P3D Re: White LED efficiency.

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>Is this optical Lumens out per electrical watt in or optical lumens out
>per optical watt out?

  I would assume it's for electrical watts.

  This caving LED light page:
http://www.hdssystems.com/NSSLEDArticle.htm

  has an article about LED lighting.

---quote---
So let's talk about the efficiency of these LEDs.
The white LEDs have advanced to the point where
they are now more efficient than the low power
(less than 2 watt) incandescent light bulbs.
They are just about as efficient as the higher
power bulbs (3 to 5 watts) incandescent light bulbs.
Within another year they will have passed the higher
power bulbs in efficiency.
---end---

  The article date is June 99 so I guess
it is still true.


>I don't think so. Think about a cube around the bulb. The condenser can
>usually collect light from much of one face. A good afocal reflector
>could reverse the light from the opposite face. But nobody uses these.
>They use a simple spherical mirror which is too close to the filament.
>As a result, much of the reflected light misses the collection optics.
>Some of the light hits the filament itself and never makes it through to
>the collection optics. The mirror is usually less than 85% reflective.
>All together I figure you are lucky if you can capture and control 20%.
>I have no references for this but simple geometric optics is where I
>come up with this.

  I think projector bulbs are the exception. They have
the filiament wound in flat coils so that the reflector
images the coil back to fill in the gaps between the
coils. Thus you have a flat emitting surface which will
put most of the light towards the condensor or back to
the reflector.

  So with projector bulbs I believe you would get
more than 20% of the light to the film. THough I
don't have numbers to prove this. Perhaps BobH could
help there.

  With the bulbs that are usually used in viewers
I would guess that you are correct about the 20%.

Greg E.