Thanks for your message! I have been removing all the leaves that seem to be affected in case it is in fact a pest so it doesn't spread.
I know you mentioned the light was a good idea and I thought so too because in my mind 3 60 W incandescent was not too much light.... But I also came across this online http://www.missouribotanicalgarden....dening%20Help/images/Pests/Scorch223.jpg
which is apparently sunburn and does look like some of my leaves!
As a precaution I've turned the light off for now.
Would applying a mild insecticide - I've heard of diluted water and soap or diluted rubbing alcohol be a good idea - do you know anything about that?
Thanks so much!