Dunno about your glass question, but I have never heard of anyone having glass break because of "heat stress". How else can you explain that I live in Arizona where it gets to be 120 degrees in the summer and I've never had my glass in my car or home break because of the sun? :)
That is why my question generated. Certain types of glass, ie tempered glass can with stand heat, others can't. I have no idea what sump glass would of been made of.
But anyway, I am looking at replacing that light with one recommended, and perhaps try and fit the MH light into the tank some how (the exact light is a MH flood light).