If you tinted your windows to make them darker and you did not test them to ensure that they pass state guidelines, you risk having a police officer do it for you somewhere down the road. When an officer does it, it generally results in a stiff fine. If you cannot purchase a tint meter, you can usually take your vehicle to a place that offers tinting services and ask to borrow theirs for a minute.
Roll down your window approximately six inches and locate a portion of the window that is clean and free from scratches.
Place the meter onto the window using the foamed cutout in the meter.
Press down on the meter until the LED comes on. Wait until the meter flashes a number. This is the percentage of light that makes it through the tint.
Compare the number to your local and state regulations to ensure you comply with the law.