ADVANCED DAYLIGHTING SYSTEMS IN NORMAN PARK STATE SCHOOL, BRISBANE.
A daylighting system admits natural light to the interior of buildings. The basic forms are windows and skylights – simple transparent apertures in the walls and roofs of buildings that allow direct transfer of radiant energy to the interior. Advanced daylighting systems utilise the radiant energy more effectively by distributing the radiation more efficiently in the interior and by making the input more even over the day. Norman Park State School has two advanced daylighting systems providing natural lighting – light channelling panels in the windows and angle selective skylights in the roof.
Light channelling panels (channel panels).
Channel panels redirect nearly all incident radiation into an upwards direction onto the ceiling of the room. This is achieved by forming tiny reflective channels within a clear plastic panel by laser cutting, (Fig 1).
Fig 1. View of one corner of a channel panel showing reflective laser cuts forming small light channels within a clear panel. Height of each channel is 3.2 mm. Thickness of the panel is 12 mm.
The passage of light through a single light channel (see below) illustrates that high angle light is redirected deep over the ceiling of a room. Low elevation light is also redirected to the ceiling but not so deeply into the room.
With the channel panel almost all incident sunlight is redirected upwards onto the ceiling. Fig 2 illustrates this effect in Norman Park School. The channel panel in the left hand clerestory window redirects light to the ceiling whereas the right hand conventional clerestory allows sunlight to fall on the floor of the room. The clerestory windows in this school are the first application of channel panel anywhere.
Fig 2. Left hand clerestory window with channel panel redirects sunlight to the ceiling. Note the external shade over the lower part of the window.
Light redirected to the ceiling more efficiently illuminates the room, providing more light for the same amount of heat, and distributes the light more effectively. Consider the diagram below showing a room illuminated by a conventional clear clerestory (left) and a clerestory with channel panel (right).
When light passes through the clear clerestory and falls on the blue carpet most of the light energy is absorbed and converted (wastefully) into heat. Some blue light is reflected but this reflected light does not fall directly on work surfaces and tends to give the walls and ceiling of the room a bluish tint that is rather gloomy. Conversely, light through the channel panel clerestory is redirected to the white, highly reflecting ceiling. Most of this light is reflected as white light and falls efficiently on work surfaces. Thus for the same radiant input through the window much more natural lighting of work surfaces is achieved.
The larger of the two sizes of channel panel used in Norman Park State School are 1.7 m wide and 0.25 m high, see Fig 3. In sunlight a panel this size admits natural light equivalent to 38,000 lumens. After reflection from the ceiling about 27,000 lumens are available for natural illumination of work surfaces. This is equivalent to the lighting available from ten 40 W fluorescent tubes.
Fig 3. A channel panel (1.7 m x 0.25 m) as used in the larger clerestory windows at Norman Park State School.
Angle selective and light spreading skylights.
Angle selective skylights are designed to collect more low elevation light and less high elevation light than conventional skylights. This is achieved by including a pyramid of light redirecting panels (laser cut panels) in the skylight. In laser cut panels each laser cut made in a panel becomes a tiny and near perfect mirror that redirects some of the light passing through the panel. The effect is illustrated below. At one angle of incidence all light is redirected.
If laser cut panels are placed at the input aperture of a skylight in pyramid or triangular form the effect is to admit low elevation light and reject high elevation light.
This is important in climates such as Brisbane as it levels out the input through skylights over the day and greatly reduces the possibility of overheating the building interior near noon in summer.
Most of the light from a skylight is directed downward into the room so that areas directly below the skylight get a lot of light (and heat) while areas to the side are not well illuminated. This problem with skylights can be overcome by adding an inverted pyramid or triangle of laser cut panels to the output aperture of the skylight to form a “light spreading skylight”. Fig 4 shows the angle selective pyramid at the top and the light spreading pyramid at the bottom of one of the dual effect angle selective skylights in Norman Park State School. Fig 6 shows an internal view of one of the classrooms illuminated by one of the dual effect skylights installed in the school.
Fig 4. Looking up through the light spreading pyramid at the ceiling, through the skylight well, to the angle selective pyramid at the roof aperture of the skylight.
Fig 5. Interior view of a classroom illuminated with a “dual effect” skylight showing the light-spreading pyramid redirecting light over the flared ceiling on each side of the skylight. Illumination obtained under overcast sky conditions. Note that channel panels had not yet been installed in the clerestory windows in the background.
This school installation is the first application of a dual-effect angle-selective skylight anywhere.
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