Zero Cost High Tech Interior Lamp

This article was first published in 2006.

If you like collecting the stuff that others throw out, here’s a near zero cost way of putting together a high tech cold cathode florescent light ideal for lighting the inside of boots, under the bonnet or even under the doors.

What You Need

Cold Cathode Fluorescent Lights (CCFL) are used in the instrument panels of some cars like Lexus, but there’s a much easier and cheaper way of getting them. Pretty well all flatbed scanners have them – it’s the light that travels along with the carriage when you’re scanning something. And even in scanners that have been thrown away, the CCFL most often still works.

The tube – about 2.5mm in diameter and the width of an A4 page (funny ‘bout that!) - is powered by a specific high voltage (HV) power supply unit. But this is usually very easy to locate – it’s the separate printed circuit board with just a handful of components on it that’s connected straight to the CCFL tube. Two wires lead to the HV power supply – a red wire (positive) and a black wire (negative). The CCFL usually lights at voltages above about 5V.

Note: The HV power supply develops hundreds of volts at very high frequency. The high frequency means that it is easy to get skin burns from the supply if you come in contact with it. Be careful!

The CCFL can be run straight off 12V but the tube gets warm and power supply will probably also get hot. Better is to drop the voltage to a more friendly 5 or so volts. This can be done with a high power resistor but a much more elegant way is to use the guts of a cigarette lighter phone adaptor. Many of these produce an output voltage of about 5V and can supply enough current. (Check the markings on the phone adaptor for the actual specs.)

Doing It

It’s a dead easy device to build. Open-up the old scanner and carefully remove the CCFL lamp and its HV power supply. The CCFL lamp will break if bent, so it’s best to keep part of the original housing to hold it securely. If you have a variable voltage power supply, connect up the positive and negative HV power wires and slowly turn up the voltage, checking that the CCFL lights. Bright, isn’t it?

Then open-up the cigarette lighter phone adaptor, paying attention to which wires are the input (ie nominally 12V in) and which wires are the output (nominally ~5V out). Connect the output wires to the CCFL power supply’s input, maintaining the correct polarity. Solder a pair of wires to the phone adaptor’s input, remembering that the centre pin of the plug is positive.

Check the system works by applying 12V.

It’s best to mount the HV supply and the phone adaptor in a small plastic box – remember, you don’t want to come in contact with the HV power supply! In our case, the two boards were held in place with double-sided tape.

Installation is just a case of placing the CCFL in the boot (or wherever you need the light), locating it so that it can’t be knocked. The power supply box can be mounted nearby. Feed power to the system from the original boot light (you can retain that light if you wish, or alternatively replace it entirely with the CCFL) and then wait for darkness so you can admire your handiwork. Wow, a florescent lamp in the boot!

Easy, huh?