Blue is cool. Blue is also the preferred color for us theatrical types and other people who have to work in the dark without shining annoying lights around. It's either blue or red, and there's a trick about blue:
The trick is, that "White" LEDs are mostly blue LEDs (or UV) in a phosphor doped case. The case glows yellow, the LED glows blue, and the combination fools the eye into thinking it is "White." (Look at something green under a white LED some time.)
Which means, to within an acceptable margin of error, a bright blue LED will have the same electrical characteristics as a white one.
(For some projects, like my blue night light, there was a slight difference in forward voltage that was enough to keep the photocell from turning the light off during the day. Fortunately, a common IN4001 diode in series with the LED added enough of a voltage drop enough to fix that.)
For this Instructable, we will be modifying a very cute miniature generator flashlight from RadioShack.
Step 1: Parts and Tools
Our victim for this experiment is this "mini cranking light" from RadioShack:
For a replacement, we need 3mm bright blue LED's. The ones I used are from the local electronics store; they were apparently 900 mcd (the marking on the bin was a bit hard to read) with a forward voltage of 3.2 to 3.4V.
In a previous adventure (I rewired my night light) I had to add a series diode to drop the voltage just slightly (the photosensor switch wasn't activating properly with the new LED).
You will also need the basic tools; at least a small phillip's screwdriver, a soldering iron, and solder. A de-soldering pump and a third-hand jig are also very handy for this project.