The shading coefficient is defined as:

• A. The ratio of solar heat gain through the glass from radiation.
• B. The ratio of heat loss through the glass.
• C. The daylight transmittance of the glazing.
• D. The U-factor of the glazing.

Answer: (A)

Shading coefficient measures how much solar heat enters through glazing from sunlight, expressed as a ratio to a standard reference glass. It quantifies solar heat gain through the glass under the same conditions as that reference, so it reflects the effect of radiation on interior heat. It is not about heat loss (that’s the U-factor), not about daylight transmittance, and not about heat transfer in general. A higher shading coefficient means more solar heat gain, while shading devices and coatings lower it.