Intro: Rainbow Maker
A simple gadget to create rainbows for light painting. It can also be used in other interesting ways to light paint big areas of something or thin air. Photography is made in low ambient light - at night in an open space where you can move freely. The exposure is not critical, on this pictures it varies from 30sec to couple of minutes. Check damngood facebook page for more ideas...and YES, the picture no. 5 (DARK SIDE OF THE MOON) has a WRONG DISPERSION - the red should be on the top :)
Step 1: Gather Materials
The first thing is to find a way to power 20W RGB led strip. I use a battery from a cordless drill - basically a battery pack of 18V. The LED strip is designed to be operated at 12V so you will need some resistors to lower the voltage from 18V to 12V. Three colors with simple light mixing can give R, G, B, RG, RB, BG and RGB color (that is 7 different colors). To use this combination of colors you can connect three push-button switches in parallel with each color and the battery. I didn't have much time or nerves to make a "nice" controller so i just used a piece of wood (you will see it in the next step). Assembling the controller by soldering and hot gluing on the wood. On the other hand this is operated on 18V so there is no danger in e-shocking yourself. Maybe you will kill the battery if you short circuit it in some time while building this so BE CAREFUL on this!
Step 2: Glue It All on a Piece of Wood
Ok so here you can use some prehistoric methods to make things hold as strong as possible at place. Hot glue actually sticks very good to untreated wood. Solder everything according to the scheme. Here is a little catch: RGB colors usually don't shine with the same intensity (or maybe my LED strip is made with some mistakes) anyway you should experiment to see how much a certain color should receive current to mix with the other colors with the same amount. You control the current by changing the resistance in the branch with a particular color. On the end you have to get R+G to give yellow and R+B to make violet. In my case this is as shown in the sheme: the R branch has 40Ohms and G and B have 120Ohm each.
Step 3: Ready to Paint Into Thin Air
On the end I have put the LED strip on another stick and fasten it with some isolating tape (I didn't have ordinary tape) but I doesn't matter cause it is used in the dark. Wait for the night to come and you can start your paintings. The rainbow is made with a stick that was laying on the ground to have a fixed point of rotation of the led strip. The battery pack can be tied to the waist so you can freely run and move holding the controller in one hand and the LED in the other.
You will have to set the exposure as long as you need to make the light painting, so you have to do this at night. The pictures shown in the introduction were taken in Belgrade at night, on the fortress Kalemegdan.
And remember the rainbow sequence of colors:
RED+GREEN = YELLOW
GREEN+BLUE = CYAN
BLUE+RED = MAGENTA
RED+GREEN+BLUE = WHITE