Optical feedback system

FIELD OF THE INVENTION

The present invention pertains to the field of lighting and in particular to an optical feedback system for a luminaire including light-emitting elements.

BACKGROUND

Advances in the development and improvements of the luminous flux of light- emitting devices such as solid-state semiconductor and organic light-emitting diodes (LEDs) have made these devices suitable for use in general illumination applications, including architectural, entertainment, and roadway lighting. Light-emitting diodes are becoming increasingly competitive with light sources such as incandescent, fluorescent, and high- intensity discharge lamps.

One of the central problems to be addressed with LED technology is the variation of device characteristics, such as light output, dominant wavelength and forward voltage. These parameters can fluctuate due to variations in manufacturing conditions and can also be strongly temperature dependent. Whereas the change in parameters with temperature can be determined, the temperature dependence is typically not uniform for each color. To complicate this situation even further, the device characteristics can also change during the lifecycle of LEDs.

In order to control the light output of an LED based luminaire, the total delivered light typically should be monitored accurately. This requires placing light sensors, for example photodiodes or other forms of light detection devices, in such a manner that a known fraction of the light intensity from each light source intercepts one or more of the sensors. In addition, the amount of sensed light should be sufficient to essentially ensure satisfactory signal-to-noise ratio for the operation of a feedback loop in order to control the functionality of the light sources.

For example, United States Patent No. 6,741,351 discloses a method for positioning one or more red, green, or blue photodiodes for detection of light from an LED luminaire comprising an array of red, green and blue LEDs. An equal fraction of light is sampled from each LED in order for the total light output to be monitored accurately, which

is performed using a reflecting element to redirect light from the LEDs to the photodiodes. Individual colors are measured sequentially by pulsing the LEDs and then using particular photodiodes or color filters in combination with photodiodes, for detecting the light from the LEDs. United States Patent No. 6,803,732 describes an LED array having a plurality of LED chains, each having at least one LED and being connected in parallel. The LED array has at least one output for feeding back radiation generated to a power supply unit. At least one reference LED chain is connected in parallel with the LED chains and a photosensitive component is provided, the photosensitive component detecting the radiation emitted by the reference LED chain. The photosensitive component generates a measurement signal in a manner dependent on the radiation generated by the reference LED chain, wherein this signal can serve to provide feedback to the power supply unit.

United States Patent No. 6,689,999 describes a light emitting diode lighting apparatus that includes a power supply for providing a fixed direct current; a light emitting diode head for emitting light; and a controller for adjusting the level of said light output on said head and compensating for efficiency altering effects of said light in said power head, whereby said controller receives signals for optical feedback stabilization, temperature compensation, and detection of short term current changes to adjust said light and efficiency. United States Patent No.5,783, 909 describes a circuit for maintaining the luminous intensity of a light emitting diode (LED) comprising at least one LED for producing an luminous intensity; a sensor for sensing a condition proportional to the luminous intensity of the LED and for producing a luminous intensity signal; a power supply electrically connected to the LED for supplying pulses of electrical energy to the LED; and wherein the power supply includes a switching device responsive to the luminous intensity signal for adjusting the electrical energy supplied by the pulses per unit of time to adjust the average of the current passing through the LED to maintain the luminous intensity of the LED at a predetermined level. In one instance, the sensor includes means for sensing changes in the operating temperature of the LED. In a second instance, the sensor includes means for sensing changes in luminous output of the LED. The electrical energy supplied by the pulses per unit of time are adjusted by any one of varying the frequency, varying the width of the pulses, a combination of frequency and width, or adjusting the phase of the pulses within an AC sinusoidal wave form.

United States Patent No. 5,471,052 describes a sensor system for recognition of the color of an object using two or more primary light sources of different characteristic

chromaticity and one primary photosensitive element which receives light from the light sources after it has reflected off the target object and a secondary photosensitive element which receives light from the light sources prior to reflection off of the target. The color of the light of the primary light sources is determined along with the light reflected from the object. Adequate processing of the two signals yields the color of the object. Alternatively, the reflected light can be used in a feedback loop to control the primary light sources. Light emitted from the light sources is carried to the object using a fibre-optic bundle which may be split off and directed to a secondary receiver that measures the light and uses the signal to regulate the output of the light sources. The secondary receiver may also be placed in a light box with the light sources.

