Our guide to visible transmittance explores the various components of this window ratings factor.
Visible transmittance or VT is a measure for how much visible-spectrum light enters through a window. The higher the VT value, the more light enters through the window. The lower the VT value, the less light is trasmitted. VT is a lesser explored window rating and with good reason - compared to U-factor, air infiltration and SHGC, visible transmittance is simply not as important for the average homeowner looking to replace their windows.
The ideal VT rating is really the highest visible transmittance you can achieve, while synonymously achieving the best U-factor and SHGC numbers. This is understandably confusing (at least it is to us!) and therefore best left to the professionals. Here are some generic numbers consumers can expect with with various types of window glass. Clear glass will allow 78% to 84% visible-spectrum light through the window. Low-eII glass allows in 72% visible-spectrum light. Laminate glass allows in 79% visible-spectrum light. A bronze tint with a clear glass allows in 48% to 54% visible-spectrum light.
ProVia Aeris Windows » .47 VT
Sunrise Essentials » .56 VT