Light shelves

Light shelves have been in use for some time and serve the dual purpose of providing shade and reflected light. Sunlight is reflected from the upper surface of the light shelf into the room interior and particularly onto the ceiling where it provides additional diffuse light thus helping to provide uniform illumination. Under conditions of an overcast sky, light shelves cannot increase the lighting level. They operate most effectively in sunlight. In this context ceilings are usually designed to be higher than normal for best operation (Figure 14.3).

Some degree of control is possible by modifying the angle of the light shelf; either internally or externally or in combination. Problems with low angle winter sunlight penetration can give rise to glare. Difficulties can be experience in cleaning the light shelves, especially the external type.

Earlier, Portcullis House illustrated this feature with a level of sophistication involving a corrugated reflective surface to maximise high altitude reflection whilst rejecting low altitude short wave solar radiation. This almost doubles the daylight levels in north facing rooms.

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