United States Patent No. 5,838,451 describes an apparatus with solid-state emitters and detectors for measuring the spectral intensity distribution of light reflected from or transmitted through objects. Similarly, in this invention optics are used to redirect light before it is incident upon the detectors. In addition, the embodiments of this invention employ a temperature based feedback loop for controlling the light emitted by the solid-state emitters which can require elaborate calibration of the system components.

United States Patent No. 6,127,783 describes a white light luminaire with LEDs in each of the colors red, green, and blue. An optical fibre collects a portion of the light emitted by the LEDs and directs it to a photodiode that provides input for a feedback control circuit that controls the electric current through the LEDs. The control circuit turns off the LEDs for the colors not being measured in a sequence of time pulses and compares the measured light output for each color to a desired output.

While there are many prior art methods and systems for collecting illumination generated by light sources such as LEDs, the design of these prior art systems can be complicated and can have inaccurate detected signals. Therefore there is a need for a new optical feedback system for collecting and detecting light from light sources for enabling a desired level of control of the light sources.

This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical feedback system. In accordance with an aspect of the present invention, there is provided an optical feedback system for a luminaire comprising a plurality of light-emitting elements configured to emit light, the optical feedback system comprising: a primary mixing chamber optically coupled to the plurality of light-emitting elements, said primary mixing chamber configured to mix the light emitted by the plurality of light-emitting elements; a light collection device optically coupled to the primary mixing chamber and configured to extract a sample of the light, said light collection device including a light entry aperture positioned relative to the primary mixing chamber such that the sample of the light has a desired level of homogeneity; and a light sensing device optically coupled to the light collection device, said light sensing device configured to detect the sample of the light guided thereto by the light collection device.

In an embodiment of the present invention, an object of the present invention is to provide an optical feedback system for a luminaire having a plurality of light-emitting elements, wherein the optical feedback system is configured to mitigate the non-homogeneity of the radiation patterns of the light-emitting elements on the detection of the characteristics of the light emitted by the luminaire.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 illustrates a perspective view of a luminaire including an optical feedback system according to one embodiment of the present invention.

Figure 2 illustrates a top plan view of the luminaire illustrated in Figure 1.

Figure 3 schematically illustrates locations of a light-emitting element and the light collection device, for determination of homogeneity of light-emitting element contribution to the sampled light, in accordance with one embodiment of the present invention.

Figure 4 illustrates a correlation between the level of equality of light-emitting element contribution to the sampled light relative to the vertical location of the light entry aperture which is optically coupled to the primary mixing chamber, in accordance with one embodiment of the present invention.

Figure 5 illustrates a plurality of light-emitting elements configured and oriented in a configuration according to one embodiment of the present invention, wherein the plurality of light-emitting elements are configured in a radial rotational configuration.

Figure 6 illustrates a plurality of light-emitting elements configured and oriented in a configuration according to one embodiment of the present invention, wherein the plurality of light-emitting elements are configured in a free rotational configuration.

Figure 7 illustrates a correlation between the level of equality of light-emitting element contribution to the sampled light relative to the vertical location of the light entry aperture which is optically coupled to the primary mixing chamber, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Definitions

The term "light-emitting element" (LEE) is used to define a device that emits radiation in a region or combination of regions of the electromagnetic spectrum for example, the visible region, infrared and/or ultraviolet region, when activated by applying a potential difference across it or passing a current through it, for example. Therefore a light-emitting element can have monochromatic, quasi-monochromatic, polychromatic or broadband spectral emission characteristics. Examples of light-emitting elements include semiconductor, organic, or polymer/polymeric light-emitting diodes, optically pumped phosphor coated light-emitting diodes, optically pumped nano-crystal light-emitting diodes or other similar devices as would be readily understood by a worker skilled in the art. Furthermore, the term light-emitting element is used to define the specific device that emits the radiation, for example a LED die, and can equally be used to define a combination of the specific device that emits the radiation together with a housing or package within which the specific device or devices are placed.

