We've had snow on the ground since the day after Christmas, and I'm getting a little bit of cabin fever. We're also getting exciting about the upcoming gardening season, and Daya started sprouting vegetables inside. When she started searching for indoor grow lamps online, I was disgusted by the prices. So, I walked into my workshop to see if I had any LEDs laying around.
And that's when I remembered that I had LED strip.
I bought 3 meters of this at a great price while I was in India a year and a half ago. I thought I'd use it to bling-out my bike, but never got around to it. On later thought, glowing bikes are tacky. The grow lamp is a better use.
Each white rectangle is three LEDs: red, green and blue. The black rectangles are SMT resistors, 150 Ohm for the red and green channels, 330 Ohm for the blue channel. Each channel can be controlled independently to produce any color. The strip is printed on flexible circuit board with an adhesive backing. The strip can be cut at 3-LED increments. This stuff is pretty damn cool, and very easy to use in nearly anything.
I put the strips onto a piece of scrap wood grid that I found in the dumpster. I wired them together, and use an old laptop power supply to power them. Wiring requires a little bit of thought. A contiguous length of strip puts all of the LEDs in parallel. It's tempting to wire connect this directly to the power supply. However, the voltage drop of the lights is only about 0.7V. Putting 20V across that will draw a huge amount of current, and the LEDs will run hot. I chose instead to wire the strips in series. This gives as much light, but draws less current.
The light is intentionally purple. I use only the red and blue channels, since those are (approximately) the frequencies of light that plants can use. Said another way; plants are green because green is the only color they don't absorb. Adding green would give a whiter color, but add nothing for the plants while burning more power.
Underwriters Laboratories would not approve. Exposed soldered connections, no enclosure, and hand-wavy electrical engineering on an appliance that will be near water. Still, the power supply and LEDs run cool, and give intensely bright light.
We hang the lamp from a shelving unit in our living room. Underneath, we're sprouting Mustard Greens, Lettuce, Parsley, and Collards, and below that, a space heater to keep the seedlings warm. At least a month more before Jersey thaws and we can put them in the ground.