Background of the Invention Some known detector units comprise a lens for focusing signals from a detection footprint into a sensor. Using a lens has some advantages but, but the thick lens material required tends to cause a relatively high absorption loss of the signal being detected. Another problem with lenses is that it is usually necessary for the lens to protrude somewhat from a surrounding housing, which is undesirable for aesthetic reasons. It is therefore desirable to use a reflector, which can reflect signals from a detection footprint into the sensor, with much lower losses. A reflector may, for example, be around 95% efficient. A reflector is especially beneficial in a lighting control system, which needs to have a high sensitivity. Using a reflector may also enable the unit to be more aesthetically pleasing because the reflector tends not to protrude from the detector unit.

It is desirable, particularly in lighting control

systems, to have a detection footprint that closely matches the room or space into which the detector is fitted. For example, if the detector is to be installed in a rectangular room, a circular footprint spanning the room will not cover the corners of the room.

To address this problem, detector units that produce a square detector footprint have been suggested. For example the "Presence Control PRO IR Quattro Impulser" by STEINEL Professional uses a generally angular lens to create a square detection footprint. However, using a lens gives rise to the above-mentioned loss in sensitivity compared to a reflector. Furthermore, angular-shaped lenses are thought to create undesirable aesthetics. Square or rectangular housings (which may be needed to match these angular lenses) are also

difficult to install because they require a square hole to be created rather than simply being able to use a rotating circular cutter to create a circular hole.

An alternative approach is to provide a large enough circular footprint to reach all areas of the room. However, this is wasteful as much of the detection footprint will be on the walls of the room. Such an arrangement may also have poor sensitivity because there may be large blind spots between the active zones in the footprint. Alternatively or additionally, such an arrangement may require a large reflector, resulting in an unduly bulky detector unit.

Another problem is that detector units can sometimes be installed in sub-optimal positions in a room. For example, a detector unit may be designed for operation in the centre of a room, but may need to be installed off-centre due to the presence of other objects, such as HVAC devices. This means the detection footprint will not necessarily fit the room in the correct/originally intended manner.

It is desirable to provide a reflection-based detector unit that overcome or mitigate at least some of the above- mentioned problems.

Summary of the Invention

According to a first aspect of the invention, there is provided a detector unit for a lighting control system, the detector unit comprising: a sensor and

a reflector arranged to reflect signals from a detection footprint into the sensor,

wherein the reflector comprises a plurality of reflective elements, the reflective elements being adjustable such that the shape of the detection footprint of the detector unit may be adjusted.

By providing adjustable reflective elements, the shape of the detection footprint can be tailored to the space in which the detector unit is to be used.

The shape of the detection footprint may be adjustable in various ways : The detector may be arranged such that the reflective elements are adjustable to adjust the size of the detection footprint (i.e. to create a smaller or larger shaped footprint) ; this may enable the detector to zoom in, or out, over a particular area. Zooming in may be beneficial if the detector needs to have a high-resolution in a particular area, such as in proximity to an entrance to a room, and/or it may allow the detector to accommodate various mounting heights. The detector may be arranged such that the reflective elements are adjustable to adjust the outline perimeter of the

detection footprint. For example, the detection footprint may be adjustable such that it is non-circular, such as an angular shape that better matches the shape of a room. The detector may be arranged such that the reflective elements are

adjustable to adjust the layout of active zones within the detection footprint. For example, the centre of the footprint may be asymmetrical to ensure a high resolution in a

particular area, or to compensate for the detector not being centrally installed in a room. The detector may be arranged such that the reflective elements are adjustable to adjust any combination of the above-mentioned aspects of the shape. The reflective elements may be adjustable in any way that achieves the above-mentioned adjustment in shape of the detection footprint. In preferred embodiments of the

invention the tilt of the reflective elements is adjustable to adjust the shape of the footprint. The tilt of each

reflective element may be independently adjustable. Adjusting the tilt of a reflective element may move the active zone of that reflective element (i.e. the zone from which it is arranged to receive a signal and reflect it to the sensor) radially inwardly or outwardly. Each reflector element may be arranged to pivot to/from a tilted position. The tilt of each reflective element may be adjustable from a respective first angle of tilt to a respective second angle of tilt. Each reflective element may be biased towards the first angle of tilt. The first angle of tilt is preferably the angle of tilt required to create a larger detection footprint than the second angle of tilt.

