Letter Re: Lower Power DC Lighting

James Wesley:
I am writing by the light of a post-apocalyptic reading lamp I just constructed. From a string of LED Christmas lights, I removed two sections of just three LEDs each. To each of these I attached in series a single 100 Ohm resistor from the parts bin at Radio Shack. A goose-neck work light provided a good reflector and glare control. I cut the plug off the other end and crimped on the connectors appropriate to my battery. The battery was salvaged from a defunct computer UPS. They are common to alarm systems and are not expensive new. About 12″ of electrical tape to cover my splices and some string to arrange the bulbs just so in the work light. For a more permanent project I would solder and heat-shrink the splices and add a fuse.

In addition to looking like something just a bit too civilized to make it into a Mad Max movie this lamp puts out enough light to read by easily or do fairly detailed hand work. This is far more than my oil lamps can do. It draws .055 amp at 12 volts or seven tenths of a watt. Add a few bits of solar panel from some garden lights and the right diode and it can be made rechargeable. Tie it in to a more sophisticated off-grid power system for even better results.

I have small ones around and fear fire. Glass oil lamps are a nightmare. Even kept high and out of the way I can picture a high spirited little darling tossing an object just right and chaos follows.

If I can figure out how to integrate it aesthetically I plan to ‘nightlight’ the whole house. The same series circuit can be reproduced over and over in a parallel run using a light gauge wire.

Any parent can probably sympathize with trip hazards due to small people around. Stumbling around in the dark is dangerous and inefficient. Integrating something like this in a discreet way could be valuable. Maybe add a light sensor so they come on dimly as path lighting all night, and include an override switch to turn them up to full brightness as needed, or cut them entirely for light discipline. A relay powered by the solar panel could hold the circuit open until it had no more energy to contribute, then the lights would come on.

The same approach could be managed with unmodified Christmas lights and an inverter. Running an entire string of 60 lights plus the paying for losses in converting from AC to DC is fine of you have power to spare. But it silly when all you need is half a dozen lights at the right place.

Wish I had a better closing line but it is getting late and I need to go dig up a potentiometer for this lamp. – Vlad

JWR Replies: Low power DC lighting is great for retreats with alternative energy systems. And of course LEDs are the most energy-efficient source of light. For use at retreats, I recommend getting segmented strings of red LED lights. Several vendors make LED “Rope” strings divisible into three-foot segments that are custom made to work on 12 VDC power sources with no modification. (This is a plus for those that are not adept at wielding a soldering iron.) Why red, you ask? For preserving your best natural night vision. This is the same reason that many navies around the world still “rig for red”.