Letter Re: Low Power D.C. Lighting

James Wesley;
Vlad wrote at the end of his piece, “Wish I had a better closing line but it is getting late and I need to go dig up a potentiometer for this lamp.”  Unfortunately, that isn’t going to do a lot of good.  Because an LED is a diode (the D in LED) it is pretty much on or off.  Dimmable LEDs are usually dimmed via Pulse-width Modulation — essentially, turning the LED on and off very quickly.  This doesn’t harm the LED, but it needs a particular circuit to do it.  Reducing the voltage will dim it — but it will happen with such a quick drop off that the “sweet spot” you are looking for will be minisculely tiny and not something you are going to hit without a very sensitive pot and a steady hand.  Several web sites detail how to make a PWM dimmer with the ubiquitous 555 timer chip (The piece at Instructables on this topic  is good).  That would be the best way to dim the LEDs themselves.

Since LEDs draw so little current, I do my “dimming” in stages by either switching in a different number of LEDs for different levels.  PWM isn’t hard with a timer chip, but PWM isn’t hardened at all against EMP (since a timer chip is an IC) and introduces more points of failure.

Also, on rigging for red — remember that the opposite is also true.  When you want to get the most vision for the least number of LEDs, go to the other end of the spectrum and get one of the blue LEDs.  I end up putting something over most of the blue LEDs that manufacturers love putting on electronics now, because a single one of them is more than enough to be a nightlight, and having just a few of them going at once will light a room up brighter than a full moon.  Because they also produce virtually no heat, you can put them virtually anywhere without a fire risk, including boxing them up with only a slit or pinhole to control the light output. – Phelps