Visible transmittance (VT)
Visible transmittance, or VT, is a number from 0 to 1 that shows how much daylight passes through a window. A higher number is brighter.
VT measures the share of visible light that gets through the whole product, including glass and frame. A high VT means a bright room. A low VT means a darker, tinted look. Gains in energy performance from coatings can come with a lower VT, so the number helps you balance them.
The NFRC lists VT on the window label next to the U-factor and SHGC. A low-E coating with a high VT can block heat and still keep rooms bright. Read our guide to the NFRC label for the full set of ratings, and see SHGC and U-factor for Texas.
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