Visible Transmittance (VT) measures how much light, visible to the human eye, comes through the window. The solar spectrum is made up of ultraviolet (UV) light, visible light, and infrared (IR) light. VT is expressed as a number between 0 and 1 and the higher the VT the more visible light that’s transmitted. The VT you need for a window, door, or skylight should be determined by your home's daylighting requirements and/or whether you need to reduce interior glare in a space. Through the use of spectrally selective glass, and usually in conjunction with low-e coatings on the interior surface of the pane, windows can block or re-radiate infrared energy from the sun, thus reducing solar heat gain, while maintaining a high level of transmission of visible light. Daylighting can save 30%-60% in energy usage via reduced use of artificial light.

Tinted glass and its affect on SHGC and VT: Tinted glass can affect VT and SHGC. Gray and bronze tinted windows reduce both light and heat by the same amount. Blue and green tinted glass allow more light to penetrate and slightly reduce heat transfer.