Magicolor Shadow Lamps

Blending colored light beams is absolutely amazing and fascinating!  By hacking three (extremely cheap) Ikea spotlights into red, green and blue light sources, you can make a fascinating science experiment set-up or museum exhibit.

There are two things about this experiment / activity that I really like:
- It's attractive and educational for all audiences: for toddlers and grandparents, college students and high school kids.
- The lamps give a great opportunity for kids to explore and wonder, without the direct need to "produce the right answer".  

In the video, three 10 year old Dutch girls explore the lamps and the way the colors mix. They unravel the mystery of the yellow shadow by themselves, by covering the lamps one by one. I only interfere by asking questions about what they observe. The conversation in the video between the kids and me is in dutch. I'll add english subtitles later on...

• Pupils get the opportunity to explore a phenomena connected to light and/or color, initially in a way of their own (when using the lamps during a class, focus on one phenomena at a time).
• Pupils learn to closely observe an "scientific" event.
• Pupils analyse the properties of colored and white light by manipulating different light sources and combining them. Analysis is facilitated by letting the pupils work in small groups (3 pupils). 
• Pupils structure and reflect on their findings by verbalizing their thoughts to each other and preferably also to a teacher.
• By letting the pupils have a presentation of their findings, in which they use the lamps again, they learn to structure information, cooperate in a group and present themselves to an audience. The lamp now functions as a tool to demonstrate a phenomenon.

• How white light is made up of primary colors red, green and blue
• How red, green or blue light can blend into other colors (yellow, cyan, etc.)
• How blending colors of light differs from blending colors of paint (additive blending vs subtractive blending) 
• How shadows appear, and how the shape and brightness of a shadow changes when the light source is moved to and from an object.
• [add your own here]

The stuff you need for making three rgb-spotlights is pretty straightforward. I used:

Stuff:

• Three Ikea Jansjö spotlights (Ikea US, Ikea NL). I bought them for €5 each as a discount item. Regular price in NL is €10,-
• Leds: red, green and blue. I used 5mm superflux leds because I already had them. Beside the leds, you also need the specifications of the leds, which are easy to find on the internet. More generally speaking: You need superbright leds with a flux of around 4 lumen for red and green, and 2 lumen for the blue led. Red and green leds are around €0,50 / US$ 0,70. Blue leds cost around €1,50 / US$ 2,-
• Resistors to adjust the current through the leds. I used 22 Ohm for the red LED, and 10 Ohms for the green and blue LEDs. More on calculating the resistor-value in step 3.
• A plastic sheet, 2mm or so thick

Total costs shouldn't exceed €35 / US$50
Leds and resistors can be bought at Conrad, Farnell or RadioShack

Optional:
If you want to be able to dim the lamps (step 8 and further), for each lamp is needed:
- 2x capacitors 10 nF
- 1x transistor BC547(B)
- 1x transistor BC557(B)
- Resistor 5k6 (or 4k6, if you want to dim the leds to zero)
- Resistor 10k
- Resistor 330k
- Potentiometer 50k

- Jumper wire
- Nuts, bolts and spacers to mount the pcb in the casing.

I haven't finished building the dimmers yet. The prototype circuit in step 8 does work, however.

Tools:

• Soldering iron and solder
• Fretsaw
• File: a small one with sharp corners (I used a file with a triangular cross section)
• Drill and drillbits: 1.5mm and 12mm
• Screwdriver (philips screw)
• Straight screwdriver or blunt knife to lift the lens cap from the spotlights.

The first part might be the trickiest: How to remove the lens from the holder, so that the led inside the lamp becomes accessible / removable. have a look at the pictures...

Picture 1:
The lens is hold by a plastic translucent ring, which fits (snaps) over a white reflector. By removing the ring, the reflector becomes accessible and removing the led is then easy.

Picture 2:
To remove the ring: Be careful, gentle and patient. Wriggle a flat screwdriver (or a blunt knife) in the slit between the rim of the silver colored holder and the translucent ring. Carefully lift the ring, until it snaps loose.

You need some (gentle) force and persistance to get the ring loose. If you'r unlucky enough to break the ring, you'll need to find a way to glue it back later on. Or buy a new lamp for five bucks :-)

Picture 3:
The ring and lens are removed. The white reflector covers the white led.

Picture 4:
Remove the white reflector by unscrewing two philips screws on the sides. The pcb becomes visible, on which the led is mounted.

Picture 5:
Desolder the power wires from the pcb. Not a hard job, grab a wire with small pliers, and melt the solder around the wire on the pcb with a soldering iron. Pull the wire gently loose when the solder melts.

Picture 6:
The pcb is glued on two ridges inside the lamps' frame. Wriggle it loose with a knife or screwdriver. You won't need the pcb for this project, so don't panic if you break it.

Picture 7:
Exploded view. 

... and Ohms's law!

In this step, the leds are prepared to shine just bright enough to be ensured they will last for a while. To do that, the current through the led must be limited to an appropriate value.

