Interactive Spec Tool

Combined VLT Legality Calculator

Standard vehicle glass isn't fully clear. Factory windows block 20% to 25% of ambient light. Use this tool to compute the true net light transmission when pairing aftermarket film with factory glass.

VLT Math & Compliance Evaluator

Select Jurisdictional Limits

Aftermarket Film VLT35% VLT

0% (Blackout)20% (Dark)35% (Medium)70% (Light)100% (Clear)

Base Glass Light Transmission[?]

75% VLT

50% (SUV Factory Rear)75% (Factory Clear)100% (Absolute Clear)

The Physics of Window Tint Layering

Multiplicative Transmission Law

Optics dictates that when placing one semi-transparent filter behind another, the light transmission multiplies. You cannot simply add the percentages.

Net VLT = Aftermarket Film VLT % × (Base Glass VLT % / 100)

The 35% Film Trap

Installing standard 35% film onto a clear-looking factory window with an integrated 75% light transmission:

35% × 0.75 = 26.25% Net VLT

A state trooper's light meter will read 26%, which violates the 30% VLT threshold in states like Indiana.