Here we use tabulated spectral values of transmissivity to compute the total transmissivity of regular glass and of “Low E” glass.  We do this calculation for both solar (short wavelength) and terrestrial (long wavelength) radiation.

 

We perform the required integration using Simpson’s 1/3 Rule.   We check those values with results using tabulated blackbody radiation functions in conjunction with a simple “boxcar” approximation of the actual curves seen above.    This “mini-project” appears on the last sheet of an Excel workbook with details in a separate document.