The Solar Heat Gain Coefficient (SHGC) measures how well a window blocks heat from sunlight. SHGC is expressed as a number between 0 and 1, 0 being the least amount of heat gain and 1 being the most, thus the lower a window's solar heat gain coefficient, the less solar heat it transmits. The NFRC notes that SHGC ratings express the performance rating for the entire window, not just the glass -- this means that SHGC ratings also include the ability of a window to absorb the heat from the sun and transmit it (conduct it) through the entire window and into the room. Therefore other aspects of a window such as framing, thermal spacers etc., as well as the glass (such as tinted or reflected), can affect the SHGC rating. Other characteristics that affect the SHGC are the use of spectrally selective glass, and tints or reflective coatings applied in conjunction with low-e coatings that together can dramatically reduce SHGC but may or may not be desirable depending on your climate zone. Heat-Absorbing, tinted window glazing contains special tints that change the color of the glass and are able to absorb a large fraction of the incoming solar radiation through a window, thus reducing the SHGC, visible transmittance (VT) and glare. Tint does not lower a window’s U-factor because some heat continues to pass through tinted windows by conduction and re-radiation.

Tinted glass and its affect on SHGC and VT: Tinted glass can affect VT and SHGC. Gray and bronze tinted windows reduce both light and heat by the same amount. Blue and green tinted glass allow more light to penetrate and slightly reduce heat transfer.