Re: Ultra bright LEDs

From: Don Klipstein (don_at_manx.misty.com)
Date: 12/12/04 

Date: Sun, 12 Dec 2004 06:49:10 +0000 (UTC)

In article <xEIud.17538$d94.546885@phobos.telenet-ops.be>, CWatters wrote:
>I've been trying to assess the state of the art for white LEDs intended for
>illumination. The efficiency of production LEDs to top out around 20 Lumens
>per Watt with some press releases indicating that we can expect double or
>triple that in 2005 perhaps.
>
>So how come the net is full of sites that appear to have LED products
>producing far more Lumens/Watt?

  There have been efficiency claims for LEDs that ranged from (in my
words) "awfully optimistic" to dishonest for quite a few years now.

  One site with a name that appears intended to inspire the word "green"
as in pro-environment sold LED products in the mid or late 1990's and
claimed then that LEDs were the light sources that had ultimate
efficiency, greater than that of fluorescent and compact fluorescent
lamps.

  One little note:
  Some other people got taken in by some LED datasheets that had extreme
figures of luminous efficacy in terms of lumens per watt. What they did
not notice was that this was luminous efficacy of the emited light, which
was a figure for conversion between radiometric and photometric units - as
in this was a figure of lumens out per watt out (or millilumens out per
milliwatt out, or microlumens out per watt out), and not lumens out per
watt in. Even in the early 1980's I saw LED datasheets with green
(yellow-green) LEDs with "luminous efficacy" over 500 lumens per watt, but
that was lumens out per watt out and their "overall luminous efficacy" in
lumens out per watt in was more like 1.

 - Don Klipstein (don@misty.com)

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