What is going on with the shape of lightbulbs these days?

Take the reassuringly familiar incandescent light bulb. In essence, the same design that Humphry Davy first unveiled in 1809 - two wires connected to a battery, touching the ends of a filament with high enough resistance to heat up and glow (latterly, tungsten). And the bulb stops oxygen getting in, which would make the filament burn up.

So why are compact fluorescent lightbulbs such weird shapes?

Because they work completely differently. In incandescent bulbs, brightness is dependent on how the filament emits energy (around 10% of which is light - the rest is wasted heat). In CFLs, brightness is all about area. Here's why. In a CFL tube, a current is run through a gas, and ultraviolet light is produced. That UV light bounces off a coating of phosphorous lining the inside of the tube - making it glow or fluoresce. The more tube available, the brighter the overall glow.

And that's why CFLs are manufactured in such crazy loops, swirls and whorls - trying to get the longest length of tube packed into the smallest space. These are the three designs you'll be most familar with by now:



(Image: Plumen)

The middle one - yes, we're back to that old design, is hiding the loops inside a standard bulb. And what a shame, when fluorescents are such a creative opportunity. Look how much fun the Plumen Project is having. CFLs can be any shape. That's a challenge: fit your lights to your room, not the other way round. Experiment with your eco-lighting (and play with the dark).

By the way, CFLs are nothing compared with how much fun LEDs will be.

Image: Paul Keller