UV filters do not convert the light they absorb it or block it getting into the car.Well from my physics, I think the UV converts to infra red spectrum when passing through glass otherwise we would all get sun burnt in side the car and truck drivers wouldn't need to wind their windows down... However I think the general principle is correct?
The UV range of light covers a spectrum and something that blocks UV may only block it in part of that spectrum so while modern cars do block some UV light to some degree you can still get sunburnt inside a car with the windows up.
It is UV that damages the colour of things, so if you leave something in a car for several years you'll still find colours fade, the plastics used in cars are designed to not fade under sunlight for long periods, something like a soft toy left on a parcel shelf is not designed to be so resistant to UV and the sun will easily bleach the colours
Yep literally what we're saying, its not all IR though.This is why the car heats up inside - all that extra infra red.
Yes, but as stated in that link this is quite new, Its also more difficult to block the non visible light without any affect on the visible light, far easier to darken the glass and block light from across the whole spectrum.As the link above suggests you can create UV and IR reflecting films that don't actually give any real tint;
Plus many people tend to get windows tinted for the tint and the dark window look. 99.9% of them don't get them tinted for the UV protection. If you're going to pay several hundred for all round tints then most people want to see some difference.
The point is that tinted windows tend to be cooler on a hot bright sunny day because of the extra UV and IR protection they afford.
Science is a bit more nuanced than 'dark thing get hot'