I'm not sure if I'd ever heard the phase "son-et-lumiere" before but, according to Wikipedia, it's a sound and light show which takes place in a historical location. That's what is going on here. This is Space, The Universe and Everything by Luxmuralis which took place in St Martin In The Fields and saw the history of science projected on the side of the building, footage from Apollo 11 projected in the crypt, stars filled the room where you'd usually find the cafe - and this is just before the grand finale - which culminated in a spaceman with a picture of the earth where his face should be projected on the Apse. Arty.
