Can you use a french light in a uk socket?

Yes, the voltage and frequency of the supply is the same, but you will need an adaptor to be able to plug it in. Get one from a travel shop in the UK. Another way that I use is to buy a French plug and fit it to a UK extension socket, you can then have up to four UK appliances on at the same time, which can be useful if you have a mobile phone, a computer, a shaver, a camera, etc. But don't do this unless you are confident about making electrical connections, the French plugs are a bit tricky inside.