WO2014170292A1

WO2014170292A1 - Luminaire and control thereof

Info

Publication number: WO2014170292A1
Application number: PCT/EP2014/057562
Authority: WO
Inventors: Michel Cornelis Josephus Marie Vissenberg; Willem Franke Pasveer
Original assignee: Koninklijke Philips N.V.
Priority date: 2013-04-19
Filing date: 2014-04-15
Publication date: 2014-10-23

Abstract

A luminaire provides illumination in a space. The luminaire comprise a daylight sensor mounted to have a sensing field of view in a generally upwards direction. For example, the light sensor can be mounted on an upper surface of the luminaire. The luminaire includes a direct and/or indirect lighting component for providing illumination of the space. The or each lighting component can be controlled based on ambient light levels estimated at least in part on the light sensed by the sensor.

Description

Luminaire and control thereof

FIELD OF THE INVENTION

The present invention relates to luminaires for use in providing illumination in a space, and to controlling illumination in a space by controlling a lighting component of the luminaire.

BACKGROUND

Indoor lighting systems may contain direct lighting (aimed downward towards a desk or other task area) as well as indirect lighting (aimed at the ceiling). Indirect lighting is considered more ergonomic (less glare and a more even distribution of light in the room) but also less energy efficient (more light losses at ceiling and walls). The lighting is provided by lighting components, for example, in the form of one or more lighting element. In order to save energy, the lighting system may contain sensors that detect the presence of people and the presence of daylight. The light may then be dimmed or switched off in case no people are present or when sufficient daylight is available. For direct-indirect lighting systems, the direct beam produces a local lighting effect and the indirect beam a more ambient lighting effect.

At present, daylight sensors are mounted in a space to be illuminated with a downwardly facing field of view. They can be mounted to a ceiling of the space, oriented downwardly. Also, luminaires are known in which a daylight sensor is provided on a lower surface of the luminaire, with a downward facing field of view.

Daylight sensors can be used to regulate the workplace illuminance level of a workplane in the space by controlling the lighting components based on light sensed by the sensor which is taken to represent current lighting levels.

SUMMARY

There are many challenges associated with the location and management of a daylight sensor.

Daylight sensors are sensitive to variation in color (reflectance) of objects that are below the sensor. As a consequence, each sensor needs expert commissioning and calibration during installation. Furthermore, the sensor needs to be recalibrated when the color of furniture, carpet, paint or other objects in the room change.

Daylight sensors are sensitive to reflected sunlight via windows. This limits the applicability of the sensor with respect to mounting height and distance to windows. As the sensor field of view must not have overlap with a window, the field of view needs to be quite limited. This deteriorates the robustness of the sensor with respect to color variations in the interior.

The invention described herein is based on the inventors' observation that the ambient light level in a room is directly related to the luminance level at the ceiling. In the following embodiments, there is described a luminaire with at least one lighting component providing a lighting beam, combined with a light sensor with a field of view in the direction of the ceiling, the sensor controlling a level of the lighting beam, for example, the dimming level. Since the variation of ceiling colors and reflectances is much smaller than the variation for furniture and carpets, the signal from the ceiling is much more robust and may even need no (re)calibration. Also, a direct view on windows is more easily avoided (the robust signal may allow for a more narrow field of view and the luminaire is closer to the ceiling than to the floor). Furthermore, the sensor can be located on the luminaire so that it is not visible to people in the room, which can be a significant design advantage.

According to an aspect of the present invention there is provided a luminaire for use in providing an illumination in a space, the luminaire comprising: a lighting component for providing illumination of the space when the luminaire is mounted in the space; and a light sensor having a sensing field of view in a generally upwards direction when the luminaire is mounted in the space to receive light from a direction generally upwards of the luminaire and connected to control illumination provided by the lighting component based on ambient light levels estimated at least in part on the light sensed by the sensor.

The lighting component can be an indirect lighting component configured to provide illumination in a generally upwards direction, for example, aimed at the ceiling. This is referred to herein as ambient lighting. Alternatively, the lighting component can be a direct lighting component, configured to provide illumination aimed generally downwardly, for example, towards a workplane such as a desk or task area. An indirect lighting component can be mounted in the luminaire with an exit window which faces upwardly when the luminaire is mounted in the space, while a direct lighting component can be mounted with an exit window which faces downwardly when the luminaire is mounted in the space. A luminaire can comprise both an indirect lighting component and a direct lighting component.

The illumination provided by the lighting component can be controlled to provide a certain ambient light level in the space, or to control a workplane illuminance to a certain level. Either or both of the indirect and direct lighting components may be controlled based at least in part on the light sensed by the sensor.