As used herein, the term "about" refers to a +/-10% variation from the nominal value. It is to be understood that such a variation is always included in a given value provided herein, whether or not it is specifically referred to.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The present invention provides an optical feedback system for a light-emitting element luminaire which comprises a plurality of light-emitting elements configured to emit light. The optical feedback system comprises a primary mixing chamber which is optically coupled to the plurality of light-emitting elements and this primary mixing chamber provides for the mixing of the light which is generated by the plurality of light-emitting elements.

Optically coupled to the primary mixing chamber is a light collection device which enables the extraction and collection of a sample of the light emitted by the plurality of light-emitting elements. The light collection device includes a light entry aperture, which is optically coupled and positioned relative to the primary mixing chamber in such a manner that the sample of the light which is collected by the light collection device has a desired level of homogeneity with respect to the individual luminous flux output of each of the plurality of light-emitting elements. The light collection device guides this sample of the light to the light sensing device which enables the detection of the light, and thus the evaluation of the characteristics of the light emitted by the plurality of light-emitting elements. The output from the light sensing device can be subsequently provided to and thus used for the control of the operation of the plurality of light-emitting elements, thereby providing a means for controlling the characteristics of the light output by the luminaire.

In embodiments of the present invention, the plurality of light-emitting elements are oriented relative to each other and/or the light collection device, in order to enhance the homogeneity of the sample of the light which is collected by the light collection device. By orienting the plurality of light-emitting elements in this manner, the effect of the typically non-homogeneous radiation patterns associated with the light-emitting elements can be mitigated thereby improving the sampling of the light emitted by the luminaire. In this manner the light contribution from each of the plurality of light-emitting elements, which is collected by the light collection device, can be substantially equal or have a relative difference which is within a desired threshold.

In one embodiment, the light-emitting elements are oriented such that they are configured in a radial rotational orientation relative to the plane of the substrate upon which they are mounted. In this configuration, the orientation of the plurality of light-emitting elements is substantially the same relative to a central location, for example the centre of the array of light emitting elements.

In another embodiment of the present invention, the plurality of light emitting elements are oriented in a free rotational configuration relative to the plane of the substrate upon which they are mounted. In a free rotational configuration, each of the plurality of light emitting elements are rotationally oriented such that the light contribution from each of the plurality of light-emitting elements, which is collected by the light collection device, is substantially equal or has a difference which is within a desired threshold.

Figure 1 illustrates a perspective view of a luminaire including an optical feedback system according to one embodiment of the present invention and Figure 2

illustrates a top plan view of the same luminaire. The luminaire comprises a plurality of light- emitting elements 15, which in Figure 1 are arranged into multiple groups 10. The plurality of light-emitting elements are configured to emit light and these light-emitting elements are positioned within a primary mixing chamber 20. The primary mixing chamber is configured to mix the light emitted by the light-emitting elements into a substantially mixed and uniform light for emission from the luminaire. Optically coupled to the primary mixing chamber 20 is a light collection device 30, which comprises a light entry aperture 40. The light collection device 30 is configured to sample a portion of the light emitted by the light-emitting elements and guide this light to the light sensing device 50, for detection of the characteristics of the light. Through the sampling of the characteristics of the overall light emitted by the plurality of light-emitting elements, a drive and control system associated with the luminaire can use these detected characteristics of the light to determine if modification of the operation of the plurality of light-emitting elements is required in order to enable the generation of a desired overall light emission from the luminaire, for example.

Primary Mixing Chamber

The primary mixing chamber is optically coupled to the plurality of light- emitting elements, and is configured to mix the light emitted thereby.

The primary mixing chamber can have a reflective wall surface and can have a perpendicular and axial cross sectional profile that extends between an entrance aperture and an exit aperture. The reflective wall surface can assist with beam shaping and color mixing. The cross sectional profile of the primary mixing chamber can have an axial symmetric shape or an asymmetric shape or other desired shape as is known in the art. The axial cross sectional profile can flare or taper towards the exit aperture. The primary mixing chamber can have a circular, triangular, square, hexagonal, octagonal or other perpendicular cross section as would be readily understood by a worker skilled in the art.

In one embodiment the axial cross sectional profile of the primary mixing chamber can be straight, parabolic, elliptic, hyperbolic or other shape as would be readily understood by a worker skilled in the art. In one embodiment, the axial cross sectional profile can comprise a plurality of straight or curved segments, or a combination thereof.