The reflective elements are preferably arranged such that the spacing between each reflective element and the sensor is substantially independent of the tilt of each reflective element (the spacing typically refers to the mean spacing of all points on the reflective element from the centre of the sensor) . For example the spacing between a reflective element and the sensor is preferably the same when the reflective element is at both the first and second angles of tilt. Such an arrangement may enable the reflective elements to be maintained at their focal length from the sensor, independent of their angle of tilt. The reflective elements are

preferably arranged to tilt about a pivot in such a way that achieves this function; the reflective elements may be

arranged to tilt about their centreline, but may also be arranged to tilt to one side of that centreline (or even about one end) if, for example, the reflective element is sufficiently small that the reflective elements is maintained substantially at its focal length from the sensor when tilted about an off-centre pivot.

The plurality of reflective elements may be located equidistant from the sensor. For example, the reflective elements may be arranged in a ring coaxial with the sensor. The focal length of each of the plurality of reflective elements is preferably substantially equal. Such an

arrangement enables the reflector to be relatively easy to manufacture and/or design and may also allow the detector unit to be circular.

In principle, the reflective elements may be adjustable in a variety of different ways, such as via an actuator or via direct manual repositioning. More preferably, the detector unit comprises an adjusting member for adjusting the plurality of reflective elements. The reflective elements may be adjusted in dependence on the relative positions of the adjusting member and the reflective elements. The adjusting member may comprise a contact surface shaped to adjust the reflective elements in dependence on the contact between the contact surface and the reflector. For example, the contact surface may be shaped to adjust the tilt of the reflective elements in dependence on the extent and/or position of, the contact between the contact surface and the reflective

element.

The adjusting member may be moveable from a position remote from the reflective elements, to an adjusting position in which the contact surface has contacted the reflector, thereby adjusting the reflective elements, and more preferably thereby adjusting their tilt. By providing an adjusting member, the user may adjust the reflective elements without needing to touch them directly, thereby reducing the risk of fingerprints or dirt on the reflective elements and/or sensor. The adjusting member may be a ring. The adjusting member may be axially displaceable along the axis of the reflector. The adjusting member may be axially displaceable by virtue of a pure translation, or, for example by a rotation resulting in a translation (such as via screw thread or camming action) .

The magnitude of the adjustment of the reflective elements may be dependent on the magnitude of the axial displacement. The adjusting member may be arranged to adjust all the reflective elements in the same way (for example to adjust their tilt in the same way to zoom the footprint in or out) . The adjusting member may be arranged to adjust the reflective elements in different ways (for example to change the outline perimeter of the footprint or to create an asymmetrical footprint) .

The detector unit may comprise a plurality of adjusting members, each adjusting member being suitable for (for example by virtue of the shape of the contacting surface) creating a different detection footprint. The adjusting members may, for example, be supplied in a package with the other parts of the detector unit give the installer a variety of possible

detection footprints depending on where the detector unit is to be fitted. According to another aspect of the invention, there is provided a package comprising a detector unit as described herein, and a plurality of adjusting members for adjusting the plurality of reflective elements.

The detector unit preferably does not comprise a lens. The reflector is preferably arranged to reflect signals directly from the footprint to the sensor (i.e. without the signals having been focused through a lens) .

According to another aspect of the invention, there is provided a reflector for use as the reflector in the detector units described herein.

According to another aspect of the invention, there is

provided a method of setting up a detector unit in a lighting control system, the detector unit comprising a reflector arranged to reflect signals from a detection footprint into the sensor, the reflector comprising a plurality of reflective elements, wherein the method comprises the step of adjusting the plurality of reflective elements, such that the shape of the detection footprint of the detector unit is adjusted.

