NZ200982A - Fluorescent tube task light with two outward and downward parallel masking surfaces minimizing direct and indirect reflection - Google Patents

Description

200982 Priority Date(s): Complete Specification Filed: Jb.-.f?.

Class: .j.OSJ Av.

Publication Date: ... ]98& .... P.O. Journal, No: NEW ZEALAND PATENTS ACT, 1953 SSg 16 JUNI982 X&JEtVEO COMPLETE SPECIFICATION - TASK LIGHT We CEMAC MODULAR INDUSTRIES LIMITED, a New Zealand company, of 66 Waione Street, Petone, Wellington, New Zealand hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : — No: Date: This invention relates to luminaires and in particular to an office 'task light" for providing light to a specific work surface.

For a number of years it has been customary for new buildings, particularly office buildings, to be provided with lighting of such intensity throughout that additional localised lighting for work stations is unnecessary. However, the use of ceiling lighting to provide such high light levels is grossly extragavant in energy consumption since such light levels are unnecessary outside defined work stations or work zones. To enable persons to safely and comfortably move around a working space the ambient level of light need be far less than that required at work stations.

As the cost of electricity for lighting and for operating air conditioning equipment to remove waste heat from lighting continues to increase a new lighting philosophy has emerged. That is, where fixed lighting within a building is minimised or eliminated. The user provides localised lighting or task lights for work stations, and also ambient lighting if none is already installed. This philosophy has dove-tailed with the increasing use of open plan offices where lighting is associated with the open plan partitions and fittings rather than the building structure. An example of such an open plan office system incorporating both ambient lights and task lights is the Westinghouse ASD Open Office System.

To further increase lighting efficiency there is a need 200962 to provide task lights of higher efficiency than has' been attained to date. Additionally for many work stations there is a need for a task light which is capable of evenly lighting a surface to one side of the light location.

It is therefore an object of the present invention to provide a luminaire which will meet the aforementioned need or which at least provide a useful choice over other available luminaires.

Accordingly the invention may broadly be said to consist in a task light which can provide substantially uniform illuminance over a work surface which can be located below it and extending to one side of it comprising: at least one fluorescent tube, a reflector system which directs light from said tube or tubes downwardly and to one side relative to the tube, and masking surfaces extending beyond the periphery of the reflector system which, define the width of the beam of light emitted from the j±ask liqht to minimise direct and indirect glare by means of the masking surfaces preventing light from the tube / and reflector system directly reaching the eyes of persons using the vrark sufrace and minimising light reaching the eyes of persons using the work surface indirectly by reflection off the work surface;, said masking surfaces including two or more substantially parallel surfaces parallel to said fluorescent tube extending outwardly and downwardly from said fluorescent tube such that light reaching the work surface must pass therebetween.

The preferred form of the present invention will now be described with reference to the accompanying drawing which shows a diagramatic transverse section through the luminaire of the present invention.

In addition to the low energy requirements already mentioned, luminaires for use with open plan office systems ' ■A - 3 - OCTS985S 2 009B should meet the following criteria: (i) be of an overall size suitable for attachment to the underside of a shelf or cabinet whether the shelf is parallel to or at right angles to the work surface to be lit, (ii) light output must be sufficient at the mid-zone of the work surface when the luminaire is mounted at reasonable shelf heights over one end of the work surface, and (iii) the light produced must provide good contrast rendering without appreciable glare either direct or reflected.

In determining the light level required to be produced by a task light on a work surface account must be taken of the light level supplied by ambient light. A reasonable minimum for ambient lighting is about 200 lux. A reasonable design light level on a normal work surface is 400 lux and accordingly a task luminaire should be able to provide a light level of 200 lux to the work surface. For a long work surface which can only be conveniently lit from the ends it may be necessary to provide two end mounted task lights to provide sufficient light level over the full length of the work surface.

In order to render direct glare negligible to persons sitting near the task light it is to be expected that the configuration of the task light will be at least in part determined by this criterion. The requirement means that there be total cut-off to lamps and flashed areas of any reflectors from normal head heights.

Referring now to the drawing, the main components of the luminaire shown will be briefly itemised. A fluorescent 200982 tube 1 is mounted in the upper rear portion of a lamp housing defined in the transverse section by the plane surfaces AB, BC, C'D, DE, EF. Light produced by the fluorescent tube 1 is emitted through the sideways displaced opening AF. The work surface to be lit is located vertically below point B and extends horizontally (to the right in the drawing) well beyond a point vertically below point F.

In order to provide a suitable light level from a very low power fluorescent tube at a work surface displaced laterally from that tube it is necessary to provide a reflector system. In the preferred form of the invention shown in the drawing the primary reflector system comprises surfaces 2, 3 and 4. These are formed from mirrored acrylic plastic sheet and sufficient directivity may be achieved by a nu-nimum of the three facets shown. The facets are in cros sect ion tangential to a substantially parabolic curve which extends behind and above the tube. These may be glued or clipped to the end plates of the luminaire (one of which is designated 7). It should be appreciated that a suitable - reflector could be provided as a single curved unit or if flat surfaces are used the number of surfaces could be greater than the three shown.

