Fig 1. Residential application.                           FIG 2. Interior view of  window with LGS.             FIG 3. Application on a relocatable.


WHAT IT DOES :  The concept of the LGS arose from the need to shade windows without reducing natural lighting in sub-tropical buildings. A major problem in Australia is radiant heat gain through windows. This is particularly severe for East or South facing windows in the morning (see Fig 4 below) and West or South facing windows in the afternoon and can also be a problem for North facing windows in winter. The most effective conventional remedy for radiant heat gain is the 45 degree sloping shade (see Fig 5). However this conventional shading severely reduces natural lighting. 




    Fig 4. The problem of radiant heat gain.                            Fig 5. The conventional solution

To circumvent this problem the LGS was designed as a sloping shade that accepted part of the incident sunlight, diffused that sunlight so that it lost its directional dependence and reflected the diffused light through the shade and onto the ceiling in the room using reflectors based on non-imaging optics. Fig 6 below shows a section through a typical LGS with the path of a few typical rays of the diffused light from the aperture indicated. The lower reflector is a parabola in section and the upper reflector is a plane reflector. It is possible to design the upper and lower reflectors in the shade so that the light emitted into the room occupies a specified angular range. Fig 7 below shows the relative lighting performance of a conventional shade (a LGS with input aperture covered) and an LGS (right hand photo).



Fig 6. Sunlight through a diffusing aperture is reflected through the shade onto the ceiling.    Fig 7. Conventional shade (LHS),  light guiding shade (RHS).

In practical designs (see Fig 1, 2 and 3) the output light is emitted into the building in an angular range from a few degrees above horizontal up to about 70 degrees above horizontal to ensure the window is glare free. However, the design may be continuously varied to provide narrower output emission. As the input light is diffused at the entry aperture the output distribution is independent of the input direction of the sunlight. Therefore the LGS performs much like a conventional luminaire giving an unchanging light distribution within the room. A different, but very desirable, feature of the LGS relative to conventional luminaires is that, as the output light is directed upward, the output aperture appears relatively dark (low glare) when viewed from inside the room.

APPLICATION IN SCHOOLS: see Victorian Schools Lighting Demonstration

HOW IT IS MADE :  see Construction sequence - light guiding shade.

ECONOMIC BENEFITS : see Reduced air conditioning costs

COMMERCIAL :  Australian Patent No. 657749. Commercial partners are sought to manufacture and market this product under license.
This product is currently being assessed as part of Victorian School Lighting Demonstration (Sustainable Energy Authority of Victoria).