According to yet another aspect of the invention there is provided a lighting control system comprising a light and a detector unit as described herein, the light being controlled in dependence on the output from the sensor of the detector unit. The lighting control system may comprise a plurality, and more preferably a multiplicity of lights, the lights being controlled in dependence on the output from the sensor of the detector unit.

According to yet another aspect of the invention there is provided a detector unit comprising:

a sensor and

a reflector arranged to reflect signals from a detection footprint into the sensor,

wherein the reflector comprises a plurality of reflective elements arranged at substantially the same spacing from the sensor, but at least some of the reflective elements being at differing angles of tilt, such that the detection footprint is non-circular .

By providing reflective elements at differing angles of tilt, non-circular detection footprints can be obtained, using a circular arrangement of reflective elements. For example, the plurality of reflective elements are preferably arranged in a ring coaxial with the sensor. This facilitates a

circular detector unit. Furthermore, by arranging the

reflective elements at substantially the same spacing from the sensor, the reflective elements can all focus on the sensor without needing to have the reflective elements with different focal lengths. The reflective elements may all have the same focal length. This may enable the reflector to be relatively easy and inexpensive to manufacture. The detector unit of this aspect of the invention is preferably for a lighting control system.

In some embodiments of the apparatus of this aspect of the invention, the tilt of the reflective elements is fixed. For example, the tilt of the reflective elements of the reflector may be designed to create a specific detection footprint. It will be appreciated that some embodiments are covered by both more than one aspect of the invention

described herein (for example an embodiment in which the reflective elements are substantially the same spacing from the sensor, and at differing angles of tilt, but are also adjustable from those angles of tilt) .

The detection footprint typically comprises a plurality of active zones (each being associated with a corresponding reflective element) interspersed with blind spots. The layout of the active zones corresponding to the plurality of

reflective elements is preferably non-circular.

In accordance with all aspects of the invention, the reflector comprises a plurality of reflective elements. The reflector may comprise a multiplicity of reflective elements. The reflective elements may be identical (e.g. the same shape, reflectivity and focal length) . The reflector may comprise a plurality of concentric rings, each ring comprising a

plurality of reflective members. The concentric rings may be off-set in an axial direction. In embodiments in which the reflective elements are adjustable, the reflective elements may each be pivotably mounted on the reflector such that their tilt can be adjusted. The reflective elements may be

pivotable independently of each other. For example, the reflective elements may be de-coupled from one another. The detector unit may be substantially circular. The detector unit may comprise a housing. The housing may be circular. The housing may be for fitting in a circular opening in a surface. The detector may be installed in the circular opening in a surface, such as a ceiling. The

detector unit may comprise a circular housing, preferably coaxial with the reflector and/or sensor.

The sensor is preferably a passive infrared sensor. Such a sensor is effective in detecting human movement. The passive infrared sensor (often referred to as a PIR sensor) may be for detecting changes in IR within a given area. The passive infrared sensor may be for detecting absolute values of IR (for example a Microelectromechanical systems (MEMS) sensor for detecting IR radiated from humans) . The detector unit is preferably a presence detection unit.

It will be appreciated that any features described with reference to one aspect of the invention are equally

applicable to any other aspect of the invention, and vice versa. For example, features described with reference to a detector unit of one aspect of the invention may be applicable to a detector unit of another aspect of the invention.

Description of the Drawings Various embodiments of the invention will now be

described, by way of example only, with reference to the accompanying schematic drawings of which:

Figure 1 is a perspective view of a reflector and sensor for a known detector unit;

Figure 2a is a plan view of the reflector of Figure 1 ; Figure 2b shows the detection footprint on the reflector of Figure 2a; Figure 3a is a plan view of a reflector in a detector unit according to a first embodiment of the invention also showing a region in close-up;

Figure 3b shows the detection footprint on the reflector of Figure 3a;

Figure 4 is a perspective view from beneath of a

reflector in a detector unit according to a second embodiment of the invention; and

Figure 5 is a perspective view from above of the

reflector in Figure 5, in combination with an adjusting element .

