Every restaurant kitchen in the country has been sold a UV fly killer. Several UV flurescent tubes with an electrified grill in front. 'The flys are attracted by the UV and fly into the grid and are electrocuted'.

But are they?

Damien Hirst has produced two art works using live swarms of flys 'A Thousand Years' and 'Lets Eat Outdoors Today' (currently showing at the Royal Academy). Both feature thousands of free flying house flys in a glass enclosure with a large UV fly killer.

In both installations the flys take absolutely no notice of the UV whatsoever - any that are killed just happen to fly into the electric grid as they buzz randomly around.  This is immediately evident to anyone who visits the Royal Academy show - go and look!

Do the makers of these machines back their claims with any scientific evidence?

If you have a current going through a fluorescent bulb tube and you smash it, for a split second there is a yellow flash as the gas escapes. What I'm wondering is what causes the yellow flash if the light coming out originally is a mix of colours that make white light?