There is nothing quite like the majesty and splender of a huge vivid rainbow on a bright day after a storm. Unfortunately rainbows seem to be more than a little uncooperative when trying to coax them indoors. All I wanted was nature's splash of multicolored light on the ceiling. But it turned to more difficult than anticipated.
I tried the traditional prism approach but the projected spectrum was way too small. I looked at commercial offerings - the one that seemed to give good results was battery powered and didn't project the spectrum at all but 'faked' a rainbow by projecting individual colored LEDs. I considered purchasing diffraction grating but wasn't sure what I'd get. I read about mirrors in trays of water and splitting open DVD-RW disks and pealing off metallization with packaging tape. But ultimately I ended up with something much simpler... I ended up with this Instructable!
My Rainbow projector is based upon what I had around the house. The main component is a LED PAR (spotlight) bulb and an unused old CD-R disk. I wanted to make the projector smaller, but the physical size was based on the LED lamp which I already had so unless I wanted to spend more on a new lamp I was stuck with something a bit larger than ideal, but still very nice. The projector is about 12-1/2" tall and about 5" square. The on/off switch is hidden inside the ventilation opening at the bottom.
LED 7w PAR replacement (You must use an LED lamp as incandescent would generate too much heat and be a fire hazard. Also, the lamp needs to be the type with a single light source, [you can see one large yellow dot in the center] not the type with multiple LEDs.)
Unused CD-R (Other disk types might work but this did without any modification, except cutting down to size.)
Wood case (Most of the wood I had lying around so don't try to make any sense of it)
2 - 1" x 5" x 12" (0.75"x4.5"x12") pine - Two Side Panels
1 - 1" x 4" x 3-3/4" (0.75"x3.5"x3.75") Pine - Lamp Socket Plate
1 - 1/2" x 6" x 12" (0.5"x5.5"x12") Pine - Front Panel
1 - 1/4" x 6" x 10" (0.25"x5.5"x10") Poplar - Back Access Panel
1 - 1/4" x 6" x 5" (0.25"x5.5"x5") - Top
1 - Plastic Single-gang shallow remodel electrical box (the blue box)
1 - Single Pole Switch (your regular run-of-the-mill switch)
1 - Light Socket with lead wires
1 - Wire Nut suitable to joint two 18AWG wires
1 - Household Extension Cord (of the length you would like the cord on the Rainbow Projector)
1 - Wall Switch Plate single-gang. I used an 'end sectional plate' (the kind for custom multi-gang plates) since it was super narrow to fit in my tight space. However, I did have to cut it down; so in hind sight I would just purchase a regular plastic ('won't shatter' nylon) plate so you can cut it down.
1 - CD-R unused disk
1 - #6 x 1" pan head phillips screw to mount socket
2 - #6 x 1/2" pan head phillips screw to mount switch box to side panel
4 - #6 x 3/4" flat head phillips brass screws to fasten rear access panel in place
Black Spray Paint
Mirrored Acrylic (Optional)
Saws for cutting wood
Clamps for clamping wood pieces while glue sets
Aviation Snips (cutting off wings off electrical box, cutting down switch cover, cutting down CD-R)
Drill Motor/Drill bits