I have acrylic tops on all my tanks (lexan, plexiglass all the same) and I have no issue with the light getting thru. I have to keep it clean, once every two weeks or so I pull them off a scrub them. Only thing to watch for is to be sure to use a soft cloth as they do scratch fairly easy.
Also, over time I find they start to sag a bit so I just flip them over. I run a sump so I don't have any cutouts for HOB
filter etc. My tank is a 90 gal
so the acrylic is 18" x 24" approx. I used 3/16" thick.
You could just as easily get a piece of glass cut but with acrylic it is easier to modify if you need to. Basic tools are all that is needed.