Light pipes

Light pipes or tubes transmit direct sunlight and natural daylight from roof level into the building space below (Fig. 14.5). At roof level an acrylic self-cleaning dome admits light into a highly reflective pipe, which transmits it down to a white translucent dome at ceiling level where the light is diffused into the space below. The mirror-finish aluminium tube can be of any length including offsets, although the quantity of light transmitted is typically reduced by 3% for each metre length and by 8% for each bend.

Standard light pipe diameters range from 200 mm to 600 mm, although larger sizes up to 1000 mm are available for commercial applications. The systems should be free of condensation and not cause winter heat loss or summer solar gain to the building enclosure. Rectangular units, similar in appearance to standard or flush-fitting conservation roof lights are also available, and the ceiling unit can be a square diffuser to integrate into suspended ceiling systems.

A 330 mm diameter system will typically deliver between 100 W from a winter overcast sky to 400 W under full summer sun, for a straight tube not exceeding three metres in length. Such systems can offer energy-saving solutions to existing buildings, and may be considered as one element within a fully-integrated lighting strategy for new-build.

A more sophisticated system combines the functions of both a light pipe and a wind catcher to admit natural daylight and ventilation into internal spaces poorly served by normal external glazing.

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