Sorry if I didn't make myself clear. I'm in total agreement that it's the updating process rather than the names where the problem has it's roots. I found it very interesting to discover the effect of renaming purely because it goes a long way to prove that there's a problem which occurs only during light transitions. I also tend to agree that the problem seems relevant to a transition between infinite and spotlights. We must have thought a lot of similar things, cos the very light set I'd been playing with when I was attempting to discover more was the Creed Bark at the Moon light! Anyway it's 3.30 am in UK now, and I'm probably ready to try a few other light switches! I'll certainly test your ideas sometime tomorrow and I'll report my findings.