A thing I have finished

I’ve been craving a feeling of accomplishment for a long time, and I promise myself that over the Christmas holidays I would make an effort to finish at least one of my personal projects.  And I did!  And it feels good.

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 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.


  • Mine is not as much brighter as I had hoped (perhaps half a stop for individual colors) but it is still brighter. The full-on white is considerably brighter.
  • Mine has a slightly more bluish blue.
  • The diffuser/reflector arrangement worked out well; when used as subject lighting rather than as a light table, the color mixture is very smooth.  I could get more brightness by using a clear front panel instead of a diffuser, but then the colors would be less evenly mixed.
  • Mine consumes slightly more power (9W versus their 7W) but that’s not a huge difference.
  • Mine can produce a much wider variety of colors by virtue of having separate analog brightness controls for each of the four color components.
  • Mine produces softer shadows on small objects because the light-emitting surface is relatively large; the ThinkGeek light is almost a point source so gives hard shadows.
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.

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