Detailed Description Figures 1, 2a and 2b show parts of a known presence detector unit. Figure 1 shows a reflector 1001 comprising a series of concentric rings 1003 offset in an axial direction A. Each ring 1003 of the reflector has an inner surface formed of integrally moulded reflective facets 1005. Each reflective facet 1005 is arranged to receive infrared

radiation 1013 (shown being radiated from two people in Figure 1) from a respective active zone 1007 in a detection footprint 1009 (see Figure 2b) .

The facets 1005 within each of the rings 1003 share the same angle of tilt (measured as the angle of inclination to the vertical) and have the same focal length. Each facet 1005 is arranged to focus a signal from is respective active zone onto a passive Infrared (PIR) sensor 1011 located above the reflector 1001.

Figure 2b shows the circular detection footprint 1009 of the reflector 1001. The active zones 1007 are in three concentric rings corresponding to the concentric rings 1003 of the reflector 1001. This detector unit of the prior art is often installed in a room having a polygonal floor space. The detector unit is usually installed in the centre of the room to maximise the coverage of the footprint on the floor space. However, there is often no coverage in the corners of the room. This can cause problems, especially for a lighting control system. For example, a person located in the corner (for example having their desk in the corner) may not be detected by the detector unit. This may lead to the lights being switched off when the person is still present in the room. If there is an entrance to the room in an area outside the detection footprint, a person entering the room may not be detected. This may lead to the lights not being switched on until after the person has entered the room.

To address this problem, it is possible to use a detector having a square detection footprint, such as the "Presence Control PRO IR Quattro Impulser" by STEINEL Professional.

However, to achieve the square footprint, it is necessary to use a lens which gives rise to a loss in signal strength.

Furthermore, angular lenses are thought to create undesirable aesthetics and square or rectangular housings (which may be needed to match these lenses) are difficult to install because they require a square hole to be created rather than simply being able to use a rotating circular cutter to create a circular hole.

Figures 3a and 3b show a reflector 1 for use in a

detector unit according to a first embodiment of the

invention. Where appropriate, corresponding reference

numerals have been used to indicate corresponding features in Figures l-2b, but with the omission of the ^λ 10' or ^λ 100' prefix as necessary. The detector unit (now shown) is for a lighting controls system and is capable or controlling lights in a room in dependence on the output of the PIR sensor (not shown) in the detector located above the reflector. The aspects of the detector unit not illustrated (such as the PIR sensor, the housing) are conventional unless indicated

otherwise .

The reflector 1 comprises three concentric, axially offset, rings 3 in the same manner as the prior art of Figures 1 to 2b. However, in contrast to the prior art arrangement, the reflective facets 5 on the outer-most ring 3 are not all at the same angle of tilt.

Several of the facets on the outer-most ring 3 are of uniform tilt, but as shown in Figure 3a, and most visible in the close-up image of the area surrounded by the dotted line, there are also four equally-spaced sets 15 of reflective facets 5 at a different tilt. Each set 15 of facets 5, comprises three facets 5a, 5b. The central facet 5b on each set has a slightly increased tilt and the two facets 5a either side also have an increased tilt (although of less than the central facet 5b) . In this context, the tilt is measured relative to the axial direction of the reflector (which is also vertical in this case) .

The facets 5a-5b are all tilted about their lateral centreline such that the mean spacing between each facet 5 and the sensor remains unchanged. This allows the focal length of the facets 5a-5b to be identical to the focal length of the other facets 5, thereby making the reflector 1 relatively straightforward to manufacture.

