[geeks] LED home lighting project

[Phil Stracchino]

Charles Shannon Hendrix wrote:
> For some time I've been wanting to build some light systems for various
> areas at home, using LEDs.
> 
> For example, lighting the front of things like A/V equipment, computer
> equipment, closets, and various places like that.
> 
> The traditional home lighting stuff is too bulky, and I don't like
> things like the "light strings".
> 
> The only things I have found small enough and bright enough, have been
> things like automotive spot lamps for clipping in the car, or various
> light decorations for computers.
> 
> The automotive stuff is battery powered, and I'd hate to buy a bunch and
> cut them up to run DC wiring.
> 
> The computer stuff is usually overpriced, or not quite the right thing
> for lighting an area or piece of equipment.
> 
> I also would like to keep the lights hidden, or at least small.
> 
> I've done some experiments which were OK, so now I'm looking to do
> something more permanent.
> 
> Ideas or sources appreciated.

I believe you can obtain white LEDs from Radio Shack; I'm not sure
whether you can buy them in bulk there yet.  You certainly ought to be
able to find places where you can.  Other colors will of course be
easier.  You can power the thing from, for instance, a wall-wart, a
laptop power adapter, or just about any other low-voltage DC power
supply.  Anywhere in the 3v to 5v range is probably fine; read the specs
on the device.  Wire your LEDs in parallel to a common bus; put a
current-limiting resistor in series with each LED.  Given the nominal
current rating of the device, you should be able to trivially calculate
the required resistance using good old V=IR.  If in doubt, or if there
is not a cheaply and commonly available resistor yielding the current
you want, err on the high side of resistance rather than the low; if
memory serves correctly, service lifetime of an LED varies as the
inverse fourth power of the driving current.  10% tolerance resistors
are quite sufficient.

When I used this method to build a high-level brake light for my car, I
tried two packaging approaches.
The first was to cast the entire array (50 10mm high-output red LEDs)
into an acrylic-resin bar poured in place in a mold I made from ....  uh
.... OK, I don't remember what I made the mold from.  It might have been
ABS sheet.  However, for a light bar something like thirty-five inches
long and only about five eighths of an inch thick, this proved
excessively brittle.  For small light modules such as you're likely to
be building, it would probably work just fine.
My second attempt, fabricated from heat-formed 1/8" Plexiglass, was much
more successful, but probably too elaborate for what you want to do.  If
you were to compromise and insert the LEDs into holes drilled in a
Plexiglass block and potted in place with clear acrylic resin, you could
probably make the block serve both as mounting and as light-pipe.


-- 
 Phil Stracchino
 Renaissance Man, Unix generalist, Perl hacker
 phil.stracchino at speakeasy.net
 phil.stracchino at ceva-dsp.com
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