Way to Measure 5000 mCd White LEDs?

[Watson A.Name - Watt Sun]

I bought a hundred 3 mm white LEDs from a company in Hong Kong that
auctioned them on Ebay, for about a quarter apiece. I got them by
registered mail today, and put a few on a power supply to see how they
lit up. I put 25 mA thru them, and they don't seem to be anywhere
near the advertised 5000 mCd.

I have built a simple comparison test into a cardboard box. I cut a
hole in one end for the LED, and to the other end I taped a
photovoltaic cell that's about 2 inches square. I can put a lit LED
thru the hole and measure the output current of the photocell with my
DMM and get a few dozen microamps depending on the LED. But I have no
way of calibrating this to a known value of mCd. The box is about 7
inches long, so the distance between the LED and cell is about 6 or 7
inches.

Any idea how I can make a system that givse a mCd value? I know about
the grease spot method of comparing two light sources. Thanks.

--
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Don't be ripped off by the big book dealers. Go to the URL
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http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Steve J. Noll]

I have a calibrated Tek J17 & J1805.
Could measure some for you if you're located in the US.

I bought a hundred 3 mm white LEDs from a company in Hong Kong that
auctioned them on Ebay, for about a quarter apiece. I got them by
registered mail today, and put a few on a power supply to see how they
lit up. I put 25 mA thru them, and they don't seem to be anywhere
near the advertised 5000 mCd.

I have built a simple comparison test into a cardboard box. I cut a
hole in one end for the LED, and to the other end I taped a
photovoltaic cell that's about 2 inches square. I can put a lit LED
thru the hole and measure the output current of the photocell with my
DMM and get a few dozen microamps depending on the LED. But I have no
way of calibrating this to a known value of mCd. The box is about 7
inches long, so the distance between the LED and cell is about 6 or 7
inches.

Any idea how I can make a system that givse a mCd value? I know about
the grease spot method of comparing two light sources. Thanks.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

Steve J. Noll | Ventura California |
| The Used High-Tech Equipment Dealer Directory
| http://www.big-list.com
| The Peltier Device Information Site:
| http://www.peltier-info.com

 

[Watson A.Name - Watt Sun]

I have a calibrated Tek J17 & J1805.
Could measure some for you if you're located in the US.

Yeah, I'm sending some off to another guy for measurement. Problem is
that I'm still dependent on others for this, so I'd like to
'calibrate' something, or buy a calibrated something. Like, I can
light a candle and say, gee, here's one candlepower! Wow! Hi-tech!
But I'd like something a bit more accurate. And not a fire hazard.

I'm also in So. Calif, a few miles from Dizzyland, where the train
falls off the tracks. ;-P

Steve J. Noll | Ventura California |
| The Used High-Tech Equipment Dealer Directory
| http://www.big-list.com
| The Peltier Device Information Site:
| http://www.peltier-info.com

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[[email protected]]

Yeah, I'm sending some off to another guy for measurement. Problem is
that I'm still dependent on others for this, so I'd like to
'calibrate' something, or buy a calibrated something. Like, I can
light a candle and say, gee, here's one candlepower! Wow! Hi-tech!
But I'd like something a bit more accurate. And not a fire hazard.

I'm also in So. Calif, a few miles from Dizzyland, where the train
falls off the tracks. ;-P

You could use the tested LED's as standards, put them in
your box and see how many ua you get per mCd, and derive an
instrument that way.

 

[Watson A.Name - Watt Sun]

You could use the tested LED's as standards, put them in
your box and see how many ua you get per mCd, and derive an
instrument that way.

I hadn't planned on asking that the LEDs be returned. All I would ask
for is an average mCd for a dozen or so.

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[William P.N. Smith]

[email protected] mentioned...

I hadn't planned on asking that the LEDs be returned. All I would ask
for is an average mCd for a dozen or so.

So test the ahead of time and record the numbers, then compare to the
numbers you get with the unknown ones.

 

[Watson A.Name - Watt Sun]

So test the ahead of time and record the numbers, then compare to the
numbers you get with the unknown ones.

Each LED would have to be labeled and accounted for. Too much hassle
for the other guy doing the testing.

Then I have to correct for changing conditions on my end. It would be
much easier to do things with the reference as a direct comparison.
That way, I could put the unknowwn and reference LEDs in series so
that the current is exactly the same, with no deviations caused by
measurement errors. Thanks for the idea, tho.


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@