cold cathode

The common name for a Cold Cathode Fluorescent Lamp (CCFL). Thus called because, unlike standard "Hot" fluorescents (e.g. The colloquial “neon” light), they require no heating filament. Cold cathodes are many times brighter than the standard fluorescent bulbs while maintaining a much smaller diameter. They also require a much higher voltage to run, and are more reliable due to the lack of a filament.

Cold cathodes have gained popularity of late as the lighting of choice for "case modders", those who enjoy tricking out their personal computer cases. Usually matched up with a window kit, to show off the inside of your r33t system, and to provide an eerie glow in the color of your choice emanating from your case. While actually referring to just the bulb or tube, it usually is used to mean a complete setup, including inverter and power supply ready to be plugged into your standard ATX case.

The Cold Cathode Fluorescent Lamp is also an item of prime importance for a great number of LCD screens--particularly those used as monitors, externally or in laptops. The number of lamps in these monitors can vary, as can their size. They are hard-fastened as part of the LCD panel proper, on either the edge(s), the top/bottom, or any combination of these. The inverter boards for these types of lamps can generally output varying levels of power, thereby allowing the screen to be dimmer or brighter.

The lamp itself is very thin, usually around three to five milimeters in diameter, from experience. This makes it a very fragile piece of electronics. Lead wires at each end attach to the inverter. The lamp is mounted in a highly-reflective piece of metal, which is then affixed to whichever edge of the panel it is meant to be affixed to. The light (which is extremely bright, as has been mentioned) will be shone over a glass plate behind the rest of the LCD panel's components. The glass plate itself is in front of a white sheet, and may also be opaque (fogged) on one side so as to diffuse the light proper.

Failure of these lamps or the inverter can cause various problems, including, but not limited to: dark/black screen (the liquid crystal display will still function, but with no light, it will be nigh-impossible to read), coloured screen (failure can cause the lamp to glow at an off color; ie, red), and such.

Finding replacement CCFL tubes is a hard task; installing new tubes is difficult as well, and carries the risk of dismantling your LCD screen entirely, and taking great care to not break your new bulb. (Some bulbs come unsoldered; others come with leads attached, as an aside.) It is also dangerous, in that the inverter puts out a great deal more voltage than you might expect. Hence, the DANGER: HIGH VOLTAGE sticker that you may see affixed on the innards of your LCD screen, once you ply it out of the laptop.

But then again, they're pretty cool to turn on once removed, if the bulb/inverter is bad, and it's turned reddish orange.

Edit: I managed to replace my own. Mouser Electronics sells the bulbs. See my FAQ at my second home.