The Lighting Show PLASA is from Sunday 10th to Wed 14th Sept 2011 at Earl's Court.
Concentrating on the technology of lighting there are a number of excellent lectures by some of the "best lighting designers around". It is a bit of a geek-fest but if you're into stage, television or film studio lighting it's worth a visit.
PLASA 2011 - Live at Earls Court 11-14 September 2011
For video equipment Broadcast Video Expo (Formally Broadcast Live) in Feb 2012 is probably a better bet.
Broadcast Video Expo 2012