To mark Earth Day 2012, a new kind of light-bulb is going on sale in the US.

(What makes this light-bulb different is that it lasts for 20 years. They are made by Dutch electronics firm Philips. The bulb swaps filaments for light-emitting diodes to provide illumination.

Using LEDs endows the light with a long life. The downside is the hefty price tag; the first versions are set to cost $60 (£37).

Why is being green always so expensive?)