Visible Transmittance
Visible transmittance (VT) is the fraction of visible light that passes through a window — daylight, not heat. VT ranges 0 to 1, with most clear double-pane low-e windows landing around 0.50-0.60 and triple-pane Passive House windows at 0.40-0.50. Lower VT means a darker-tinted glass; higher VT means more daylight in the room. VT is independent of SHGC, even though both involve solar radiation — VT is about light, SHGC is about heat.