Chemists at the University of California have devised the world's smallest electric light bulb: small enough that fifty thousand of them side by side would be no wider than a human hair.

The "nano-bulb", barely one nanometre (a millionth of a millimetre) across, is made from soccer-ball-shaped molecules, each of sixty carbon atoms called buckminsterfullerene, or, colloquially, 'buckyballs'. Discovered in 1985 and first mass-produced in 1990, buckyballs were once famously described in the British House of Lords as doing nothing in particular and doing it very well. Now buckyballs have proved themselves capable of doing something after all.

To imagine a buckyball, think of a spherical carbon cage whose sixty atoms are located at each corner of the six-sided and five-sided leather patches on a soccer ball, only about a hundred-millionth the size. The resemblance to the geodesic domes of US architect Richard Buckminster Fuller gives the molecule its nickname. Because of its round shape, one of its discoverers Sir Harry Kroto of Sussex University predicted that the C₆₀ molecule would usher in a new kind of "chemistry in the round".

It is possible, for example, to attach chemical groups to the surface of the carbon ball. In this way, researchers have been able to make such exotic items as buckyball necklaces and pendants, in which the balls are linked into long chains. Researchers in California, led by Fred Wudl in Los Angeles, have attached six so-called pyrrole molecules to the C₆₀ cage, which protrude like three sets of ears.

This molecule, which they call THP, is fluorescent: it absorbs and re-emits light. This led the researchers to wonder whether THP might serve as the light-emitting material in a light-emitting diode (LED), which can be switched on and off electrically. LEDs are ubiquitous in modern technology: just about anything that glows on your hi-fi system will be an LED.

Most LEDs in use at present are made from inorganic semiconductors such as gallium arsenide phosphide. But LEDs made from organic – that is, carbon-based – substances might offer several advantages, such as low weight, low cost and ease of fabrication. Many companies are attempting to make LEDs based on organic polymers, and at least one such – Cambridge Display Technologies in the UK – is on the verge of producing a full-colour TV screen based on these organic light sources.

A fluorescent substance offers some prospect of being useful in an LED – but the trick is to make it emit light when stimulated by electricity, not by light. This is what Wudl and colleagues have managed with THP. They mixed it with two organic substances that can conduct electrical charges: one to carry negative charges (electrons) and the other to carry positive charge (so-called 'holes'). These conducting materials also emit light themselves when electrically stimulated.

As Wudl and colleagues report in the Journal of the American Chemical Society, thin films of this mixture glowed with white light, which became coloured if one of the components was left out. White-light LEDs are particularly useful because they emit across the whole of the visible spectrum, and so can generate any colour of light simply by using coloured filters. The bucky-ball LEDs remain very inefficient at present – only a small fraction of the electrical energy gets converted to light – and they operate at voltages much too large for commercial use. But it is a promising start for the bucky bulb.