In 1998 Paul Littlefair of the BRE wrote a seminal paper on this subject, listing as its aims: to improve the distribution of daylight in a space and to control direct sunlight.
Of the various methods none can be said to have achieved a universal application, but each has a specific use and is worthy of mention.
Mirrors. There are many ways in which the interaction of light or sunlight with a mirrored surface can be used for reflection. From the use of a large hand-held mirror to throw light into the dark recesses of a renaissance church for the delight of visitors, to the fixed mirrored louvres which may be related to vertical windows, installed to direct light upwards to a ceiling; alternatively there are those which, when related to glazed openings in a roof, can project light downwards to the interior (see Case Study of the Central United Methodist Church in Wisconsin pp. 142-143). These tend to be specialist solutions requiring the mirror to be controlled by a motorized tracking system or heliostat . . . not for general application.
Prismatic glazing. The principle is to use methods of refraction of light, rather than reflection. Whilst this method can be applied to vertical windows, they are perhaps more successful when associated with systems of rooflight, a good example being Richard Rogers' redevelopment of Billingsgate fish market to a modern computer centre (see Lighting Historic Buildings, p. 64) where sunlight is refracted away from the occupants to eliminate glare, whilst allowing daylight to the space below. As these have only a limited application they are expensive.
Light shelves. It is possible by means of comparatively inexpensive building construction, to provide light shelves. These have already been mentioned in terms of solar shading, but they are useful also to provide a view window below the light shelf, with the light above reflected to the ceiling to redistribute daylight further into the room. It must be recognized that light shelves do not increase the daylight factors in a room, but they alter the distribution, assisting in getting light further towards the back of the room so that uniformity is improved. Light shelves are relatively cheap to install, and are less subject to damage than those used externally, but do require cleaning on a regular basis.
Section illustrating the passage of light pipes through a roof to provide daylight to atop floor room
Light pipes. Of all the methods of innovative daylighting, the light pipe has had the most universal application. It is basically a method of rooflighting, which by means of association with reflective tubes, directs the light to a lower level. Whilst it can be employed to direct light through several floors, this has the disadvantage of locating the pipes through the upper floors, taking up useful floor space.
Light-pipe installations can be associated with a means of ventilation, and also with sources of artificial light which take over after dark or when the daylight outside is insufficient, using a light control system. A particularly useful application has been in domestic buildings, where a light pipe can be directed to an area in the property, such as an upstairs landing, which otherwise might receive no daylight.
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