Re: LED brightness?

Peter Hucker wrote:
On Sat, 19 Nov 2005 18:46:17 -0000, John Fields <jfields@xxxxxxxxxxxxxxxxxxxxx> wrote:

On Sat, 19 Nov 2005 16:19:48 -0000, "Peter Hucker" <no@xxxxxxxx>
wrote:

On Sat, 19 Nov 2005 16:12:53 -0000, John Fields <jfields@xxxxxxxxxxxxxxxxxxxxx> 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.



I was trying to go by this:
http://en.wikipedia.org/wiki/Luminous_intensity
But there are too many different units!

So what you're saying is the way they quote them in catalogues (mcd) is total light output, whereas luminance (in mcd/sq.m) is what I was thinking of? 


---
Yes.



Thanks, just changed to buying a completely different set :-)

Why is there so much difference in specs with LEDs? Aren't they all basically the same technology?



That's a non sequitur. Tungsten filament incandescent lamps are
all basically the same technology, yet they come in many different
configurations. Same is true of LEDs, which come in various
colors, shapes, sizes, viewing angles, mcd ratings etc.
I suppose that manufacturers decide where they think there is,
or will be, a need, and make things with specs that meet the need.
That would result in the many different LEDs that are available.

Ed

.

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