Just a few tens of nanometres across, they are among a growing array of 'nanolights' that researchers are tailoring to specific types of fluorescence: the ability to absorb light at one wavelength and re-emit it at another. ... Many naturally occurring compounds can do this, from jellyfish proteins to some rare-earth compounds. But nanolights tend to be much more stable, versatile and easier to prepare — which makes them attractive for users in both industry and academia. ... Nanolights have already begun to find application in areas ranging from flat-screen displays to biochemical tests. And researchers are working towards even more ambitious uses in fields such as solar energy, DNA mapping, motion sensing and even surgery. ... Light is emitted when electrons are kicked up to higher energy levels by some outside source, such as ultraviolet light, then fall back down to lower levels.