By providing selected facets 5a, 5b at differing angles of tilt, the detection footprint 9 of the reflector 1 is non- circular. As shown in Figure 3b, the active zone 7b of the most-tilted facets 5b is moved outward and the active zone 7a of the facets 5a either side are moved outward, to a lesser extent, to create a square detection footprint 9 (for the sake of clarity only some parts of the footprint 9 are labelling in Figure 3b) . This enables the detector unit to be more

effective in polygonal-shaped rooms, or even open-plan rooms where detection footprints of adjacent detection units can tessellate rather than over-lap or have gaps between.

Figures 4 and 5 show a reflector 101 according to a second aspect of the invention. Where appropriate, corresponding reference numerals have been used to indicate corresponding features from the first embodiment, but with the prefix ^λ 1' or ^λ 10' as necessary.

The upper-most rings 103 of the reflector 101 are identical to that in the first embodiment. However, in contrast to the first embodiment, the facets 105 on the lower-most ring 103 are adjustable. Each facet 105 comprises an resilient arm 117 that protrudes inwardly from a support ring 119. The arm 117 meets the back of each facet 105 along the lateral centreline of the facet (see a comparison of Figures 4 and 5 showing the reflector from below and above, and equal portions of the facets being visible) . The arm 117 is formed from a thin web of the material from which the reflector is moulded such that it elastically allows the respective facets to tilt under the action of a force on the facet 105. Since the arm 117 meets the facet 105 along its centreline, the spacing of the facet from the sensor (not shown) is substantially independent of the tilt of each reflective element. This means each facet continues to focus on the sensor (now shown) when tilted or in its default position.

In the configuration shown in Figures 4 and 5, the facets 5 on the lower-most ring all have the same default angle of tilt (i.e. when no outside force is applied to the facets 105) .

However, the tilt can be adjusted via an adjusting member 121 (see Figure 5) . The adjusting member 121 is a plastic ring shaped to form an interference fit between the support ring 119 and the back of each facet 105, and to fit underneath the arms 117 of each facet. The upper surface 123 of the adjusting member 121 comprises a series of protrusions 125a, 125b. When the adjusting member 121 is pressed upwardly into the space between the support ring 119 and the facets 105 (see arrows in Figure 5) , the protrusions 125a, 125b contact the underside of the arm(s) 117 above them, and adjust the angle of tilt of those facets 105. The extent that the tilt is changed is dependent on the magnitude of the axial movement of the adjusting member 121 relative to the reflector. If the adjusting member 121 is inserted such that the remainder of its upper surface 123 just touches the underside of the arms 117, four of the facets 105 will be tilted by virtue of the four largest protrusions 125b, and the two facets 105 either side thereof will be tilted by slightly less. Thus, the detection footprint of the detector unit will be the same shape as that in Figure 3b.

The detector unit of the second embodiment thus has several of the advantages described with reference to the first embodiment. In addition, the second embodiment has the advantage that the detection footprint can be adjusted in various different ways. For example, the detection footprint could be less angular if the adjusting member were inserted to a lesser extent in the axial direction (for example just until the largest protrusions 125b tilted four of the facets) .

Furthermore, differently shaped adjusting elements could be used in order to create different detection footprints. For example, an adjusting element could comprise identical

protrusions along the whole of its upper surface - this would enable the detection footprint to the zoomed out (if inserted from below the reflector), or zoomed in (if inserted from above reflector) . Alternatively the adjusting element could comprise an asymmetric arrangement of protrusions to create an asymmetric detection footprint. The adjustment element is not reflective and can be relatively cheap to manufacture. In the second embodiment of the invention, the detector unit is sold with several

different shapes of adjustment element to give the installer flexibility to create different detection footprints in dependence on where the user intends to install the detection unit .

In the second embodiment of the invention, the adjusting element forms an interference fit in the reflector. In other embodiments of the invention (not shown) the adjusting element may be inserted in other ways such as via a screw thread, or a via a camming action.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. For example, although the illustrated embodiments show only the outer-most ring of the reflector being adjusted, it would be possible to adjust other rings in the reflector in addition, or instead of this ring. Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable

equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present

invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims.