(Project completed: 2012-01)
For a while I've been needing some bright lights for my macro photography, and also wanting some bright color accent lights. I bought this from ThinkGeek. It has the advantage of simply plugging into a standard light socket, and has sixteen different color settings. I found it still a bit too dim, and some of the colors were off - blue especially looked too purple for me.
So I decided to make my own - a larger one using multiple super-bright LEDs of four colors (red, green, blue and white) arranged in a Chang mosaic with a diffusing filter in front to mix the colors. With this arrangement I should be able to get a much better variety of colors, and using multiple LEDs would give me more brightness.
I based the physical design around available enclosures, protoboards and power supplies. I don't like working with high voltages (they tend to be a bit killey) so I'll always use an off-the-shelf power supply if I can. I decided on a 12V, 1A supply I had on hand because using a higher voltage would let me place the LEDs more in series, thus reducing the current requirements and the number of current limiting resistors I would need. Most super-bright LEDs have voltage drops between 3V and 4V, so that let me put them in series of three.
Here's the schematic (click to embiggen):
I decided to socket the LEDs in female header strips instead of soldering them to the protoboard, in case I burnt some of them out and needed to replace them. In practice this perhaps wasn't such a good idea; it complicated the physical layout of the circuit on the protoboard, and generated problems with loose connections between the LED leads and the sockets. I could probably solve the latter problem well enough by bending the ends of the leads slightly, but it seems to work well enough if I don't shake it too much, and it's easy to fix if a connection fails.
Here's a picture of the finished board, populated with LEDs, installed in the enclosure I picked for it.
You can see the four brightness control potentiometers installed on the sides. At the bottom is a cheap tripod mount I made with a quarter-inch bolt and bolt joiner.
The next picture shows the reflective, scattering backdrop I put the LEDs through to help blend the colors. Since I was planning to put a diffuser in front of the LEDs, I figured there would be a lot of light back-scattered and so I should put a reflector at the back to stop some of the light from being wasted.
I also added the color-coded knob handles to the controls in this shot.
And finally, here it is with the diffuser on the front:
I made the diffuser myself by cutting a thin sheet of clear Perspex to size, then grinding both sides with coarse and then smooth sandpaper. It worked out well.
Although I had intended the light to be mounted vertically on top of a tripod or light stand, someone pointed out to me at this point that it could also be used horizontally as a small light table. It kind of looks like a disco floor when used this way:
And now, the results! To see if my project achieved its goals of brighter light and better color than the light I bought from ThinkGeek, I shot the following series of images (click to enlarge please). All images were shot using the same exposure and a fixed color temperature of 5400K. The upper row shows the primary colors of the ThinkGeek light, and the lower row is mine. Mine has an extra photo for white - the dim one is just the white LEDs, and the bright one is with all LEDs on at full intensity.
Overall I'm very pleased. It's one of the better electronic projects I've done in terms of polish (ie putting it in a finished enclosure with mounted controls etc). It works, and may prove useful in my photography, as intended. Best of all, completing it gave me a much-needed feeling of having finished something for once. If I were to make another one, I would lay out and etch the circuit board myself rather than using a protoboard, so I could get more control over the spacing of the LEDs and the arrangement of the traces. I'd also solder the LEDs in instead of socketing them.