If you have shopped for tint, you have seen numbers like 5%, 20%, and 35%. That figure is VLT — visible light transmission — the percentage of visible light that passes through the glass and film together. A lower VLT means darker glass and less light reaching the cabin (and your eyes). It is the single most important number in the entire tint world: it decides what is legal, what is dark enough to help, and what your installer actually applies.
Master this one percentage and everything else — state limits, medical exemptions, film marketing — suddenly makes sense. Here is how to read it like a pro.
The one thing to remember
Quick rule: lower VLT = darker tint. A 5% film blocks about 95% of visible light; a 50% film blocks about half. The number is what gets through, not what is blocked.
How to Read VLT Percentages
Here is how the common percentages translate into what you actually see, and how people typically use them:
| VLT % | What it looks like | Common use |
|---|---|---|
| 70%+ | Nearly clear | Factory glass, UV-only films |
| 50% | Light, barely-there tint | Glare reduction, factory look |
| 35% | Noticeable but see-through | Popular legal front-window choice |
| 20% | Dark; hard to see in | Privacy; many rear windows |
| 5% | "Limo" — near-opaque | Maximum darkness / privacy |
A useful mental model: 35% still lets you make eye contact through the glass in daylight; 20% turns occupants into silhouettes; 5% behaves like a one-way mirror in bright sun. Most light-sensitive drivers find meaningful relief somewhere in the 20–50% range, depending on their condition and their state’s rules.
Film VLT vs. Installed VLT
Here is the nuance that trips people up: a film’s advertised VLT and your installed VLT can differ, because your factory glass already filters some light. A 20% film on glass that is itself 80% VLT yields a combined reading closer to 16%. That is why enforcement uses a meter on the finished window — the only number that matters legally is the one the meter reads on your actual glass, not the spec printed on the box.
Always confirm with your installer whether a quoted VLT is the film rating or the expected installed reading on your vehicle. The difference can be the line between legal and not.
What the Law Cares About
Each state sets a minimum legal VLT for each window position — and the limits are often different for each one:
- ✓ Windshield — usually only a non-reflective strip along the top (often the "AS-1" line) is allowed.
- ✓ Front side windows — the most tightly regulated, commonly 30–50% in many states.
- ✓ Rear side windows — frequently allowed darker, sometimes any darkness.
- ✓ Rear window — often unrestricted if you have working side mirrors, but not always.
Run darker than the limit without authorization and you risk a citation. Your exact numbers are in the 50-state exemption guide.
- 4
- Window positions states regulate
- Lower = darker
- How VLT scales
- Metered
- How limits are enforced
How a Medical Exemption Changes the Math
A medical exemption legally lets you go below your state’s standard VLT limit when a licensed provider documents that darker tint is necessary — for example, to manage photophobia or protect against UV-related skin cancer recurrence. The provider supports the lowest VLT that is clinically justified; what counts as "darkest legal" then shifts for you specifically.
In practice that means two drivers in the same state can legally run very different VLTs: one capped at the standard 35% front limit, the other approved for a darker film because of a documented condition. The exemption does not erase the rules — it rewrites the number that applies to you.
Choosing the Right Number
Darker is not automatically better. Going too low can hurt night visibility for some drivers, so the right medical VLT balances symptom relief against safe sightlines. A good rule of thumb: choose the lightest tint that still controls your symptoms. Our guide on window tint and night driving explains the tradeoff, and best window tint for light sensitivity covers condition-specific choices.
Common VLT Myths
- "Darker means more UV protection." False — UV rejection is a separate spec; a light film can still block ~99% of UV.
- "The film-box VLT is what police read." False — they meter the installed glass, which is darker than the film alone.
- "All 20% films look the same." Not quite — color, clarity, and reflectivity vary by film type and quality.
- "A medical exemption means any darkness is fine." No — your provider documents a specific, justified VLT.
VLT Is Not the Whole Story
Two films at the same VLT can perform very differently on UV and heat. UV rejection and infrared (IR) heat rejection are separate specs — a tint can be relatively light yet still block about 99% of UV and a large share of radiant heat. If protection rather than darkness is your real goal, the film type matters as much as the percentage; compare options in ceramic vs. dyed window tint.
VLT tells you how dark the glass is. It does not tell you how well the film protects you — which is why two "20%" films can be worlds apart.
Frequently Asked Questions
Does a lower VLT percentage mean darker tint?
Is the film VLT the same as my window VLT?
What VLT can I get with a medical exemption?
What is the most popular legal tint percentage?
Does tint darkness affect UV protection?
Can I measure my own tint’s VLT?
References & Further Reading
This article draws on the following authoritative sources. All links go to the primary publisher — none are affiliate links. Last reviewed May 2026.
- International Window Film Association — Understanding VLT — International Window Film Association
- American Academy of Ophthalmology — Light Sensitivity — American Academy of Ophthalmology
- American Academy of Ophthalmology — UV Protection and Sunglasses — American Academy of Ophthalmology
- CDC — UV Radiation and Your Health — Centers for Disease Control and Prevention
This article is educational and is not medical or legal advice. MyEyeRx is a consultation-booking and referral service; clinical evaluations and any exemption documentation are performed by independent, U.S.-licensed physicians and optometrists. Tint laws vary by state and change over time — always confirm current rules with your state and a licensed provider.