[astfgl]

A local pine furniture place makes things like this to order, and does a really good job. It's actually two double-door units bolted together, I havn't finished wiring the left hand side yet.

EDIT: Forgot to say, when LEDs are in series, the current draw is just as if there were one LED in the circuit, but the voltage supply must be the sum of each LED's voltage drop, plus a little bit. When in parallel, the current is the sum of each LED's current and the voltage supply must be larger than the LED with the highest voltage drop. That should make the rest of the post easier to understand. Remember, LEDs are semiconductors and do not behave in a strictly linear fashion like resistors, capacitors, and inductors.

On topic, I've scavenged power from my answering maching plugpack, which delivers 15V. Each LED drops about 3V, so with 4 LEDs in series I have 15V-4x3V=3V overhead. The appropriate resistor is 3V/15mA=200ohms. I used a 500 variable resistor(potentiometer) and tweaked the final value whilst looking at a current meter, as there are manufacturing variations in both LED current draw and resistor resistance.

If I had a 12V or 9V supply, I would have used two sets of two leds in parallel, which would have doubled the current draw. When selecting LEDs, look for the "forward voltage drop", of Vf. This is the minimum voltage for the LED to illuminate. Below this, the LED is dark or glowing so dimly it's useless as a light source. Once you have this minimum, you must add a resistor in series with the LED(or LEDs) to limit the current to(or below) it's rated current.

The rated current on a LED is usually a MAXIMUM and much above that the color will (briefly) change as the semiconductor junction overheats, increasing resistance in a runaway condition, to the point where the epoxy/acrylic/plastic housing in contact with the chip vaporises and there is a *crack*, or if you're really lucky, a *pop* and shrapnel.

As to brightness, 500mCd is bright to look at, and will leave a "spot" in your vision after a few seconds which lasts less than a minute. 10,000mCd is very unpleasant to look at and will leave several spots and streaks in your vision which persist after several minutes. I plan to avoid repeating that experience in the future. ;-) Also, the lens shape is critical. 10,000mCd would be great for lighting, but mine have a beam spread of 25 degrees. Great for spot illumination, bad for area. The 180 degree LEDS look longer to find and cost 50c each, but are well worth it and more than bright enough. I'll be adding a dimmer potentiometer to the common supply when it's done, as it lights up the room at night.