Minimum internally reflected component for vertical windows -- Algorithm 2.42

The minimum internally reflected component Dim will normally be located near the wall farthest from the window. Hopkinson(1) provides graphs showing how the ratio of the minimum to the average value of internally reflected component can be linked to the average reflectance of the room, . These graphs have been used to generate a polynomial function.

Input

Average IRC

Area-weighted average reflectance of ceiling, floor and walls, including windows,

Area-weighted average reflectance of floor, rf

Equation

This equation is based on the assumption that the ceiling has a reflectance of 0.7, and for a range of from 0.3 to 0.6 and a range of rf from 0.15 to 0.4. For other values of ceiling reflectance BRE(2) provide a table of conversion factors to apply to Di :

Ceiling reflectance	Conversion factor
0.4	0.7
0.5	0.8
0.6	0.9
0.7	1.0
0.8	1.1

Source

Sharples(3)

References

1. Hopkinson R G, Petherbridge P and Longmore J Daylighting (London: Heinemann) (1966)

2. Building Research Establishment Estimating daylight in buildings: Part 2 BRE Digest 310 Building Research Establishment (1986)

3. Sharples S, Page J K and Souster C G Modelling the daylight levels produced in rectangular, side-lit rooms by vertical windows containing clear or body-tinted glazing Department of Building Science, University of Sheffield (1981)