What is the difference between
SHGC (Solar Heat Gain Coefficient) and SC (Shading Coefficient)?

The Solar Heat Gain Coefficient (SHGC) is the percent of solar energy incident on the glass that is transferred indoors both directly and indirectly through the glass. The direct gain portion is the solar energy transmittance, while the indirect is the fraction of solar energy incident on the glass that is absorbed and re-radiated or transmitted through convection indoors. For example, 1/8" (3.1 mm) uncoated clear glass has an SHGC of approximately 0.86, of which 0.84 is direct gain (solar transmittance) and 0.02 is indirect gain (convection / re-radiation).

The Shading Coefficient (SC) is a measure of the heat gain through glass from solar radiation. Specifically, the Shading Coefficient is the ratio between the solar heat gain for a particular type of glass and that of double-strength clear glass. A lower Shading Coefficient indicates lower solar heat gain. For reference, 1/8" (3.1 mm) clear glass has a value of 1.00 (SC is an older term being replaced by the SHGC).

In either case, a lower number indicates improved solar control over the 1/8" clear glass baseline. With a long air-conditioning season, it is most important to reduce solar gain and therefore reduce air-conditioning loads.