acrylic tank lighting issues
 

Hi everyone,
I was wondering about lighting on acrylic tanks. The acrylic tanks that are sold by my lfs have tops that are part of the tank but have about a 12inch by 8 inch hole in the middle of the top.
For the lighting I wanted to go with a 175 ice cap and iwasaki 15K but the reflectors for SE bulbs are larger than the 12 by 8 inch hole and I was wondering what would happen to the par if the light had to travel through about 1/4 inch thick acrylic to get to the water. It wouldn't have to go through the acrylic all the way around only where the 12 by 8 inch hole wasn't cut out.

sry if that doens't make sense.

so also i was thinking about some 150 DE bulbs because their reflectors are more compact and would fit nicely over the hole so the light would never have to pass through the acrylic. It is only a 20 gallon tank and I only really want to keep zoos and LPS and easy SPS

as an afterthought is there any danger of the acrylic melting???