In one embodiment the primary mixing chamber is configured as a dielectric total internal reflection type collector (DTIRC) such as a compound parabolic collector (CPC), or may comprise a mirror type reflective optic such as a reflective CPC, or other optic as would be readily understood by a worker skilled in the art.

In one embodiment of the present invention, the primary mixing chamber comprises a reflective base or the like, which can be configured to substantially surround the plurality of light emitting elements, for example substantially cover the substrate upon which plurality of light-emitting elements are mounted, in order to provide further reflection of the light emitted by light-emitting elements.

In one embodiment of the present invention, the reflective base is formed by coating the substrate upon which the plurality of light-emitting elements are mounted, with a reflective or coating. In another embodiment, the reflective based can be formed as a cover which can be placed on top of the substrate, wherein the cover is reflective and is configured to surround the plurality of light-emitting elements.

Light Collection Device

The light collection device is optically coupled to the primary mixing chamber, and is configured to sample a portion of the light generated light-emitting elements for detection thereof. The light collection device comprises a light entry aperture, which is positioned relative to the primary mixing chamber in order that the sample of the light has a desired level of homogeneity, for example, such that each of the plurality of light-emitting elements have a desired level of contribution to the sampled light. The light collection device is configured to provide the light sample to the light sensing device to which it is optically coupled.

In one embodiment of the present invention, the light entry aperture can be configured as a notch, hole, slit, plurality of holes or other aperture format as would be readily understood by a worker skilled in the art, or the light entry aperture can further be a combination thereof. In one embodiment of the present invention, the light sensing device is positioned proximate to the light entry aperture.

In one embodiment of the present invention, the light collection device further comprises a light collection optic optically coupled to the light entry aperture, wherein the light collection optic guides the sampled light to the light sensing device which is positioned at a location removed from the location of the light entry aperture.

This light collection optic can be a solid or hollow light pipe, can have refractive and/or reflective optical elements and can have diffuse or specular reflecting surfaces, for example. This light collection optic can provide a means for collecting and

guiding the light to the light sensing device. In one embodiment of the present invention, the light collection optic can further mix the collected light.

The light entry aperture is positioned relative to the primary mixing chamber such that the non-homogeneous radiation pattern of the plurality of light-emitting elements can be mitigated and further such that the light captured through the light entry aperture comprises a desired level of contribution from all of the plurality of light-emitting elements. In one embodiment, the light entry aperture is positioned at a radial location which is located between about 20° and about 60° from a horizontal axis. In another embodiment the light entry aperture is positioned at a radial location between about 30° and about 50° from the horizontal axis. In another embodiment the light entry aperture is positioned at a radial location between about 30° and about 40° from the horizontal axis. In one embodiment of the present invention, as illustrated in Figure 1 and shown schematically in Figure 3 A, the light entry aperture 100 can be positioned at a radial location about 35° from the horizontal axis. Furthermore, the light entry aperture is positioned at a height referenced to the plane of the plurality of light-emitting elements, wherein this height is determined in order to substantially reduce the contribution differences of each of the plurality of light-emitting elements relative to their respective location. For example, as illustrated in Figures 3A, 3B and 3 C, three light-emitting element positions were used to evaluate an adequate height of the light entry aperture relative to the position of the light-emitting element. For example, Figures 3A, 3B and 3C illustrate a light-emitting element at 0°, 30° and 60° from the horizontal, respectively. These locations of the light-emitting elements were used to evaluate the respective contributions of each of these light-emitting elements to the light captured by the light entry aperture 104, when the light entry aperture is positioned at different vertical locations relative to the primary mixing chamber 105.

Figure 4 illustrates a relationship 110 which represent the correlation between the level of equality of light-emitting element contribution to the sampled light (vertical axis) relative to the vertical location of the light entry aperture (horizontal axis) which is optically coupled to the primary mixing chamber. In Figure 4, the level of equality is defined as E _m i _n /E _max , wherein a value of 1 is representative of about an equal contribution from all of the plurality of light-emitting elements to the sampled light. As is clearly evident from Figure 4, as the height of the light entry aperture increases, the level of equality of the contribution of each of the light-emitting elements increases. Having particular regard to Figure 4, it is clear that the level of equality of the light-emitting element contribution is starting to plateau at a

height of about 30 mm, wherein the level of equality of light-emitting element contribution to the sampled light, or the homogeneity of the sampled light is about 94%.

