Re: LED brightness?

On Tue, 29 Nov 2005 00:03:43 -0000, Don Klipstein <don@xxxxxxxxxxxxxx> wrote:

In article <1ljun19ho2m9a60vbg1m55hv7t2vfj5kt5@xxxxxxx>, John Fields wrote: 
On Sat, 19 Nov 2005 15:02:01 -0000, "Peter Hucker" <no@xxxxxxxx>
wrote:

I'm wanting to purchase bright LEDs, but am confused by the specs.

Am I correct in the following assumption?

A 100mcd LED with a viewing angle of 30 degrees will light the surface
in front of it at the same brightness as a 100mcd LED with a viewing
angle of 15 degrees, but will light a larger area, therefore is giving
off more light in total.


---
No.

100 millicandelas is the total light output, so the area illuminated
by the LED with the larger beamwidth will be dimmer.


  Candela is not a unit of total light output, but of "beam candlepower".
1 candela illuminates a spot on a surface 1 meter away to the extent of 1
lux.

  The units of total light output are "spherical candlepower" (candela
averaged over all directions, including directions into which no light is
sent), and the lumen.  1 lumen is the total light in a "solid angle" of 1
steradian (1/4-pi hemisphere) where the light has an intensity uniformly
of 1 candela.  A "spherical candlepower" is 4-pi lumens, the output of a 1
candela omnidirectional source.

- Don Klipstein (don@xxxxxxxxx) 

I purchased a range of LEDs and tested them.  The mcd rating appears to be TOTAL light output.

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