Say “20% tint” to one person and “35% tint” to another, and you will often get two different guesses about which is darker. The number confuses plenty of people, yet reading it correctly matters for VLT, Visible Light Transmission and Perth compliance before any film goes near a window. As the mobile window tinting specialists working across the Perth metro area, we spend a lot of time helping customers understand this figure first, so the finished result matches what they actually pictured.
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What VLT Actually Means
VLT stands for Visible Light Transmission. In plain terms, it is the amount of light that passes through the glazing. That single word, through, is the key to the whole concept.
The percentage measures how much light gets let through, not how much gets blocked. A film rated at 35% VLT allows roughly 35 per cent of visible light to pass. The remaining share is reflected or absorbed before it reaches the inside.
Once you fix that idea in your head, the rest of the number starts to make sense.
Reading Tint Percentages Correctly
Because VLT describes light let through, a lower number means a darker film and a higher number means a lighter one. This feels backwards to many people, which is exactly why the confusion happens.
- A 70% film lets most light through, so it looks very light and subtle.
- A 35% film sits in the middle, noticeably tinted but still clear to see through.
- A 20% film lets far less light through, so it reads as distinctly dark.
- A 5% film blocks almost all visible light and appears nearly black.
So when two figures are compared, the smaller one is always the darker option. Keep that rule in mind and you will never mix up a “20” with a “35” again.
VLT of the Glass Versus VLT of the Film
Here is a point many people miss: the film’s rating is not the same as the final result on the window. Glazing itself can already affect how much light passes through before any film is applied.
That means the figure printed on a roll of film describes the film on its own. Once it goes onto a particular pane, the combined result can read differently from the film’s standalone number. In practice, what matters is the total light transmission of the finished window, not just the film’s rating in isolation.
This is why a measured reading on the actual glass gives a truer picture than the box label alone.
How VLT Is Checked in Practice
In the real world, VLT is confirmed by taking a reading through the completed window rather than trusting the film’s label. A reading through the finished glass captures everything at once: the glazing and the film working together.
When people talk about a window being “compliant,” they generally mean that this measured reading sits within the range that applies to that type of window. The important takeaway is that compliance is judged on the actual glass in front of you, not on a theoretical film rating. Specific allowances vary, so it is always worth confirming the measured figure rather than assuming.
Balancing Darkness and Usability
A very low VLT has real appeal. It cuts glare, reduces heat coming through the glass, and adds privacy. But there is a trade-off, and it is worth understanding before you commit.
Government guidance on glazing notes that a low VLT can reduce heat gain, yet if it goes too low it makes rooms too dark and pushes up lighting energy costs. The same logic applies to vehicles and homes alike: push the number too far down and you force more artificial light just to see comfortably.
Reading the percentage correctly is what protects that balance. You want enough darkness for comfort and heat control, without sacrificing the visibility and natural light that make a space liveable. This matters even more in bright local conditions, where the pull toward the darkest option is strong.
Why Perth Owners Should Confirm the VLT First
Before settling on a film, it pays to match your expectations to an actual number. If you want privacy and heat control, decide what level of darkness delivers that without leaving an interior gloomy at night.
Those conditions differ depending on where you are, something we touched on when comparing coastal and inland Perth environments and how they shape tinting choices. Confirming the VLT in advance means fewer surprises and a result that feels right every day, not just on the forecourt.
Once the meaning and measurement of the percentage are clear, the obvious follow-up is how dark each part of a vehicle is actually permitted to be, since the allowed light transmission is not identical for every window. That brings us to the way different windows on a car are treated differently under the rules that apply in WA, and why the front, sides and rear are not held to the same standard.