In one embodiment of the present invention, the light entry aperture is optically coupled to the primary mixing chamber at substantially the top of the primary mixing chamber. In one embodiment, light entry aperture is distanced from the plurality of light-emitting elements between about 25mm and about 40 mm along the length of the primary mixing chamber. In another embodiment of the present invention the light entry aperture is distanced about 30 mm from the plurality of light-emitting elements.

In one embodiment of the present invention, the light collection device further comprises an optical element for example a lens, positioned therein to provide a means for concentrating and/or focusing the light collected by the light collection device onto the light sensing device. This process of concentration may increase the amount of light incident upon the light sensing device which may thereby increase the accuracy thereof.

In one embodiment, the optic positioned within the light collection device can directly re-image the exit aperture of the light collection device onto the light sensing device thereby reducing noise levels and increasing light flux onto the light sensing device.

In another embodiment of the present invention, the light collection device comprises a filter positioned at a position along the length of the light collection device. For example, this filter can be positioned at the top, bottom or middle of the light collection device. The filter can be a neutral filter to reduce the overall signal level or a selective filter such as an infrared filter, ultraviolet filter, or color filter to selectively block regions of the electromagnetic spectrum. The selection of the filter type can be based on the desired filtering capabilities thereof and the requirements of the specific application, for example the type of optical sensor. For example, daylight and light emitted by incandescent and fluorescent sources contains significant infrared content that can affect the light detection means, and therefore suppression using an infrared filter may be desired.

In one embodiment of the present invention the light collection device comprises a light blocking element, for example an optic or other structure, that may be used to limit the detection of ambient light, through undesired entry into the light collection device through the light entry aperture. For example, an opaque or reflective element may be placed such that all or part of the ambient light is prevented from entering the light collection device and/or prevented from reaching the light sensing device.

Light Sensing Device

The light sensing device is optically coupled to the light collection device and is configured to detect the sample of the light collected by the light collection device, and subsequently convert the sampled light incident thereon into one or more signals for subsequent use by a drive and control system associated with the luminaire. For example, the one or more signals can be used during the determination of subsequent drive signals for the plurality of light-emitting elements in order that light having desired characteristics can be generated by the luminaire.

A light sensing device can include one or more optical sensors. For example, the optical sensors may be semiconductor photodiodes, photosensors, LEDs phototransistors, photoresistors, photovoltaic cells, phototubes, photomultiplier tubes, other formats of light- to-voltage converters, light-to-frequency converters or other optical sensors, as would be readily understood by a worker skilled in the art. In addition, an optical sensor may be configured to detect light of one or more frequency ranges. In general, one or more optical sensors may be used. In one embodiment, the outputs of each of the plurality of light-emitting elements is monitored via a single optical sensor. In another embodiment, a separate optical sensor is used for each type of light- emitting element, for example, for each color in a multicolor light source.

In one embodiment, the one or more optical sensors are mounted within the light source on a respective printed circuit board. In another embodiment, at least some of the one or more optical sensors are mounted on the same printed circuit board as one or more of the plurality of light-emitting elements.

An optical sensor can be a narrow band optical sensor or a broad band optical. In one embodiment, a broadband sensor is mated with a filter, which can thereby provide the capability of a narrow band optical sensor. For example a silicon photodiode with color filter coatings for red, green, blue, amber or infrared radiation can be used to detect selected portions of the light sampled by the light collection device.

Light-Emitting Elements The luminaire generally comprises a plurality of light-emitting elements. As defined above, the plurality of light-emitting elements may optionally comprise a light- emitting element package comprising, in various combinations, a housing, an output optics (e.g., a lens such as a hemispherical lens, a filter, a coating, etc.), a drive circuitry and the like. In one embodiment, a light-emitting element is mounted to the luminaire via a substrate

operatively coupled to a drive circuitry configured to drive the light-emitting element. For instance, a light-emitting element may be driven via a printed circuit board (PCB) or the like, which may either be specifically configured for driving a single light-emitting element, or configured for driving a group or array of light-emitting elements connected in various serial and/or parallel configurations.

