While the standard glass used in car windows can block some UV radiation, a car window tint of good quality from a reputable manufacturer —if applied correctly—can help increase protection from ultraviolet radiation. It can also help preserve the interior of your car, including the upholstery, carpeting, and dashboard, which can fade over time by exposure to sunlight. The amount of light that a window tint allows into the interior varies greatly, and affects how well you can see out. Every state has its own regulations and laws pertaining to the level of darkness it allows for automotive window tints. The volume of light that can pass through your window is referred to as variable light transmission, or VLT. Each state has different regulations concerning VLT percentage, so it's a good idea to check local laws concerning what you're allowed to do.
In addition to blocking UVA radiation, a window tint can provide a couple of safety and security benefits. In an accident, automotive window tint film can actually help hold shattered glass in place or reduce the amount of shattered glass. Darkened windows may also hide or obscure articles left in your car, which may deter a thief.