Glass Glossary

Visible Light Transmittance (VLT)

Last Updated: November 23, 2023

Visible Light Transmittance (VLT) is a measure of how much visible light passes through a window or door glass. It is expressed as a percentage, representing the amount of visible light transmitted through the glass relative to the total visible light that hits the surface. A higher VLT percentage means more visible light is transmitted, while a lower VLT percentage means less visible light is transmitted.

Factors Affecting Visible Light Transmittance

  1. Glass Coatings: Cardinal’s LoĒ™ coatings and other surface treatments can reduce the VLT by reflecting some of the visible light.
  2. Tint: Tinted glass can reduce VLT by absorbing or reflecting visible light.
  3. Glass Thickness: Thicker glass can have a slightly lower VLT than thinner glass due to increased absorption and reflection of visible light.

Importance of Visible Light Transmittance for Occupants

Natural Lighting: Glass with high visible transmittance allow more natural light into a building, reducing the need for artificial lighting and improving indoor ambience.

Passive Solar Gains in Cold Climates: By increased passive solar heat gain, some high VLT glass can aid in keeping the house warm in cold climates.

Daylighting: Glass with high visible light is essential for effective daylighting, a building design strategy that optimizes natural light to enhance indoor lighting quality and reduce energy usage.

Visibility: Glass with high visible transmittance provide clear views of the outdoors, enhancing the connection between indoor and outdoor spaces.

Glare Control: Glass coatings with low visible transmittance, like LoĒ³-340 and LoĒ²-240 glass, can help control glare by reducing the amount of visible light transmitted, improving visual comfort in spaces with direct sunlight.