Tinted windows are designed to reject the thermal rays that make sunlight increase temperature. By blocking the rays that create heat while letting the ones that create natural light, it acts as a filter that prevents your vehicle's interior (and you) from heating up without blocking the illuminating features of the sun's rays.
Fun fact: Some of the newer vehicles already have some form of window tint as a part of its factory finish.
Benefits of tinted windows
• Reduced glare
• Reduced interior heat
• Reduced UV radiation
• Increased security
• Interior design preservation
Tinted windows can reduce up to 70% of interior heat and reduce up to 99% of the sun's harmful UV-A and UV-B rays. UV rays are actually harmful enough that it's capable of damaging the interior of your vehicle, causing leather and vinyl surfaces to fade and crack, eventually hurting your resale value. Tinted windows can also deter strangers from looking into your vehicle while making you a safer driver by reducing glare and eye fatigue. Another "hidden" benefit of an automotive window tint film is that it can actually help hold shattered glass in place or reduce the amount of shattered glass. Not to say that it will completely prevent it from shattering, it just has the chance of holding the pieces together.
While getting your vehicle's windows tinted isn't illegal, the legality does vary from state to state and window to window. The common allowable limits are 50% for the driver and passenger side's window, while it's only 35% for the rear and back windows. A great example of this limit is the limit on windshield. While you generally can not tint an entire windshield, a bar that runs across the top may be allowed, depending on the lenght.
DIY Tinted windows
Contact a professional
While it's possible to do it yourself because it can save you time and money, it could possibly end up doing the opposite. You think it'll save you time until you realize you have to clean your work space, ensuring there's little to no dust that can get in the way. You think it'll save you money until you make a mistake of cutting the film too short or ripping it apart and now you need a new one. Truthfully, an experienced professional can do a better job while saving you time and money by making sure the tint is legal, helping you avoid a costly citation.