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Meter Math


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There remains to a large degree, a great deal of confusion about automotive film laws and which films are compatible with which cars, in which states and under which circumstances.

If these are issues you are already very familiar with, bear with me. Based upon the continuous flow of questions we get at EWF about this issue, I am creating this post to help make things a little clearer for all of those who are still a little confused by it.

Not a week goes by when we don’t get a call from a dealer(s) asking why their customer got a ticket when they put 35% film on a car and “the law says 35%”.

First: There are two types of laws:

Film Laws: Laws that regulate only the applied film

Net Laws: Laws that regulate the net transmission of glass+film (most common)

You are responsible for knowing what type of law your state has on the books. If you need an up-to-date listing state laws, there is a terrific website called Tintdude that has a list. I suggest you visit that site some day.

Second: There are variables

You are aiming at a moving target, so you have to adjust accordingly. Here are some of the variables you need to take into account:

VLT range of the glass 70% - 84% (generally)

VLT variance on your film +/- 3% per industry guidelines

VLT precision on your meter +/- 3% some meters are worse than this

State Law Tolerances +/- 3% (This will vary from state to state)

Some brief Do’s and Don’t’s:

Do own a meter

Do perform a “test shot” (more on that below)

Do discuss the law with your clients

Do ask your film supplier about all the available VLT’s they offer

Do know about the law enforcement situation – Is it part of annual inspection?

Do strive to become an expert on this topic – your customers are depending on you

Do keep your meter battery fresh and learn how to self calibrate it (if possible).

Do keep a variety of shades on hand so your customer has a choice.

Do NOT put a piece of film into a net (glass+film) meter and rely upon that reading

Do NOT guess. Instead, measure

Do NOT guarantee your customer a legal reading unless you are certain it’s legal

Do NOT hesitate to ask your supplier if you have questions.

How to perform a “test shot”:

To do this, all you need is a meter and a small piece of film (4 inches X 4 inches perhaps). Install the small piece of film onto the window and meter it. Do this before you proceed with the actual installation. Show the reading to the customer and discuss the applicable state law (including any allowable variances). Once you both agree that the VLT range is within your requirements and expectations proceed with the job.

Meter Math:

Get out your calculator. Here we go:

Example #1: What is the expected net range for an applied 42% film?

As discussed above, the VLT range on the glass itself is generally 70%-84%

0.42 X 70 = 29.4%

0.42 X 84 = 35.3%

From this example, we can see that a 42% can meter anywhere between 35.3% and 29.4%. Now factor in the additional variables due to VLT tolerances, meter tolerances, etc and the results can vary by an additional 3%-4%. If you do business in a 35% net law state, take note.

You can adapt this example to suit any film you are considering. Just substitute the 42% (0.42) for another value.

Example #2: What film should I use if my net law requires 35%?

For this example, we will do basically the same calculation (backward).

0.35 / 70 = 50.0%

0.35 / 84 = 41.6%

We can see that if the customer has dark factory tint (70%) then 50% film would be required to hit the 35% net target. If the customer has lighter glass (closer to 84%) then a 42% film can probably be used. The calculation will work both ways. Don’t forget to factor in the other variables and perform the test shot.

I hope this post is helpful. If you have any questions, feel free to contact me at howard@buytint.com


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Edited by EWF
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This is indeed a very helpful and educative post. It was surely a good thing for you to explain the two types of laws. To many this was definitely a new info. Explaining about the do’s and don’ts was just few of the best helps anyone hope for. And it’s good that you also explained how to make the work better. The best way to explain something to someone is to explain the matter with an example.

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