Yeah good point really.
I guess you can only go on feedback from other who have tried it. I think theres a link on gti.co.uk to the topic on the S3 forum. I can find it for you if you want?
I upgraded my bulbs to some 80W ones, so hopefully it should be ok.
They do state that the film still allows 90% of light through, so I look forward to seeing whether thats just clever marketing, or the truth!!