According to another aspect of the present invention, there is provided a lighting system for controlling illumination in a space, the lighting system comprising a luminaire as defined above, and a controller connected to receive from the sensor a light signal representative of light sensed by the sensor and to generate a control signal to the or at least one of the lighting components of the luminaire in dependence on the light signal.

The controller can be embedded in the luminaire itself, that is a common housing can incorporate the lighting component(s), light sensor and controller.

A further aspect of the invention provides a method of controlling illumination in a space, when a luminaire is mounted in the space with a lighting component for providing illumination of the space and a light sensor having a sensing field of view in a generally upwards direction, the method comprising: detecting a light signal from the sensor, the light signal representing light sensed by the sensor; and controlling the illumination delivered by the lighting component of the luminaire based on the light signal to deliver a space illumination above a threshold value.

In order to permit the contribution from the lighting component to be distinguished from a daylight contribution in light sensed by the light sensor, illumination provided by the lighting component can be modulated at a frequency determined by the controller. When the luminaire has an indirect lighting component and a direct lighting component, the illumination provided by each component can be modulated by a different frequency so that their contributions can be distinguished from each other and from daylight.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made by way of example to the

accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram showing an illuminated space;

Fig. 2 is a schematic diagram illustrating a downwardly aimed daylight sensor; and Fig. 3 is a schematic diagram illustrating a luminaire with an upwardly facing sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 illustrates a schematic cross-sectional view of a space 2, e.g. an office, with direct/indirect suspended luminaires 4 and windows 6 that enable daylight to enter the room. The term "direct/indirect" is used herein to denote a luminaire that has an indirect lighting component configured to aim a generally upwardly non-directional illumination, e.g. toward the ceiling 8 for creating ambient lighting, and a direct lighting component configured to direct a more focused light beam towards a target area, such as a workplane 10 (floor, desk, etc.). The luminaires 4 send a flux φΐ down towards the workplane 10 and a flux cp2 up to the ceiling 8. Through the window 6, a flux cpd of daylight enters the room. By reflection Rc off the ceiling, a flux cpc goes down, and by reflection Rw off the workplane, a flux cpw goes up (note that the reflection factors are averages, taking into account reflection losses at ceiling, walls, furniture, floor, angle of incidence, etc.).

The illuminance at the workplane follows from

UF_L<p-_L + UF_c<p_c + UFiawm <p_£

^: >v

Eq 1 where A is the area of the room 2 (or at least the part of the room that is considered here) and the UF values are the utilization factors of the downward beam, the reflected ceiling light, and the daylight. The utilization factors take into account the light losses during transport from source to target and depend on the geometry of the space, the reflection factors of walls etc. and the directionality of the light.

The upward reflected flux of light follows from

<p_w = U_WH_WA . Eq la

Similarly, at the ceiling the illuminance is p UF₂ -^2 + UF_W& _V + υΡ_αΛψ φ._ά

c^~ A Eq 2 and the downward reflected flux follows from φ, = Ε,Έ,Λ . Eq 3

These recursive equations may be solved to give for the workplane illuminance

_ ^UFl <P l + ^ε ^υ^2 ψ 2 + ^et, clown. ¾% + RcUF& tPa

w^~ A (t - R_CUF_CR_WUF_W) _Eq 4

And for the ceiling illuminance

_ R_lvUF₁<p₁ + UF₂ cp₂ + R_wUF_didgm<p_d + UF_d>up(p_d

A(1 - R_CUF_CR_WUF_W) _{Eq 5}

Figure 2 is a schematic diagram illustrating considerations for a down-looking daylight sensor. The sensor is labeled 20 and is considered to be installed on the ceiling in a space 2 with a window 6, similar to that described with reference to Figure 1. The sensor 20 has an approximately cone-shaped field of view denoted by dotted lines 22. The distance of the longitudinal axis of the cone to the window is denoted Y in Figure 2. The distance between the surface to be illuminated and the daylight sensor in a vertical direction is denoted H. Careful consideration needs to be paid to both Y and H to take into account reflectance and sunlight in the space. Daylight sensors are very sensitive to changes in color and reflectance in the field of view 22, because it senses the luminance of a task area instead of the illuminance. In Figure 2, the task area is denoted 10 similarly to Figure 1. A wide field of view averages out the colors and reflectance variations and leads to a more robust sensor. On the other hand, special care should be taken to avoid that the field of view overlaps with a window: otherwise direct reflections of sunlight into the sensor may cause errors. The width of the sensor field of view in a downward facing daylight sensor is a compromise between both constraints.

