Average internally reflected component for rooflights -- Algorithm 2.43
The average internally reflected component for a horizontal rooflight can be
found using an approach similar to that used for vertical windows.
- Glazed area of the rooflight aperture (with a curved glazed surface, this
is the aperture area not the area of curved surface), Aw m2
- Total area of ceiling, floor and walls, including glazing, A m2
- Area-weighted average reflectance of ceiling, floor and walls, including
- Average daylight factor on inside face of rooflight aperture,
- Angle subtended of the visible sky, measured from a point in the plane of
the internal surface at the centre of the window opening, q' degrees (as
- Diffuse light transmittance of glazing, including effects of dirt,
- Where the rooflight recess forms a deep cavity, as with skirted dome-type
lights, reflection within the cavity is significant. The computation then
requires 2 stages: calculation of the mean daylight factor at the base of the
cavity, the ceiling plane of the room; then calculation of the IRC for the
room. Alternatively, tabulated values of may be used, as in BRE Digest 310
(given there the symbol K).
- BRE Digest 310(1) .
- 1. Building Research Establishment Estimating daylight in buildings:
Part 2 BRE Digest 310 Building Research Establishment (1986)
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