I had professionals put this on our windows, Kathy - I found them in the yellow pages under `window film'. There were 3 levels of reduction-of- light film to choose from, I chose the middle one, but wish I'd chosen the top level in hindsight. I had trouble geting permission (I should not have asked, as others didn't) from the management board of our condo building to have it put on and thought I shouldn't use the darker one because of that. I had to get a letter from my neurologist about light sensitivity to get the management board to agree.
We live in an extremely sunny apartment (afternoon and evening sun) with 3 balconies. The windows that we had done cost about $200 Canadian each and I understand it costs about 2/3rds of that to remove the film. We have to use non-commercial window cleaner on those windows (just vinegar and water will do the job). It certainly helps with everyday sun but I still have to close the verticals in the late-afternoon summer sun.
Hope this helps.
June in Toronto (beb/meige)