Visible Light Transmission

How Dark Do You Go? Vehicle Tint and Visible Light Transmission

Ok, you have made the big decision – you want to put tint on the windows of your vehicle.  The next question will invariably be – how dark should I go? In most cases, people choose to use a darker film on the back windows and rear windshield, and a lighter tint on the front driver and passenger side windows.  But how do you decide how “dark” to go?

Of course, the best thing to do is consult one of the professionals at Calgary’s top vehicle tint shop, Tint Tech.  We are ready to help answer any and all of your vehicle tint questions.  For decades we have been providing top-notch service to the Calgary region, and want to make sure that you have be best vehicle tint job possible.  For more information call us at 1-403-968-8468, or be sure to fill out our online contact form.    

Now, let’s dive into the factors you need to consider when deciding how dark to go with your vehicle tint.  

Clarity on the Concept of Visible Light Transmission

Tint films have been standardized by how much light they let through.  That is represented as a percentage. The percent value indicates the amount of light that reaches the other side of the film.  So, for example, a 70 percent film is very light because it lets 70 percent of the exterior light through. By contrast, a 5 percent film is extremely dark because it only permits 5 percent of the exterior light through the film. 

Accordingly, the term Visible Light Transmission, or VLT for short, refers to that percentage.  A 70 percent film is called 70% VLT, and a 5 percent film is called 5% VLT, and so on.  

Know the Laws for Your Region

Each province has different VLT regulations about how much light has to be transmitted through the film for your tint to be legal.  For example, some provinces don’t allow any light-blocking at all, others may require that you have a minimum amount of light let through.  Of those, many will not care how dark the tint is around the back seat and the rear windshield, but will have strict requirements about how light the film must be on the front seat.

Remember “Total” Visible Light Transmission

Many automakers manufacture the windows on their cars with some measure of light-blocking already.  Typically, cars off of the assembly line have 80% VLT windows. You can see this effect if you open your car so that it casts a shadow and look at the light that hits the ground through the window.  The window itself will cast a slight shadow, and the light that passes through it should look a little bit dimmer than the direct sunlight that hits the pavement. You need to take this treatment into account when deciding what level of vehicle tint you select for your car. 

Doing the Math

Assume that your windows come from the manufacturer allowing 80 percent of light through, and you live in a region that requires your front windows to allow a minimum of 70 percent of the light outside to enter your vehicle (70% VLT).  You need to figure out what tint to put on the windows and stay in the correct VLT range. The effect of tint is not additive, so you have to calculate the percentage of the film based on the 80 percent of light the window is letting in, not on the 100 percent of light outside. 

To do that, you need to convert the percentages into decimals.  80 percent is 0.8, so you will multiply any additional tint by 0.8 in order to arrive at the value for total visible light transmission.  In the case above where you need to have at least 70 percent transmission, the darkest film you can put on your windows is 90 percent, because 0.8 multiplied by 0.9 equals 0.72, or 72 percent. 

It is highly unlikely that you will find someone selling an 87.5 percent film, which is what you would need to apply to the window in order to arrive perfectly at 70 percent, so the 90 percent film is your best option.  It is the closest to that threshold without violating the rules of the road. 

If you walk into a shop and ask for a 70 percent film to be applied to your windows, but the windows are already blocking 80 percent, you will end up with a total visible light transmission of 56 percent.  That will be far below the minimum limit required. 

It is easy to calculate this in reverse as well.  If you know the laws on how dark the film is allowed to be on your driver and passenger front windows, then you can calculate the level of tint you can have applied and still meet the threshold.  Say your province allows you to have tint on windows up to 35% VLT. Convert that into a decimal so that you have 0.35, now divide it by the natural percentage the window allows. If you divide 0.35 by 0.8, you end up with 0.4375 or 43.75 percent.

You will need to round up to the nearest percentage ending in 5 or 0, depending on who makes the film and what your auto shop carries in stock.  If you can get a 45 percent film, your total visible light transmission will be 36 percent, just flirting with the legal limit. If the only option available is a 50 percent film, then the total will be 40 percent. 

You Do Not Need to Go Too Dark

Keep in mind that you do not necessarily need a very dark tint film in order to reap the benefit of having tint on your car.  Would a 5% VLT film on all the windows of a black car make for a sleek look? Probably. But it may also be a safety hazard, particularly at night when you rely on headlights from other cars to remain aware of your surroundings.  The laws regarding how much light must reach the interior of your vehicle exist because of the potential dangers of limiting driver visibility too much. 

Modern, high quality automotive tint will block ultraviolet and infrared rays from the sun, which will keep your interior cooler and protect the leather or fabric from sun damage.  That means your AC will not have to work as hard to cool the car down in the summer, and will extend the life of the investment you made in your automobile. 

Talk to the professionals at Tint Tech when deciding on the right VLT for your vehicle tint.  Call us at 1-403-968-8468, or fill out our online contact form

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