The light-emitting elements may be of various types, for example they may be LEDs, small molecule organic LEDs (OLEDs), polymer LEDs (PLEDs), or other primary or secondary emission light-emitting element or other format of a light-emitting element as would be readily understood. In one embodiment, each light-emitting element is generally configured to emit light in a forward direction, namely in a direction along the optical axis of the light- emitting element, or of a package thereof. Light emitted by such light-emitting elements generally comprises a significant axial component and a lesser radial component. For instance, a majority of the light emitted by these light-emitting elements is generally concentrated within a solid angle around the optical axis of the light-emitting element and/or package, whereas only a minor fraction of the light is emitted radially or sideways.

Furthermore, in one embodiment, the plurality of light-emitting elements comprises light-emitting elements which have a respective emission spectrum or color. These may include different types of high-brightness light-emitting elements, and/or other types of standard and/or regular intensity light-emitting elements. In one such embodiment, the light source comprises three light-emitting elements including of a red light-emitting element, a green light-emitting element and a blue light-emitting element, the combined outputs of which being controllable to provide a desired colored or white light output. In another such embodiment, the light source comprises four light-emitting elements including of a red light- emitting element, an amber light-emitting element, a green light-emitting element and a blue light-emitting element, the combined outputs of which again being controllable to provide a desired colored or white light output. Other such color combinations would be apparent to a worker skilled in the art.

In another embodiment, the plurality of light-emitting elements comprise one or more groups or arrays of light emitting elements, each group or array having a respective emission spectrum or color. These one or more groups or arrays may include different types of high-brightness and/or other types of standard and/or regular intensity light-emitting elements. In one such embodiment, the light source comprises three groups or arrays of light- emitting elements including a group or array of red light-emitting elements, a group or array

of green light-emitting elements and a group or array of blue light-emitting elements, the combined outputs of which being controllable to provide a desired colored or white light output. In another such embodiment, the light source comprises four groups or arrays of light-emitting elements including of a group or array of red light-emitting elements, a group or array of amber light-emitting elements, a group or array of green light-emitting elements and a group or array of blue light-emitting elements, the combined outputs of which being controllable to provide a desired colored or white light output. In another embodiment of the present invention, an array of group of light-emitting elements can include light-emitting elements which emit light from two or more different wavelength ranges, for example a group or array can comprise one or more red light-emitting elements, one or more green light-emitting elements and one or more blue light-emitting elements. Other such color combinations would be apparent to a worker skilled in the art.

In one embodiment, the light-emitting elements within a group may emit various colors, for example, each group may contain red, green, and blue or red, green, blue and amber light-emitting elements for production of white light or the light-emitting elements may also emit white light of various color temperatures, for example phosphor coated LEDs or a combination thereof.

In one embodiment of the present invention, the plurality of light-emitting elements are formed into a plurality of groups, wherein a group comprises light-emitting elements which emit light of different colors. Furthermore, the light-emitting elements associated with a particular group can be oriented in a predetermined fashion in order that a each of the light-emitting elements of the group have a substantially similar contribution to the light sampled by the light collection device.

For example, Figures 1 and 2 illustrate the plurality of light-emitting elements arranged into four groups of light-emitting elements arranged radially around a central location. These groups of light-emitting elements comprise a red 14, blue 12, green 11 and white 13 light-emitting elements.

In one embodiment of the present invention, the plurality of light-emitting elements are positioned in one or more circular patterns, wherein each of the plurality of light-emitting elements are rotated radially depending on the location thereof. An example of this orientation of the light-emitting elements is illustrated in Figure 5. In addition, as illustrated in Figure 5, the plurality of light-emitting elements can include an desired light- emitting element pattern comprising red 120, green 121 and white 122 light-emitting elements. Other color patterns of the light-emitting elements would be readily understood by

a worker skilled in the art and can be based on the desired color gamut and/or luminous flux output of the luminaire.

