Visible light transmittance is a measure of the amount of visible light that passes through the glazing material of a window, door, or skylight. Visible light transmittance, or simply visible transmittance (VT), is a fraction of the visible spectrum of sunlight (380 to 720 nanometers), weighted by the sensitivity of the human eye, which is transmitted through a window's, door's, or skylight's glazing. A product with a higher VT transmits more visible light. VT is expressed as a number between 0 and 1. 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.

Some tinted glass used to reduce solar heat gain can also reduce the amount of visible light transmitted, which is not good for daylighting. A spectrally selective tinted or coated glazing, however, can help reduce the solar gain while providing as much visible light as clear glass.