Moreover, the sensor needs recalibration (in conditions without natural light) whenever the room paint, furniture, wall art or carpet is changed. Taking into account these issues, consider the case in which a conventional daylight sensor is used to regulate the workplane illuminance level. If the sensor is integrated in the luminaire, it looks straight down with a limited cone angle, such that only part of the workplane flux is captured:

S_{! o (p_w — R_WE_WA. Eq 6

This results in a sensor signal S_d proportional to the workplane illuminance Ew. The proportionality constant between sensor signal and workplane illuminance may be determined by a calibration, which can be required each time the environment changes.

In the case where a down-looking daylight sensor is integrated in the ceiling, special care has to be taken that the sensor is not directly illuminated by the indirect beam (in that case, the signal can be interpreted in the same way as above). If the ceiling is quite uniformly lit, the ceiling sensor will always receive light from the indirect beam and the signal will depend on both the workplane illuminance and the indirect beam flux. The contributions of both sources depend strongly on the exact relative positions of the luminaires and the sensor(s). The problem is that this signal is neither an indication of the task illuminance nor an indication of the ambient illuminance, but a mixture of both.

The inventors have observed that the ambient light level in a room is directly related to the luminance level at the ceiling. Moreover, the variation of ceiling colors and reflectances is much smaller than the variation for furniture and carpets. Thus, to take advantage of these observations, according to embodiments of this invention, a daylight sensor 12 is mounted on the suspended or free floor standing luminaire, looking up to the ceiling (see Figure 3).

In this case, the sensor signal S_u is directly proportional to the ceiling flux. S„ <X ψ, = R E A Eq η

Figure 3 illustrates a luminaire 4 with a daylight sensor 12 mounted with a light receiving window 41 in its upper surface 40 with a field of view in a generally upwards direction. The field of view is generally cone-shaped and is denoted by dotted lines 14. The field of view is indicated diagrammatically only and does not denote any particular proportion. The luminaire is shown suspended by a suspension infrastructure 16 from the ceiling 8. The luminaire has an indirect lighting component 18 which can comprise one or more illumination devices mounted with an exit window 43 intended to provide indirect illumination aimed at the ceiling. The luminaire 4 also carries a direct lighting component which can comprise one or more direct lighting device mounted with an exit window 45 configured to direct illumination generally downwardly towards the workplane 10 and mounted on a lower surface 42. In the luminaire the lighting elements and sensor are embedded inside the housing, such that the exit window 43, 45, 41 (where the light exits the lighting element or the light enters the sensor) is in the plane of the housing surface. The light exit/entrance of the elements is at the side of surface 40 and 42, depending on the intended orientation (up or down). In Figure 3, dashed arrows indicate light exiting the lighting elements.

To complete the picture but in a diagrammatic form, a controller 24 is connected to control the luminaire. The controller includes a processing unit 30, executing a computer program to process light signals and output control signals. The controller can be provided in the luminaire itself, or can be provided within the space connected to a plurality of similar luminaires and/or other lighting devices in the space. The controller 24 receives sensor signals S_u from the sensor 12 based on input detected by the sensor 12 within its field of view. The sensor input S_u denotes the light sensed by the sensor - when converted by the sensor it provides a light signal to the controller 24 representing the sensor input. The controller 24 may receive signals from more than one sensor in the space. The controller 24 is then responsible for adjusting the light output of the lighting components 18 and/or 22 based on the detected sensor inputs from the sensor 12 (and possibly from other sensors in the space), for example, by controlling dimming levels. As described more fully herein, an advantage of the orientation of the upwardly facing sensor 12 is that its individual sensor inputs can be distinguished and used to more directly control the direct lighting component by itself, the indirect lighting component by itself or both. The controller generally operates to save energy while guaranteeing a workplane illuminance above a certain threshold value. In the arrangement of Figures 1 and 3, taking the ceiling illuminance as a measure for the ambient light level, the sensor signal gives a direct measure that can be used to control the indirect beam from component 18 (responsible for flux o₂). The advantage of this signal is that the ceiling reflectance is very constant in time and space, which results in a more robust signal that needs less or no calibration.

The upward looking sensor 12 may also be used to regulate the task illuminance at workplane level, according to the following method. The problem to be solved is that the three light source fluxes (direct beam, indirect beam, and daylight) have different contributions to the ceiling illuminance compared to the workplane (or task) illuminance. This is caused by the different directions of the light, which results in different utilization factors and different reflections needed to end up at the ceiling or workplane.

