[Laser] Standard LED question.

[KY1K]

Hi Kurt,

There are a few exceptions, but the vast majority of LED's are rated at 15 
to 20 ma.

The high 'mcd' ratings come from the reduced 'viewing angle' and the fact 
that there are differing processes that produce slightly improved efficiencies.

There is a fundamental problem with LED's and their packages. The die is 
surrounded by plastic, which doesn't dissipate heat well, which is the 
reason for the seemingly low power output of the LED. This is why most 
LED's can be pulsed at much higher currents.

Lately, some LED's have been put in packages with solder tabs, allowing 
them to dissipate more heat. These (and other packaging methods) do have 
slightly higher rated currents.

If it's mounted in a small package without a heat sink, the chances are 
very good that it's a 20 ma rating.

Bye the way, most of the higher intensity LED's are not expensive, even 
though the seller tries to make you think it is a really special LED:>:

There are some specialty LED's that have collimating lens built in, these 
can get you down to 2 or 3 degree divergences, which ain't too bad for our 
purposes.

GL.

Art




At 11:07 PM 4/14/2005, you wrote:
>Are all LEDs rated at a 20mA draw which is what I see in all the
>manufacturers specs?  I have three dozen 3,000mCd red LEDs but no specs.  If
>I run them off of 12V with about 1200 Ohm resistance, I get a current draw
>of 15mA and an input voltage of about 1.8V.  I can lower the resistance to
>increase current to 20mA and thus the brightness, but I'd rather run them on
>the safe side.
>
>What is the proper procedure for determining voltage\current of the average
>LED?
>
>Kurt
>
>Rosetta Proving Ground, Nevada
>Hell's Laboratory
>
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