Masking surfaces 5 and 6 determine the degree of direct and indirect glare. It will be appreciated glare is a particular problem with side lights. As can be seen from' the drawing surface 5 is well below the height of the fluorescent tube 1 and reflectors to screen them from direct view from persons sitting in the proximity of the luminaire. Surface 6 reduces the problem of indirect glare by i- 2 0098 preventing direct light from the tube and reflectors reaching a zone of work, surface below it which could reflect this light into the eyes of a person sitting at the work surface. However, the provision of such a low cut-off with surface 6 produces a sharply defined shadow on the work surface and to ameliorate this surface 5 is provided with medium level reflectivity to direct sufficient light immediately below the luminaire to minimise the shadowline which might otherwise be produced. A suitable reflective coating is provided by the use of matt white paint.

Surface 6 and the interior of the luminaire end plates 7 are readily visible by persons sitting near the work surface and to minimise direct glare from these surfaces they are treated with a matt black coating.

In some applications of the luminaire described the transverse dimension between end plates 7 may be required to be such that a compatible physically sized fluorescent tube may provide insufficient light level to the work surface to be lit by the luminaire. In such a circumstance a second fluorescent tube may be provided with its own reflector system to increase the light level produced by the luminaire. In the drawing a second such system is shown identical to the first and built integrally with the first to form a double unit. Thus fluorescent tube 11 and surfaces 12, 13, 14, 15 and 16 correspond identically to tube 1 and surfaces 2, 3, 4, 5, and 6 already described.

With the double system shown in the drawing it may be more easy to obtain a luminaire which is square in plan if 00982 the transverse dimension is restricted to be in the order of 300 to 400mm so as to fit under a typically sized shelf. Such a square unit may have advantages when used in common open plan office configurations. For example, where the luminaire is mounted under a unit such as a shelf or cabinet and the work surface runs lengthwise under that unit the luminaire can be oriented so that the fluorescent tubes are at right angles to the lengthwise directions of unit and work surface. On the other hand where the lengthwise directions of a unit and work surface intersect at right angles at one end of the work surface then the luminaire can be rotated through 90° so that the fluorescent tubes are running parallel with the lengthwise direction of the unit. With realistic overall physical sizes of luminaires according to the present design, luminaires which are greatly out of square in plan may not be able to permit such a 90 rotation.

In one preferred size of the present luminaire incorporating the double system shown in the drawing the luminaire is approximately 300mm square in plan and uses two 8 watt fluorescent tubes. With such a luminaire mounted 3 70mm above a work surface approximately 1800mm long and 7 50mm wide an illuminance of 200 lux can generally be provided over the task area within the work surface which with an ambient light illuminance of 200 lux is quite satisfactory. The illuminance provided by task lighting may be doubled if required by mounting a luminaire as described at each end of the work surface in opposed fashion.

Claims (8)

WHAT WE CLAIM IS: 2.00982 t

1. A task light which can provide substantially uniform illuminance over a work surface which can be located below it and extending to one side of it comprising: at least one fluorescent tube, a reflector system which directs light from said tube or tubes downwardly and to one side relative to the tube and masking surfaces extending beyond the periphery of the reflector system which define the width of the beam of light emitted from the task light and minimise direct and indirect gl are, the masking surfaces preventing light from the tube and reflector system directly reaching the eyes of persons using the work surface and minimising light reaching the eyes of persons using the work surface indirectly by reflection off the work surface, said masking surfaces including two or more substantially parallel surfaces extending parallel to said fluorescent tube and extending outwardly and downwardly from said reflector system such that light reaching the work surface must pass therebetween.

2. A task light according to claim 1 wherein there are two parallel spaced apart fluorescent tubes and said reflector system comprises two reflector sub-assemblies, each mounted behind a respective fluorescent tube.

3. A task light according to claim 2 wherein there are six masking surfaces, two surfaces masking the ends of both said tubes and being perpendicular to said tubes, two upper surfaces which each mask a respective tube against direct glare and two lower surfaces which each mask a respective tube against indirect glare, E?v>\ / cthe latter four surfaces extending parallel to said tubes. V -N'TO

4' 1h A task light according to claim 3 wherein the four masking t -o - 200982 surfaces parallel to said tubes are each parallel to each oth er.

5. A task light according to claim 4 wherein one respective side of six planar members form the six masking surfaces and the planar members together with a top cover fixed thereto constitute a casing of the task light.

6. A task light according to claim 4 wherein the upper masking surface relative to the first tube and the lower masking surface relative to the second tube are the two sides of a common planar member.

7. A task light according to any one of claims 2 to 6 wherein each reflector sub-assembly comprises three planar reflectors which in cross-section are tangential to a curve which extends behind and above said tube.

8. A task light which can provide substantially uniform illuminance over a proximate work surface which can be located below it and extending one side of it substantially as hereinbefore described with reference to the accompanying drawing. <=0 jMa/their authorised Ajewti^ A. J. PARK & SON.