The three contributions may be sensed individually by modulating the direct beam and the indirect beam at distinct frequencies invisible to the human eye. This can be achieved by modulators 26, 28 in the controller 24. Although shown separately from the processing unit 30, they could be implemented by software in the unit 30. The modulating frequency is supplied to the respective lighting component from the controller 24. Thus the sensor input can be subdivided into three distinct signals, a direct light signal S_ui , and indirect light signal S_u2, and a DC signal that represents the ambient (day)light S_ud:

A - R_c TrF_c R_w r!F_w)' Eq 8

Ail-E_CUF_CE_WUF_1VJ

Here, C is a proportionality constant that depends on properties of the sensor (size, viewing angle). By combining these three sub-signals, the workplane illuminance may be estimated according to υΡ₁ψ₁ + Β_ΕυΡ₂φ₂ + UF_Aaown(p_a + R_cUF_a

A (l - R_CUF_CR_WUF_W) q l 1

CR_CR_W C CR_c R_w UF_djdQwn + UF_diUp i.e. each subsignal has a different calibration constant. The three subsignals may be used to dim either the direct beam, or the indirect beam, or both, to save energy while guaranteeing a workplane illuminance above a certain threshold value.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practice in the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should be construed as limiting the scope.

Claims

CLAIMS:

1. A luminaire (4) for use in providing an illumination in a space, the luminaire comprising:

a lighting component (18, 22) for providing illumination of the space when the luminaire is mounted in the space; and

a light sensor (12) located on the luminaire (4) and having a sensing field of view in a generally upwards direction when the luminaire (4) is mounted in the space to receive light from a direction generally upwards of the luminaire and connected to control illumination provided by the lighting component based on ambient light levels estimated at least in part on the light sensed by the sensor (12).

2. A luminaire according to claim 1, wherein the lighting component is an indirect lighting component (18) for providing illumination in a generally upwards direction towards a ceiling of the space.

3. A luminaire according to claim 2, wherein the indirect lighting component (18) is mounted in the luminaire such that an exit window faces upwardly when the luminaire is mounted in the space.

4. A luminaire according to claim 1, wherein the lighting component is a direct lighting component (22) configured to direct illumination generally downwardly towards a workplane.

5. A luminaire according to claim 4, wherein the direct lighting component is mounted in the luminaire such that an exit window (45) faces generally downwardly when the luminaire is mounted in the space.

6. A luminaire according to claim 2 or 4, wherein the light sensor (12) is mounted in the luminaire with a light entry window (41)which faces upwardly when the luminaire is mounted in the space.

7. A luminaire according to claim 2 or 3, which comprises a further direct lighting component (22) configured to provide illumination in a generally downwards direction towards a workplane, wherein the light sensor is connected to control illumination provided by one or both of the indirect and direct lighting component.

8. A lighting system for controlling illumination in a space, the lighting system comprising a luminaire (4) according to claim 1 or 7, and a controller (24) connected to receive from the sensor a light signal representative of light sensed by the sensor and to generate a control signal to the or at least one of the lighting components of the luminaire in dependence on the light signal.

9. A lighting system according to claim 8, wherein the controller is housed by a housing of the luminaire.

10. A lighting system according to claim 8 or 9, comprising a modulator (26) for modulating illumination from the lighting component such that the contribution of illumination from that lighting component can be determined in the light signal.

11. A lighting system according to claim 10 when comprising a luminaire according to claim 7, comprising a second modulator (28), wherein the first modulator is configured to modulate illumination from the direct lighting component and the second modulator is configured to modulate illumination from the indirect lighting component at a frequency different from that utilized by the first modulator.

12. A lighting system according to claim 1, wherein the luminaire is constructed as a free standing or suspendible structure.

13. A method of controlling illumination in a space, when a luminaire (4) is mounted in the space with a lighting component for providing illumination of the space and a light sensor (12) having a sensing field of view in a generally upwards direction, the method comprising:

detecting a light signal S_u from the sensor, the light signal representing light sensed by the sensor; and controlling the illumination delivered by the lighting component of the luminaire based on the light signal to deliver a space illumination above a threshold value.

14. A method according to claim 13, wherein the workspace illumination is measured at a workplane.

15. A method according to claim 13 or 14, wherein the illumination provided by the lighting component is modulated with a frequency allowing the component of that illumination to be distinguished from a daylight component in the light signal.

16. A method according to claim 13, wherein the lighting component of the luminaire is an indirect lighting component (22) intended to provide illumination directed generally upwardly towards a ceiling of the space, and wherein the luminaire comprises a direct lighting component (18) configured to generate illumination in a generally downwards direction towards a workplane, and wherein the method comprises:

modulating illumination provided by the indirect lighting component at a first frequency;

modulating the illumination provided by the direct lighting component at a second frequency;

determining from the light signal respective contributions (S_ui , S_u2) from the direct and indirect illumination based on the modulating frequencies; and

controlling the illumination delivered by the client and/or indirect lighting component based on the determined contributions.