Tint Over Tint VLT Calculator
Estimated Final VLT: 0%
Understanding Tint Over Tint (Layering VLT)
Visible Light Transmission (VLT) is a measurement of the amount of light that passes through a window. When you apply a new layer of window film over an existing one—or even over factory-tinted glass—the darkness increases exponentially. Many car owners make the mistake of assuming that adding a 35% tint to a window that is already tinted will result in 35% VLT. In reality, it will be much darker.
The Physics of Light Transmission
Calculating the final darkness isn't additive; it is multiplicative. If you have a piece of glass that allows 70% of light through and you add a film that allows 20% of the remaining light through, you must multiply those two percentages together to find the net result.
The Formula: (VLT of Layer 1 × VLT of Layer 2) / 100 = Final VLT %
Practical Example
If you have a truck with factory-smoked rear windows (usually around 20% VLT) and you decide to "match" the front by adding another layer of 20% tint over the back:
- Layer 1 (Factory): 20% (0.20)
- Layer 2 (New Film): 20% (0.20)
- Calculation: 0.20 × 0.20 = 0.04
- Result: 4% Final VLT (Extremely dark/limo tint).
Important Considerations
- Legal Limits: Most states and countries have strict VLT laws (often 35% or 50% for front windows). Layering often drops the VLT below legal limits even if the film you bought is "legal."
- Optical Clarity: Layering multiple films can sometimes cause distortion or a "hazy" effect depending on the quality of the adhesive and the film material.
- Heat Rejection: While layering makes the window darker, it doesn't always double the heat rejection. High-quality single-layer ceramic films often perform better than two layers of cheap dyed film.