Rules of the Road

How dark can window tint be on a car?

Tom Newsted of Midwest Tinting in Missouri holds a sample of tinted glass applied to cars. The two on the left exceed 24 percent and would be illegal in Washington state. The two on the right, at 5 percent and 20 percent, would be OK.
Tom Newsted of Midwest Tinting in Missouri holds a sample of tinted glass applied to cars. The two on the left exceed 24 percent and would be illegal in Washington state. The two on the right, at 5 percent and 20 percent, would be OK. The Kansas City Star

QUESTION: How dark can window tint be on a car?

ANSWER: Maybe it’s about the heat. Maybe it’s about the style. Maybe it’s about the privacy. Whatever the reason, many people choose to tint the windows of their cars. Proponents of window tinting point to several benefits; big surprise, I’ll start with safety. Window tint is a thin plastic film that goes on the inside of the glass. In a crash, this film can hold together broken glass that would otherwise fly through the car. By design, auto glass breaks into small chunks that are less likely to cause injury compared with jagged shards of glass from, say, a residential window, so while the tint film may help, it’s not as significant a safety feature as it first seems to be.

Window tint nearly eliminates UV rays, protecting a vehicle’s interior and the occupant’s skin. Untinted windows also reduce some UV rays, but folks at the Skin Cancer Foundation don’t think it’s enough. They advocate window film as one solution to protecting yourself from sun while driving. Note that you don’t need darkened tint to block UV rays; it’s not the color of the film but the material from which it’s made that blocks UV rays.

Tinted windows keep a car interior cooler in hot weather, they reduce glare and they add a little privacy. Some people also feel that tinted windows increase vehicle security; a potential thief is less likely to notice something of value in the car. Personally, I wouldn’t rely on tinting as a security measure. Have you seen the data on vehicle prowls? Instead, don’t leave valuables in a car. I know that’s not specifically a traffic safety topic, so consider it a little bonus tip. And finally, for many drivers, window tinting is about style. On some cars, dark windows just look good.

But at some point dark windows can be too dark. In fact, Washington law specifies exactly how dark a window can be tinted. The answer (in most cases): 24 percent.

But what does that number mean? We can’t talk about window tint and the law without discussing “light transmission.” This is the ratio of the amount of light, expressed in percentages, that is allowed to pass through the glass. A window that has 24 percent light transmission blocks 76 percent of the light that shines on the window. The lower the number, the darker the window.

I borrowed a tint meter and checked a few vehicles. My car, which does not have any added tint, actually has a light transmission measurement of 78 percent. Turns out that all automotive glass reduces light transmission a bit. I checked a few more windows on cars belonging to family members and friends and found light transmission as low as 3 percent. That’s not a typo: 97 percent of the light hitting the window wasn’t making it through.

As you might imagine, there are some safety issues with dark tint. On sunny days, dark tint may not hinder the driver’s visibility much, but in Washington we mostly don’t have sunny days. Clouds, rain and darkness combined with dark window tint make for a hazardous lack of visibility. The owner of that car with 3 percent tint is planning on removing the tint, just for that reason.

It’s not just driver visibility, though. Dark tint also prevents the driver from being seen by other drivers. Especially at intersections, the ability to make eye contact helps clarify intent. You’re probably familiar with the “You go, no, you go” routine that sometimes happens at intersections. I’ve been told by local collision investigators that dark window tinting has been a factor in turning some of those exchanges from an annoying driving moment into a crash.

Finally, let’s clear up a few misconceptions about the tint law in Washington. I mentioned earlier that in most cases the lower limit for window tint is 24 percent. There are a few exceptions, but they’re mostly limited to vehicles for hire, emergency vehicles, trucks, RVs and multipurpose passenger vehicles (vehicles built on truck frames or modified for off-road use). On these vehicles, windows behind the driver can be darker than 24 percent. In no situation can the front windows be less than 24 percent. And, except for the top 6 inches, no tint can be applied to the windshield. That means that, despite what a well-meaning friend or the internet tells you, the rear windows in a typical passenger vehicle can’t be any darker than 24 percent.

Also, using a professional shop doesn’t guarantee that your window tint meets the requirements of the law. I would like to believe that most local business people do their best to adhere to the law, but officers in our community have contacted drivers with tint darker than the law allows, installed by professionals. If you’re considering getting your car tinted, arm yourself with the knowledge of the law so you don’t end up with a $136 ticket for extra-dark window tint.

I’m stating the obvious, but visibility is a key component in safe driving. If you tint your windows, make sure it doesn’t affect the primary purpose of driving: safely arriving at your destination.

Road Rules is a regular column on road laws, safe driving habits and general police practices. Doug Dahl is the Target Zero Manager for the Whatcom County Traffic Safety Task Force. Target Zero is Washington’s vision to reduce traffic fatalities and serious injuries to zero by 2030. For more traffic safety information visit Ask a question.