Attila Muhi writes:

> I need a monochrome (almost) light source for a project. So far I
> have been playing with high intensity LED:s around 650 nm
> (EL383-2SDRC), with an output of about 3700 mcd at 20mA.  For some
> reasons I need more light than that, so I run the LED:s at
> 50mA. This is way out of specs, which says a max fwd current of
> 35-40mA. I also need to run the current continously. I get a temp
> rise of course, the surface of the LED goes up to 42-43 degrees. The
> temp rise itself is no problem, but I wonder how much the
> overpowering affects the LED:s lifetime ?
>
> As far  as I can see, I have three alternatives:
> 
> Continue as before 
> Finding a better LED (Any ideas ?)
> Use a laser.  (expensive solution)

What about just running multiple LEDs?  LEDs are generally most
efficient at their rated current capacity (20 mA in most cases) so
you'll get more light from 40 mA through 2 LEDs (20 mA + 20 mA) than
from one.  (I presume packaging and/or alignment are issues preventing
multiple LEDs?)

Do you need a wide or narrow beam angle?  The mcd rating for LEDs is
taken at a small spot in the center.  The same LED (semiconductor)
could have a rating of anywhere between 1000 and 10,000 mcd based
entirely on the focus of the optics.

There are some absurdly bright LEDs on the market now, so if cost and
power requirements are of no concern, you *should* be able to find a
simgle LED solution.

-p.
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