The solar factor (total transmittance) of a glass relative to that of 3mm clear float
glass (0.87) and is used as a performance comparison. The lower the shading coefficient
number, the lower the amount of solar heat transmitted. The short wave shading coefficient is
the direct transmittance (T) of the glass as a factor of the solar factor or total transmittance (g or TT) of 3mm clear float glass (T ÷ 0.87). The long wave shading coefficient is the internally
re-radiated energy that the glass has absorbed as a factor of the solar factor (total
transmittance) of 3mm clear float glass. It is determined by subtracting the direct transmittance
from the solar factor (total transmittance) of the subject glass and then dividing by the solar
factor (total transmittance) of 3mm clear float glass (g-T ÷ 0.87).