W
Watson A.Name - "Watt Sun
Guest
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@@
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@@