> Another concern about luxeon power leds:
>
> Why does the typical lumens value given at [W] unit rather than [lm] unit
> for royal blue leds?
>
> The datasheets note that "Royal Blue product is binned by radiometric
> power
> and peak wavelength rather than photometric lumens and dominant
> wavelength."
> (the state has been given but no description.)
>
> Also i read an article named "More Light - Practical high-power LEDs" from
> Elektor Magazine. There says: "The royal blue version emits light with a
> wavelength of 450nm and the eye is so insensitive to this colour that the
> luminous flux is given in miliwatts. This parameter gives some indication
> of
> the LED efficiency; 10% of the 1W of electrical power is converted to
> visible light."
>
> What is the real explanation of this case?


As I recall, Lumens refer to an apparent brightness to a human observer.
The watts per square meter "power density" at various wavelengths is run
through a photopic filter to attenuate wavelengths the eye responds poorly
to so the lumen value approximates what an observer would say the
brightness of the lamp is. I wrote some PIC code to do this, taking values
from a spectrometer, multiplying by the photopic filter values for that
wavelength, then adding the results.

The power output (in watts) ignores the brightness as preceived by the eye
and, instead, just considers all power equally. The royal blue LED is
often used for purposes other than "lighting" (where someone looks at the
light). I used it in a dental curing light where the light activates
curing components of the composite. The light characteristic we're
interested in this application is watts per square meter (they use
milliwatts per square centimeter, but I think metric should use the basic
units with just a single scaling prefix!) at the appropriate wavelength.

Harold



-- 
FCC Rules Updated Daily at http://www.hallikainen.com
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist