Yes they do work. I use one of these
http://www.gadgets.co.uk/item/X5TORCH/Inova-X5-LED-Floodlight.htmlIt isn't the best due to it being quite small and low power (probably not as good as the other one already linked on this thread). However, in its favour, it is quite cheap, it is surprisingly good when you close all the curtains, it is very portable (pocket size) and it is very well made.
Do not buy a mains only light as this is a faff with trailing leads, searching for sockets etc. Make sure the light does not have a warm up time (some do and it is frustrating). Also, make sure that it is a light that does not get hot (I know someone ho burnt a carpet with one).
Another thread could be how to use one, how to involve your customer and how to use it for urine call backs (i.e. identifying new urine marks/odour when the customer claims it is your failed attempt).