Gerhard points out and I'd like to make more clear that each LED
produces a miniscule amount of light compared to a 100W bulb.

The LED consumes 20mA at 2.5V (approx.)  Therefore it consumes 50mW of
power per LED.  The lightbulb consumes 100W of power per bulb.  The
LED is more efficient - let's assume it's as efficient as a compact
flourescent bulb, which is about 4 times more efficient.  Therefore
you need to consume 25W of power with your LED array in order to come
close to a 100W light bulb.

25W at 50mW per LED comes to 500 LEDs.

So take ten of your panels, and you should get close to the brightness
of an average 100W light bulb.

You can do a more rigourous examination by researching the difference
between lumens and candela, and figuring out the physical and
mathematical conversion between the two.  LEDs, being directional, are
rated in candela, while light bulbs are measured in lumens.  Then
you'll be able to determine the number of LEDs you need given the
ratings of the particular LED you are using.  If you are using very
cheap white LEDs then you'll need thousands instead of hundreds.

Of course, it isn't that simple either, since the rating of the LED is
usually at maximum power, and most high power white LEDs only run at
maximum for 1000 hours before decreasing in brightness significantly
or failing.  Heatsinking them properly is non-trivial for running at
max rating.

Then you need to determine how to power and array them, since one
failed LED could dim or blank out a string of them in your array. 
Improper powering could lead to one bad LED damaging others, the power
supply, or the whole unit.

etc, etc, etc.

So at this point it's not cost effective on the majority of metrics to
use LEDs in place of flourescents and incandescent bulbs for general
area lighting.  Certain applications shine with LEDs, though.  Car
taillights need to be rugged, and turn on instantly which LEDs excel
at.  Spotlights are directional and LEDs are directional - an example
would be traffic lights.  They are very directional, and since single
colors can be used they are very cheaply made as LED product.  Further
the instant turn on time is again good for this application. 
Flshlights are directional, need to be rugged, and have to be low
power, so even expensive high output white LEDs can be a very good
match there.

-Adam

On 2/27/06, Jason <pic@canadaspeaks.com> wrote:
> For a project I'm working on, I had to build a panel of 50 superbright LEDs
> on a 2.5x3.5" panel.  I thought that while I had it, I could do some
> experimenting with LED lighting.
>
> I find the results very disappointing.  I have a flashlight with a single 1
> watt luxeon LED that looks at least 10 times brighter than my panel when I
> shine them on the wall (and the flashlight is spread out more).
>
> I'm running the LEDs at 20mA each, and each one has it's normal 'blinding'
> brightness when I look at it head on.  It seems like it will take thousands
> and more power than an incandescent bulb to light the room.
>
> Is there some trick to using LEDs as area lighting or are normal 5mm LEDs
> just not suitable?
>
>
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