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.
Step 1: Materials and Tools
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
Step 2: Build the Box
The box is just of basic construction and you can build anyway you like. As I mentioned, I used mostly what I had on hand so it might not make sense. The sides are 1" (0.75") pine which are glued to the 1/2" (0.5") front panel. This gives a U-Shape 'chassis' to start with. The lamp socket plate is glued to the front panel about 3 inches up from the bottom with about 1/8" gap on each side next to the side panels.
One unique feature in the box is that I included a ventilation opening in the bottom that also acts as access to the hidden on/off switch. The ventilation opening also has the switch box and socket plate alternated (make a zig-zag path for the air) to reduce light leaks.
The top panel is glued into position and the back access panel is held in place (with a 1" opening at the top) by 4 countersunk brass screws
Step 3: Paint the Insides Flat Black
Mask off the edges and paint the inside of the box flat black in order to reduce light reflections.
Also paint the inside surface of the rear access panel.
Step 4: Prepare Lamp Socket
The lamp socket I had was the type intended to me mounted to threaded lamp pipe; so I had to remove the bracket for pipe. This can easily be done by inserting a screwdriver into the socket (always disconnected from electricity) and remove the screw holding the bracket in place. The bracket can be removed and discarded. The lamp socket wires can be routed in the groves made for them so that the socket can be mounted to a flat surface. A #6 x 1" screw will be inserted into the hole the bracket mounting screw came out of when we end up mounting the socket.
Step 5: Assemble the Electrical
I cut the 'wings' (mounting brackets) off of the blue plastic single-gang box so it would fit in-between the side panels. I then drilled a hole in the side of the box just large enough for the extension cord, which becomes the projectors power cord, to fit through. I also drilled two holes in the end surface of the box in order to take two mounting screws. The box will be screwed down to the side panel about 1" above the bottom.
The electrical switch is too long to fit between the side panels, but the mounting brackets on it are scored so that they can easily be broken off with pliers.
Cut the receptacle off of the extension cord and strip the wires. The cord is threaded through the hole in the side of the switch box. I tied an overhand knot in the cord to keep it from coming out or putting strain on the internal connections. Drill another hole in the opposite end of the box for the lamp socket wires to enter. Tie an overhand knot in them also to prevent them from pulling out of the box.
The extension cord is 'zip cord' and if you look closely and feel, the cord has one conductor where the insulation is rounded and smooth and the other conductor has a ribbed surface. This ribbed surface indicates the conductor connected to the wide blade on the plug. This is the 'neutral' conductor and is the conductor that should be connected directly to the screwshell (threaded outside ring part) of the lamp socket. The smooth conductor is the 'hot' conductor and should be the one that is connected to the switch and then on to the center contact of the light socket.
Step 6: Mount the Socket and Electrical
The blue plastic switch box is screwed down to the side panel using two #6 x 1/2" pan head phillips screws. They go through the box in the two holes drilled in the end. The lamp holder wires are routed through the gap between the socket plate and the side panel. The socket is screwed down with a #6 x 1" screw that goes into the hole the mounting bracket screw came out of. The socket is fastened so that it is located centered side to side and front to back to the walls of the box. The switch cover plate is cut to size so it fits the box and covers the wires inside.
Step 7: Install the Lamp and CD-R Section
The lamp is screwed into the socket. Cut the CD-R with the aviation snips or use a fine toothed saw. The resulting piece should be just slightly wider than the distance between the side panels so that the disk will fit if flexed slightly. It should be positioned about a 1/4" from the LED lamp centered on the lamp, but tilted slightly.
Here you have to play around with the disk material to see how it reflects and where the 'sweet spot' is located. Once it is performing well the rear access panel can be screwed into place with the 4 brass screws.
Step 8: Install the Mirror
Observant folks will notice that the 'rainbow' has the color order reversed. Violet should be at the bottom. Of course it depends on your vantage point what is 'bottom'.
However, to 'correct' this 'error' I plan to attach a acrylic mirror to the exit window so that the colors can be projected onto the ceiling in the correct order. The mirror will also have some adjustability so that it is easier to aim the rainbow where you want it.
Step 9: Finish the 'Cabinet'
The cabinet can now be finished with your choice of method. I used a all-in-one stain and polyurethane. Use a finish to your liking.
Step 10: Enjoy
The Rainbow Projector is done! Now you can fire it up and shower your walls and ceiling with the colors of the rainbow. The projector is intended to be operated vertically sitting on a flat surface, but it can be tilted on its side if desired. The vertical orientation was intended to keep the LED lamp running as cool as possible - both to insure there is not fire hazard and also to extend the life of the LED lamp, as cooler running lamps last longer.
Thats about it! I hope you enjoyed bringing a bit of a rainbow indoors!