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LED Measurements

T

TKM

Jan 1, 1970
0
What's the sense of this group regarding the current accuracy of LED
measurements? Are we seeing realistic numbers, especially lumen output,
from the manufacturers, test labs and others? What about the answers that
come from sites such as: http://led.linear1.org/lumen.wiz (millicandelas to
lumens) -- lots of caveats listed and it sounds like there's a major problem
defining LED beam angle.

I know there is standards development work going on that will likely help,
but has anyone done testing such as taking intensity data, doing a lumen
calculation and then putting the LED in an integrating sphere?

Terry McGowan
 
V

Victor Roberts

Jan 1, 1970
0
What's the sense of this group regarding the current accuracy of LED
measurements? Are we seeing realistic numbers, especially lumen output,
from the manufacturers, test labs and others? What about the answers that
come from sites such as: http://led.linear1.org/lumen.wiz (millicandelas to
lumens) -- lots of caveats listed and it sounds like there's a major problem
defining LED beam angle.

You've already identified the problem with lumen.wiz. Lumen
Wiz states that it assumes the intensity values are average
across the beam while most, or even all, manufacturers give
peak intensity at the center of the beam. There is no
reliable way to convert a single intensity value into flux.
If you have the brightness distribution curve, then you can
integrate all that data. Good manufacturers give flux in
lumens.
I know there is standards development work going on that will likely help,
but has anyone done testing such as taking intensity data, doing a lumen
calculation and then putting the LED in an integrating sphere?

I haven't, but folks from Labsphere hang out here and they
have a nice small sphere designed for measuring LEDs. In
fact, someone, I think Labsphere, introduced a
battery-powered, hand-held, LED-size sphere with all the
electronics in the handle perhaps 2 years ago. Just the
thing to carry around at Light Fair or an LED meetings to
test devices on display. I little real data would go a long
way right now.


--
Vic Roberts
http://www.RobertsResearchInc.com
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C

Clive Mitchell

Jan 1, 1970
0
Victor Roberts said:
I haven't, but folks from Labsphere hang out here and they have a nice
small sphere designed for measuring LEDs. In fact, someone, I think
Labsphere, introduced a battery-powered, hand-held, LED-size sphere
with all the electronics in the handle perhaps 2 years ago. Just the
thing to carry around at Light Fair or an LED meetings to test devices
on display. I little real data would go a long way right now.

We'll have to get one of those for PLASA next year Adam. :)
 
C

Clive Mitchell

Jan 1, 1970
0
Adam said:
Think Santa would have to be feeling especially generous, fun you could
have watching exhibitors turn pale and mumble about typical outputs
would be almost worth it.

The cheaper option might be to glue a ping pong ball on a stick and
attach it to a multimeter with a bit of coiled telephone lead. Then
just walk about pointing it at their displays, looking at the meter and
then drawing your breath in sharply while shaking your head. Just like
we were walking around feeling the temperature of the sources and...
and... well basically burning our hands. :)

I mean, it's a foregone conclusion that they've probably hyped the
intensities a bit. We could have a batch of "INTENSITY EXAGGERATED"
stickers to put on their products.
 
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