I have been working on more lighting to use with my 12vdc system. up until now I have been using the 12v lights that came with my 2 sets of Harbor Freight solar panels. They lasted more than a year used almost every night. The tubes started turning black, but I think they quit because of a burned up resistor on the circuit board.
In the beginning I started replacing the HF lights with the 12 volt DC lights that you can get at WalMart-HomeDepot-Lowes for about $10. These lights can be found near the area with the fluorescent replacement bulbs and come in 6v and 12v versions. They run on batteries, the package says that it has a jack for external power but I couldn't find one. So I hacksawed an opening in the bottom of the fixture and soldered wires directly to the battery terminals. They put out about the same color and brightness as a HF bulb plus you can replace the bulb with a warmer color for about $7.
The old burned out HF bulbs were not really repairable but I realized that they make a perfect fixture to build LED lights out of. I also realized that I had all the parts onhand to build 2 of them rightaway. They are made with white 3v LEDs in strings of 3 with a 1 ohm leveling resister on each string. I am also using red LEDs in these lights to keep the light from looking too blue, these strings are 4 red 2v LEDs with a 2 ohm leveling resister. All the strings are paralleled and fed through an LM317t being used as a current regulator as described in this link...
http://www.reuk.co.uk/Using-The-LM317T-With-LED-Lighting.htm
The first LED light I made is 9 strings of white and 2 strings of red LEDs. This makes 27 white and 8 red. I have the Current regulator set to 220 milliamps cause, 11 LED strings times 20 milliamps equals 220ma. All the white LEDs are mounted on perfboard with hole-spacing perfect for an LED. The red LEDs have the clear round caps cut off to make them a wider beam and they are taped with red tape to the exterior if the fixture. This light works great and the LM317t with small heatsink was hardly getting warm to the touch. I tried to bend the LEDs outward on the perfboard to help to spread out the light but I had mounted the LEDs to close and I wasn't very successful.
After experimenting on the first light I made the second light with as many LEDs that would fit. It is 13 strings of white and 2 strings of red LEDs. This makes 39 white and 8 red. The current regulator is set to 300 milliamps since, 15 LED strings times 20 milliamps equals 300ma. The red LEDs are mounted on the perfboard along with the white ones. This light works a bit hotter though. With the higher current, the LM317t with small heatsink was running rather warm, almost hot to the touch. I was careful not to mount the LEDs down so close this time and was able to bend the LEDs outward so the light would cover a wider area.
The clear covers for the HF lights have some diffusion built into them but not enough at the bottom to spread out the beams coming from the LEDs. I cut out some circles from some clear perforated Freezer Bags and put them into the bottom of the covers and it smoothed out the beams really well. I also drilled some holes in the clear covers to help them get some air for cooling. Here is a picture of my computer area lit up by my LED lights. There is a light from a scanner that is out-of-sight at the top of the computer desk under the lip. You can see what nice color I get with some red LEDs in the mix.
These lights were easy to make but tedious and time consuming. The bigger light has 47 LEDs and 15 resisters, each with 2 leads, so there are over 100 solder connections on he backside of that perfboard. It took about 5 hours to build each light. I am very happy with the results, they will start at 11.8 volts and should be able to work all the way up to 40 volts. The addition of the red LEDs really improves the quality of the color and it's not a harsh blue anymore. one of them runs at about 3 watts and the other one runs at 4 watts.
W o o f -={(
