VLT is the percentage of visible light that gets through the film. Low number = dark film. Film multiplies with the glass's own tint, VLT says nothing about heat, and every state sets its own darkness limits — check yours.
The number, in one sentence
VLT stands for visible light transmission — the share of visible light that gets through. A film marked 35% lets about 35% of visible light pass and blocks the other 65%. That's the whole definition. Everything else is consequences.
The part everyone gets backwards
Lower number, darker film. It feels wrong at first — we expect bigger to mean more tint. It's the opposite: the number counts the light that survives, not the darkness added. So 5% is the famous near-black "limo tint," 35% is a medium shade you can still see into, and 70% is barely-there film that mostly works on heat while looking almost clear.
Glass already has a number
Here's the twist pros never forget: car glass isn't 100% clear to begin with. Factory glass typically lets through around 70–80% of light by itself, and many SUVs come with rear glass already darkened at the factory. Film multiplies with glass. A 35% film on 75% glass doesn't give you 35% — it gives you about 26% total. When a customer says "I want 35," a good tinter hears a question, not a number: 35 on the film, or 35 on the window?
Dark is not the same as cool
Remember the three jobs from Lesson 1: light, heat, UV. VLT only measures the first one. An old-style dark dyed film can have a low VLT and still let lots of heat through, while a light modern ceramic film can block heat like a wall. VLT tells you how it will look. It doesn't tell you how it will feel. Never sell — or choose — on VLT alone.
About the law — the honest short version
Every state sets its own rules for how dark tint may be, and the limits differ window by window: windshields are restricted most, front side windows next, and rear windows often allowed darker. The number that matters in law is usually expressed as a maximum darkness — the darkest a window is allowed to test. Rules change, and they are enforced with a meter at the roadside. So the only safe habit is the pro habit: check your own state's current limits before choosing a shade — every state page in this site's tint law section is a starting point, and your state's own published statute is the final word.
Keep Going
Shrinking, Squeegees & Slip — the skills that put any shade on curved glass
Talking to Your First Customers — how to explain shades without a single confusing word