In another embodiment of the present invention, the plurality of light-emitting elements are positioned in one or more circular patterns, wherein each of the plurality of light-emitting elements are free rotated depending on the location thereof, relative to the light entry aperture. An example of this orientation of the light-emitting elements is illustrated in Figure 6. hi this configuration, orientation of each of the plurality of light-emitting elements is rotated in such a manner that the level of equality of light-emitting element contribution to the sampled light is at a predetermined level. In addition, as illustrated in Figure 6, the plurality of light-emitting elements can include an desired light-emitting element pattern comprising red 130, green 131 and white 132 light-emitting elements. Other color patterns of the light-emitting elements would be readily understood by a worker skilled in the art and can be based on the desired color gamut and/or luminous flux output of the luminaire.

Figure 7 illustrates a relationship 110 which represents the correlation between the level of equality of light-emitting element contribution to the sampled light (vertical axis) relative to the vertical location of the light entry aperture (horizontal axis) which is optically coupled to the primary mixing chamber, when the orientation of the light-emitting elements is rotated radially. Also illustrated in Figure 7 is a relationship 111 which represents the correlation between the level of equality of light-emitting element contribution to the sampled light (vertical axis) relative to the vertical location of the light entry aperture (horizontal axis) which is optically coupled to the primary mixing chamber, when the orientation of the light-emitting elements is freely rotated. In Figure 7, the level of equality is defined as E _min /E _max , wherein a value of 1 is representative of about an equal contribution from all of the plurality of light-emitting elements to the sampled light. As is clearly evident from Figure 7, as the height of the light entry aperture increased, the level of equality of the contribution of each of the light-emitting elements increases. Having particular regard to Figure 7, it is clear that the level of equality of the light-emitting element contribution is starting to plateau at a height of about 30 mm, wherein a level of equality of light-emitting element to the sampled light is about 94% when the orientation of the light-emitting elements is rotated radially. Having further regard to Figure 7, it is clear that the level of equality of the light-emitting element contribution also starts to plateau at a height of about 30 mm, wherein a level of equality of light-emitting element to the sampled light or the homogeneity of the sampled light is about 97.5% when the orientation of the light-emitting elements is freely rotated. As such by freely rotating each of the plurality of light-emitting elements, wherein

the free degree of free rotation is determined by the particular light-emitting elements location, can increase in the homogeneity of the contribution of each of the light-emitting elements to the sample of light collected by the light collection device.

The invention will now be described with reference to specific examples. It will be understood that the following examples are intended to describe embodiments of the invention and are not intended to limit the invention in any way.

EXAMPLE

Figure 1 illustrates a perspective view of a luminaire including an optical feedback system according to one embodiment of the present invention and Figure 2 illustrates a top plan view of the same luminaire. The luminaire comprises a plurality of light- emitting elements 15, which in Figure 1 are arranged into multiple groups 10 of light- emitting elements. As illustrated, each of the groups 10 of light-emitting elements comprises green 11, blue 12, red 13 and white 14 light-emitting elements, which are oriented into a substantially formation which is radially rotated relative to the location of the group.

Furthermore, the light-emitting elements of a particular group can be rotated relative to the other light-emitting elements in the group, wherein this relative rotation of the group and the individual light-emitting elements can provide for increasing the level of equality of light- emitting element contribution to light sampled by the light collection device 30. The plurality of light-emitting elements are configured to emit light and these light-emitting elements are positioned within a primary mixing chamber 20. The primary mixing chamber is configured to mix the light emitted by the light-emitting elements into a substantially mixed an uniform light for emission from the luminaire. The primary mixing chamber can include a reflective cover 60, which substantially surrounds the plurality of light-emitting elements and can enable the further reflection of the light generated by the plurality of light-emitting elements towards the exit aperture of the primary mixing chamber.

Optically coupled to the primary mixing chamber 20 is a light collection device 30, which comprises a light entry aperture 40. The light collection device 30 is configured to sample a portion of the light emitted by the light-emitting elements and guide this light to the light sensing device 50, for detection of the characteristics of the light.

Through the sampling of the characteristics of the overall light emitted by the plurality of light-emitting elements, a drive and control system associated with the luminaire can use these detected characteristics of the light in order to modify the operation of the plurality of light-emitting elements to enable the generation of a desired overall light emission from the

luminaire, for example a desired color, correlated color temperature, luminous flux output or other light characteristic as would be readily understood by a worker skilled in the art. It is obvious that the foregoing embodiments of the invention are examples and can be varied in many ways. Such present or future variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.