbs have comparable rated light
> output to 60W regular bulbs the last time I looked at them in the store.
> They usually have some claims about being "more efficient".  Perhaps
> they put out more light in the more visible portion of the spectrum to
> validate the claim of higher efficiency?

electric power consumption = 60 W
optical power in the visible = lumens (lm) - this is marked on the package

Hence luminous efficiency = lm/W - typically 17 lm/W for incandescents and
100 lm/W for fluorescents - these are the benchmarks you want to compare
your bulb to for claims of efficiency.

As suggested by BC, you can use a camera meter to estimate efficiency.
Better yet, you can measure the emission spectrum using a monochromator, and
use the standard CIE photopic (daylight eye responsivity) curve and 683 lm/W
conversion at its peak of 555 nm to calculate it. (Yes, this means the
largest possible efficiency a source could have is 683 lm/W and it would be
green, probably an LED of the future.) One should either use an integrating
sphere or assumed (probably isotropic) angular emission pattern.

additional references:
* http://usna.edu/Users/physics/mungan/Scholarship/LightOutput.pdf
* TPT article by MacIsaac
* PHYS-L archives