All states have traffic laws that limit the amount of window tint on motor vehicles—often by specifying the amount of visible light transmission (VLT) that is required. VLT is the amount of light that is transmitted through the window and into the vehicle. For example, a 70%VLT means that 70% of light will pass through the window and 30% will be reflected. Thus, a lower VLT indicates a darker film or tint.

Another term to know is visual light reflection (VLR)—which is the opposite of VLT. VLR is the amount of solar energy that is reflected off the glass and away from the inside of the vehicle.

In most states tickets or citations for illegal window tint are known as fix-it tickets and the ticket or citation will indicate that it is a correctable violation of traffic laws. For example, if you fix the window tint problem within the required period, pay a small fine, and get the signature of an authorized person (a local police officer) the court may dismiss the ticket.

But if you fail to fix the window tint problem within the required period you must pay the fine for the violation and you may be issued another ticket that will be part of your driving record. And if you fail to pay the ticket or appear in court on the hearing date the court may issue a warrant for your arrest.

Window tint laws vary from state to state and some states have exemptions for certain vehicles such as limousines and recognize medical exemptions when the driver has a written statement from a licensed medical doctor, ophthalmologist, or optometrist.

In New Hampshire, window tint laws are regulated under RSA 266:58-a, which specifies the amount of light that must pass through car windows to ensure visibility and safety. The state requires a minimum Visible Light Transmission (VLT) of 35% for the front side windows and a VLT of 35% for the rear side and back windows. The windshield may have a non-reflective tint on the top 6 inches. New Hampshire does not allow any reflective or mirrored tinting. Medical exemptions are available for individuals who require a lower VLT due to medical conditions; they must carry documentation from a licensed physician. Violations of window tint regulations are considered 'fix-it' tickets, meaning that if the issue is corrected within a specified period, and verified by an authorized person such as a local police officer, the ticket may be dismissed after paying a small fine. Failure to correct the violation can result in a fine and potential additional tickets, which may affect the driver's record. Non-compliance with paying fines or appearing in court can lead to a warrant for arrest.