AU2004100676A4

AU2004100676A4 - Roof lighting sytem

Info

Publication number: AU2004100676A4
Application number: AU2004100676A
Authority: AU
Inventors: Ian Robert Edmonds
Original assignee: IAN EDMONDS
Current assignee: Edmonds Maria Anna Theresia
Priority date: 2004-08-18
Filing date: 2004-08-18
Publication date: 2004-09-09
Anticipated expiration: 2012-08-18

Description

Roof lighting system Background.

As shown in section in Fig 1 a conventional form of roof light comprises a cylindrical light pipe 1 made from reflective material extending from the roof 2 to the ceiling 3 of a room below. The roof aperture of the light pipe is usually protected by a clear plastic dome 4 that is fixed to a collar encircling the light pipe and may have apertures for ventilation. The ceiling aperture of the light pipe is usually fitted with a light diffuser This conventional form of roof light is ineffective in accepting and transmitting low elevation light. As shown in Fig 2 low elevation light ray 6 makes at least 10 reflections in traversing the light pipe. If the reflecting surface of the light pipe is polished aluminium of reflectivity 0.85 the transmission of light ray 6 is 0.85 raised to the power of 10, that is 0.196. Thus the transmittance is less than 20% for low elevation light.

Thus this conventional form of roof light performs very poorly during the first three hours of morning and during the last three hours of the afternoon. This is the time during the day when most residents are at home and require natural light.

This problem can be alleviated, as shown in Fig 3, by including a metallic reflector 7 at the aperture of the light pipe. As shown the reflector accepts low angle light between ray 6 and ray 8 and reflects this light down the light pipe at a small angle to the axis of the light pipe so that the transmittance is high. However a metallic reflector blocks low elevation light incident on the other side of the light pipe as illustrated for light ray 9 in Fig 3. Thus the metallic reflector increases transmittance from one side but reduces it from the other side.

This problem can be overcome by using transparent light redirecting panels which redirect light by reflection at interfaces formed inside the material of the panel. A method for producing light redirecting panels by laser cutting is described by Edmonds in US 4,989,952. Such panels are called laser cut panels (LCP). The use of laser cut panels 10 to redirect low elevation light from both sides down a light pipe is illustrated in Fig 4.

It is difficult to find simple, mechanically strong and economical ways to install light redirecting systems such as laser cut panels at the aperture of light pipes. One method is to form rigid three dimensional structures of laser cut panel material and locate these structures on the roof aperture of a light pipe. Methods of producing rigid three dimensional structures of laser cut panel material are outlined in an application by Edmonds AU 2003204904. However such methods are suited to producing small structural systems to fit small diameter light pipes typically 250 mm diameter light pipes. Using such methods to produce systems to fit light pipes of diameter 400 mm or greater is limited by the size of acrylic sheet available and the fact that using these methods to produce large systems results in a high wastage of raw acrylic material. Thus the objective of this innovation is to describe a method for producing a roof light that utilises laser cut light redirecting material in the form of single panels, one or more of which may be very simply installed and firmly located at the roof aperture of a conventional roof lighting system of the type illustrated in Fig 1 without making any modification to the conventional roof lighting system and without requiring any additional form of fixing means other than that inherent in the structure of the conventional roof lighting system. A further objective is to describe a method by which a conventional roof lighting system can be very simply and economically converted to a roof lighting system with greatly increased light transmittance of early morning, late afternoon and winter sunlight.

Summary of the innovation.

The innovation describes a roof lighting system comprising a cylindrical light pipe, a clear dome and one or more panels of light redirecting material. Each panel has two symmetrical angled slots cut in the lower edge of the panel that allow the panels to be located on the upper edge of the light in the desired orientation to redirect low elevation light down the light pipe. The panels are firmly located in position by two contacts at the edge of the light pipe and one or more contacts against the surface of the dome.

Brief description of the drawings.

Fig 1 shows a conventional roof lighting system Fig 2 shows the ineffective transmission of low angle light through a conventional roof lighting system.

Fig 3 shows that a metallic reflector can reflect light down a light pipe but only from one side.

Fig 4 shows that laser cut light redirecting panels can redirect light from both sides down a light pipe.

Fig 5 shows the conventional collar and dome of a conventional roof light.

Fig 6 shows the shape of light redirecting panel suited to location on the cylindrical collar of a light pipe Fig 7 shows a laser cut panel of this innovation located between the collar of a light pipe and the clear dome.

Fig 8 shows two laser cut panels located between the collar of a light pipe and the clear dome.

Fig 9 shows a plan view of a pyramid arrangement of four panels on a light pipe.

Fig 10 shows the distribution of laser cuts over a panel of this innovation.

Fig 11 shows a section through the roof lighting system of this innovation with low elevation light being redirected down the light pipe.

Detailed description of the innovation.

Fig 5 shows the collar assembly that comprises the roof aperture of a conventional cylindrical roof lighting system. It comprises a metal collar 11, a support plate 12, which may contain vents and a clear dome 4 which is fixed to the support plate 12. The diameter of the collar is usually 400 mm or greater. The cylindrical light pipe fits inside the collar and extends from the collar to the ceiling below.

Panels of light redirecting material cut to the general shape shown in Fig 6 can be located around the upper edge of the collar. Symmetrical angled slots 13 are cut in the base edge of panel 10. The angle and width of the slots determines the slope at which the panel will lie when located on the cylindrical collar. For example vertical slots of narrow width will locate the panel in vertical orientation on the collar. For effective light redirection the angle between the plane of the panel and the plane of the aperture of the light pipe should be about 60 degrees. Or equivalently the axis in the plane of the panel and perpendicular to the base of the panel should make an acute angle with the central axis of the light pipe of about degrees. For a panel at this slope the inner sides of the slots are cut at about 30 degrees to the base and the outer sides cut at about 50 degrees.

However the angle, width and depth of the slots cut in the base depend on many factors, and vary according to the diameter of the collar, the height of the collar, the number of panels to be located about the collar, the thickness of the panels and the slope of the panels. A panel 10 located on the collar 11 and with the base edge meeting support plate 12 is shown in Fig 7.

The shape of the panel 10 above the base edge should be cut so that points, for example 14 and 15 in Fig 6 and Fig 7 locate against the surface of the dome when it is fixed on support collar 12.

Fig 8 shows two light redirecting panels 10 located on collar 11. Fig 9 shows a plan view looking down the axis of the light pipe showing four light redirecting panels 10 located to form a truncated pyramid arrangement on the collar of the light pipe. Such an arrangement would redirect low elevation light from all directions down the light pipe.

Fig 10 shows that laser cuts 16 are made through the maximum area of the panel 10 in order to maximise light acceptance and redirection.

Typically the laser cuts are made through acrylic panels of thickness 6 mm at a spacing of about 3.5 mm and at an angle of about 12 degrees to the normal to the panel.

Fig 11 shows a section through the roof lighting system of this innovation showing how angled laser cuts 16 in the panels 10 redirect low elevation light 9 down the light pipe at a small angle to the axis of the light pipe.