Directional transmittance of clear glass t -- Algorithm 2.34

a. Transmittance ti of a beam at angle of incidence i

The angle of incidence is the angle between the direction of the beam and the normal to the glass

Input

Angle of incidence, i radians

Equation

Source

Mitalas & Arseneault(1)

a. b. Mean transmittance T of a rectangular opening

Littlefair has adapted the above equation to enable the effect of glazing on sky component to be assessed. For 6mm clear glass a polynomial function was derived which gives an effective glass transmission correction factor T which would be multiplied by the value of sky component calculated for an unglazed opening (algorithms 2.32 & 2.33)

Input

Altitude and azimuth angles a and b as in algorithm 2.32, radians

Equation

Source

Littlefair(2)

References

1. Mitalas G P and Arseneault J G Division of Building Research Computer Program No. 28: Fortran IV program to calculate absorption and transmission of thermal radiation by single and double glazed windows. National Research Council, Ottawa (1968)

2. Littlefair P J Effective glass transmittance under a CIE sky. Lighting Research and Technology 14 (4) 232-235 (1982)