Simple RGB Cold Cathode Light



Introduction: Simple RGB Cold Cathode Light

This project started because I needed a 90 degree HDMI adapter but just couldn't bear to leave Monoprice with only a $3 very boring widget. So, after combing around for a while I found these cold cathode tubes designed for lighting up your PC. I bought one each in red, green and blue and after about 20 minutes of assembly had a pretty decent little lamp. Total cost was about $25-30.

Shall we begin?

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Step 1: Materials List

This is a very simple project so all you'll need is:

- Red cold cathode tube kit
- Green cold cathode tube kit
- Blue cold cathode tube kit
- 12V DC power supply
- Scotch tape
- Electrical tape
- Foam insulation tape
- Translucent tube of your choice


The cold cathode kits I had included an inverter, a switch, and all the wiring. They're designed to simply plug in to your desktop's molex connectors so they should be all ready to go.

The red kit had 2 lamps included which worked out for building but gives the light a pinkish hue when in white mode.

The tube I used was from the center of a roll of large format printer paper. It is a translucent, whitish plastic with small striations along the length.

Step 2: Assembly

1- Scotch tape the cold cathodes together. Because I was using 4 lamps, it formed a tidy square about 1-1/8" on a side. The tube was about 2" in diameter so to fill the gap, stick that foam tape on there.
[The lamps were arranged so the two red were not directly next to each other.]

2- Cut the tube to length and cut a small notch out of one side for the wires.

3- Insert the lamp bundle into the tube. Squeeze the foam to help get it in.

4- Wire up the leads from the inverters in parallel. These cold cathodes use the 12V line from your PC's power supply so I grabbed a 12V wall wart and hacked it in. And remember: red to black, venom lack; red to yellow, kills a fellow. Or something like that...
Seriously though, if you don't know enough about electronics to confidently wire this device please get some assistance from someone who does. It'll be well worth your while.

Step 3: Hittin' Switches

Now plug it in and give it a go.

With this configuration you can get 7 colors:
- Red
- Green
- Blue
- Orangish (red & green)
- Purplish (red & blue)
- Cyanish (blue & green)
- Whitish (red & green & blue)

[The phone cam I used for the pics blew out the color on the tube, so you'll have to look at the wall behind it for estimations of color.]

The colors aren't very pure or distinct due several factors including:
- The configuration of the array, which produces different hues depending on the angle of the viewer relative to the tube.
- The relative brightness of the different cold cathodes.
- The color (wavelength) of the cold cathodes.

Despite this, the light turned out to be a nice quick and easy project, I think.

A few final notes:
- I'll soon get a hunk of wood or something and cut out a hole the same size as the outer diameter of the plastic tube to make a stable base. Probably a good idea to keep it from toppling over and will also provide a place to situate the switches.
- The packaging indicated that the draw of the cold cathodes is about 5mA (I'm assuming that includes the inverter). There wasn't much info about this with the product however, so I just used the 800mA power supply I had on hand. If anybody can address any problems with powering this setup, or just provide more info as to minimum current for the power supply I would appreciate it.

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