1.4.2 Visible Light Transmittance
The Visible Transmittance (VT) is an optical property that indicates the amount of visible light transmitted.
VT is expressed as a number between 0 and 1. The higher the VT, the more light is transmitted. This factor needs to be established in conjunction with and under consideration of the Solar Heat Gain Coefficient (SHGC).
Unfortunately, products with high transmittance of visible light are more likely to transmit solar heat, resulting in a higher and unfavorable SHGC. Consequently, targets for VT and SHGC need to be established in conjunction with external conditions, project criteria and program. Consult with the University of Washington's Integrated Design Lab (IDL) for evaluation and advice. Requirements for VT are dependant on external and internal conditions. A factor of >0.7 is recommended for fully-occupied work areas.
Significant cost reductions due to reduced electrical lighting needs.
Maximum use of natural light, minimum use of electrical lighting. Be wary of glare control issues. See 1.4.6, Interior Solar Shading.
The VT-factor is important in the glazing selection, as it’s directly related to the amount of electrical lighting needed to achieve the required illuminance. VT requirements need to be established in conjunction with 1.4.1 Solar Heat Gain Coefficient.
1.4.1 Solar Heat Gain Coefficient