LED light output?

J

Jeff

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I have an array of an unkown LED and a lightmeter that only reads
footcandles and is color and cosine corrected.
Is there a way to convert footcandles to mcd (roughly)?
LEDs are red, water clear and at ~6mA are quite bright.
Jeff
 
In article <0o0mb.12634$Ec1.1119801@bgtnsc05-
news.ops.worldnet.att.net>, frontline_electronics@NSatt.net
mentioned...
I have an array of an unkown LED and a lightmeter that only reads
footcandles and is color and cosine corrected.
Is there a way to convert footcandles to mcd (roughly)?
LEDs are red, water clear and at ~6mA are quite bright.
Jeff
You need to go read Don K's lighting web pages. You can also go to
his LED pages from there.

http://members.misty.com/don/light.html

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Jeff wrote:
I have an array of an unkown LED and a lightmeter that only reads
footcandles and is color and cosine corrected.
Is there a way to convert footcandles to mcd (roughly)?
LEDs are red, water clear and at ~6mA are quite bright.
Jeff
Hi,

0.0929 footcandles [fc] = 1 lux [lx] = 1 lumen per square meter
[lm/m^2]. On the other hand, 1 candela [cd] = 1 lumen/sterad [lm/sr].
So, in order to convert from lux to candela (or millicandela [mcd]) you
have to convert the illuminated area (measured in square meter) to the
corresponding solid angle (measured in sterad): to this end, divide the
illuminated area by the square of its distance from the light source.

Hope this helps,

Martin.


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Jeff wrote:

I have an array of an unkown LED and a lightmeter that only reads
footcandles and is color and cosine corrected.
Is there a way to convert footcandles to mcd (roughly)?
LEDs are red, water clear and at ~6mA are quite bright.
Jeff

Hi,

0.0929 footcandles [fc] = 1 lux [lx] = 1 lumen per square meter
[lm/m^2]. On the other hand, 1 candela [cd] = 1 lumen/sterad [lm/sr].
So, in order to convert from lux to candela (or millicandela [mcd]) you
have to convert the illuminated area (measured in square meter) to the
corresponding solid angle (measured in sterad): to this end, divide the
illuminated area by the square of its distance from the light source.

Hope this helps,

Martin.


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Hi.
Thanks, thats what I needed, a description in english of
the math involved with these standards I am not used to
at all.
So we came to the conclusion last night after posting
the question that there are too many varriables to deal
with without a known reference to acheive an accurate
rough approximation within 200mcd or less.
(we = a few friends + a few beers)
I will order a few higher output LEDs for future
reference and maybe some other parts to make a
more accurate measurement tool.
Thanks to all.
Jeff
 
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Jeff wrote:
Hi.
Thanks, thats what I needed, a description in english of
the math involved with these standards I am not used to
at all.
So we came to the conclusion last night after posting
the question that there are too many varriables to deal
with without a known reference to acheive an accurate
rough approximation within 200mcd or less.
(we = a few friends + a few beers)
I will order a few higher output LEDs for future
reference and maybe some other parts to make a
more accurate measurement tool.
Thanks to all.
Jeff

Hi,

assuming that you shine the light from a LED under test onto your
footcandlemeter from a distance d, I find this recipe from the relations
of my last post:

Multiply the meter reading in footcandles by 1.076*(d/cm)^2 to obtain
the LED rating in millicandela.

Example: a meter reading of 20 fc for a distance of 10 cm yields 2152
mcd.

If the LED is from a reputable manufacturer, the result should agree
with the datasheet specifications.

Martin.


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In article <0o0mb.12634$Ec1.1119801@bgtnsc05-news.ops.worldnet.att.net>,
Jeff wrote:
I have an array of an unkown LED and a lightmeter that only reads
footcandles and is color and cosine corrected.
Is there a way to convert footcandles to mcd (roughly)?
LEDs are red, water clear and at ~6mA are quite bright.
Given the above, mcd is 1,000 times the footcandles, multiplied by the
square of the distance in feet between the LED and the lightmeter.

Give or take various meter errors including any in its color correction,
as well as matching human vision in determining visibility of different
wavelengths of red, blue and violet.

- Don Klipstein (don@misty.com, http://www.misty.com/~don/ledx.html)
 
"Don Klipstein" <don@manx.misty.com> wrote in message
news:slrnbpmnr4.6ek.don@manx.misty.com...
In article <0o0mb.12634$Ec1.1119801@bgtnsc05-news.ops.worldnet.att.net>,
Jeff wrote:
I have an array of an unkown LED and a lightmeter that only reads
footcandles and is color and cosine corrected.
Is there a way to convert footcandles to mcd (roughly)?
LEDs are red, water clear and at ~6mA are quite bright.

Given the above, mcd is 1,000 times the footcandles, multiplied by the
square of the distance in feet between the LED and the lightmeter.

Give or take various meter errors including any in its color correction,
as well as matching human vision in determining visibility of different
wavelengths of red, blue and violet.

- Don Klipstein (don@misty.com, http://www.misty.com/~don/ledx.html)
Don and all thanks!
Don for the great site I have used several times and
will again I am sure.
Others for the referal and taking the time to respond,
I did need the discription of the math, we had figured
around 17 possiable varriables with an error factor for
each and without a reference.... impossiable.
I did not have a single LED that output over 80mcd
max and most were below that. (meter starts at 10ftC
with 3 scales going up)
These were more in the area of 1000mcd+ as of now
I still can not measure them. In another week I will be
able to within a few tens of mcd.
Jeff
 

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