There are two ways to do this: By trying and finding out (with the risk of burning a $2 led), or by calculation.

By try and find out:
If you have a supply of different resistors, a power supply at 4 Volts and a breadboard, you can just put a resistor in series to the led and observe how it shines. Start with a 150 Ohm resistor and decrease the value from there.

Specs!
The current that's ideal for the leds you use can be found in the specifications that go with the type of leds you bought. The ideal currents differ with the color of the led! So chances are you need three different resistors for your red, green and blue led (but my guess is that the value for blue and green will be the same...)

The Voltage that is ideal for the led can also be found in the specs. Again, expect differences between leds of a different color.

Ikea's power supply is really a Voltage supply: It keeps the voltage between the white and black lead at 4 Volts, as long as the current through the circuit stays under 0,75 Ampere.

To calculate the value of the resistor needed for the led, you need this formula:

R = (4 - U_Led) / I_Led
R = value of resistor (in Ohms)
U_Led = Optimal Voltage for the led (in Volts): In my case: 2,8 Volts
I_Led = the optimal current through the led (in Amperes). In my case: 50 mA, which is 0,050 Ampere.

So the resistor I needed to let my red Led shine brightly without burning it is:

R = (4 - 2,8) / 0,050 = 24 Ohms.
I used 22 Ohms, the closest value I had lying around.

My green and blue leds work fine at 3,9 Volts and 0,070 mA, according to the specs. Because 3,9 Volts is so close to the power supplies' 4Volts, I didn't really need an extra resistor. I added one just to be sure, with a very small value: (4 - 3.9) / 0.070 = 1,43 Ohms, which became a 2 Ohm resistor.

Soldering
To mount the led and the resistor into the lamp casing, you need to solder the led and resistor closely together. I strongly suggest to use a third hand for that. Make a third hand yourself: here or here, or buy one for a few euros / dollars at Farnell or RadioShack.

Please keep in mind the polarity of the leds: With most types of leds, the minus-side is indicated with a bevel.

To fit the led with the resistor into the lamp housing, the white plastic refelector must be adjusted. With the type of leds I used, I had to make a larger, square hole :-s

I widened the existing hole in the reflector with a 12mm drill bit. Then, with a triangular shaped file, I patiently filed the round hole into a square one. it took me about 10 minutes to get it done nicely.

Make the square hole large enough so that the leds casing fits nicely into it. Have a look at the pictures to get the idea.

To mount the led and resistor into the lamps' casing, a platform is needed instead of the pcb that was removed in step 2.

I used plastic sheet for the platform. The sheet I used is white ABS, 1.5 or 2 mm thick. I bought it at a crafts store, ages ago.

Picture 1:
The shape of the pcb can simply be traced onto the sheet. For the notches, I simply drilled holes in the sheet before sawing the platform out of the sheet (sorry, I forgot to take a picture).

Picture 2:
In the center of the platform, the led will be mounted. To make sure the led is mounted as closely to the platform as possible, I drilled 4 small holes (1.5 mm wide), corresponding to the led's four leads. To get the right spot for the holes: Fit the led into the reflector and place it over the platform. Push the led firmly into the plastic platform. The leads will leave small pits in the plastic.

Almost done, really!

What can go wrong now is mixing up the power supply's positive and negative lead with the led's positive and negative leads.

From the lamp: Black is the negative lead, white is the positive lead.
The led: The positive and negative leads were determined before.

Mount the selfmade plastic platform into the lamps' housing, and place the led into the four holes. Let the led's negative lead face the power supply's negative lead. I screwed this up with two (yes, 2) of the three lamps I made. Really, I did.

Solder the power supply's leads to the led. easy soldering, because the leads are already fixed by the lamp's housing and the plastic platform.

Then place the reflector over the led. A little wriggling might be needed to get the wiring comfy under the reflector. Then fix the reflector with the two screws.

Finally, replace the lens and translucent ring over the reflector. You're done!

That is to say, you need to do this three times: For a red lamp, a green lamp and a blue lamp of course! So repeat steps 2 through 6 two times more. You'll be faster very round, I promise!

When you actually made a red, green and blue Ikea spotlight, this is what you got.

Is this the end, then? Well, no. For classrooms, it would be nice to have the three spotlight into one device, with only one powerplug. And it would be nice to be able to adjust the brightness of the separate colors as well. In the next steps, I'll describe how to make a led dimmer for the leds (which was tricky, because the power supply's limited to only 4 Volts), and a casing for the lamps...

For the dimmer circuit of _one_ lamp, you will need:
- 2x capacitors 10 nF
- 1x transistor BC547(B)
- 1x transistor BC557(B)
- Resistor 5k6 (or 4k6, if you want to dim the leds to zero)
- Resistor 10k
- Resistor 330k
- Potentiometer 50k

- Jumper wire
- Nuts, bolts and spacers to mount the pcb in the casing.

Since we're making a red, green and blue lamp, three times this bill of materials is needed :-s