WO2012085822A2

WO2012085822A2 - System and method for illumination control

Info

Publication number: WO2012085822A2
Application number: PCT/IB2011/055784
Authority: WO
Inventors: Jorrit Ernst DE VRIES; Egbert Lenderink; Dirk Jan VAN KAATHOVEN; Ralph Kurt
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2010-12-22
Filing date: 2011-12-19
Publication date: 2012-06-28
Also published as: WO2012085822A3

Abstract

Systems and methods of illumination are provided. At least four solid state light sources are operable to emit light through a reflector. A plurality of target color points are identified based on respective target color temperatures of each of the plurality of target color points. The operation of an illumination system is controlled to generate a mixed white light by adjusting duty cycles of the light sources monotonically relative to the respective target color temperatures across a continuous range of color temperatures.

Description

SYSTEM AND METHOD FOR ILLUMINATION CONTROL

Technical Field

[0001] The present invention is directed generally to systems and methods for providing mixed light. More particularly, various inventive methods and apparatus disclosed herein relate to controlling multiple LED light sources to provide mixed white light at a desired color point across a range of color temperatures.

Background

[0002] Digital lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Patent Nos. 6,016,038 and 6,211,626.

[0003] Mixed light at particular color points and color temperatures can be generated by combining light from a plurality of different sources. For example, primary colors of light, including white light from a white light source can be mixed to provide mixed light having a desired color point and color temperature. However, a problem arises when transitioning mixed light from light that matches a first color temperature to mixed light that matches a second color temperature that differs from the first. Known solutions to this problem change the duty cycles of the light sources to generate mixed light at the different color points and color temperatures. However, abrupt changes in duty cycles of existing solutions cause artifacts that can appear in the mixed light when it changes from mixed light matching the first color temperature to mixed light matching the second color temperature. These artifacts appear on objects being illuminated by the mixed light, and result in a less visually pleasing presentation.

[0004] Thus, there is a need in the art to provide an illumination system and method that provides mixed light from a plurality of light sources, where the light sources are robustly controlled to smoothly adjust mixed light across a continuous range of color temperatures.

Summary

[0005] The present disclosure is directed to inventive methods and apparatus for generating mixed light. For example, a plurality of light sources emits light that is mixed by various surfaces of a reflector. Duty cycles of the light sources are controlled to generate mixed light at a desired color point and color temperature. The duty cycles are further controlled to provide a smooth transition across a range of color temperatures so that the mixed light smoothly passes between color temperatures substantially free of visible artifacts.

[0006] Generally, in one aspect, an illumination system to generate light is provided. The illumination system includes a reflector and at least four solid state light sources that are operable to emit light through the reflector. The illumination system also includes a controller programmed to identify a plurality of target color points based on respective target color temperatures of each of the plurality of target color points. The controller is further programmed to control operation of the illumination system to generate a mixed white light by adjusting duty cycles of each of the at least four solid state light sources monotonically relative to the respective target color temperatures across a continuous range of color temperatures.

[0007] In some embodiments, the continuous range of color temperatures includes a range from 3000K to 6000K. In at least one embodiment, the at least four solid state light sources include a plurality of non-white light sources, and the controller receives a peak wavelength value and a spectral width value of each of the plurality of non-white light sources. The at least four solid state light sources may include at least one white light source, and in one

embodiment the controller is programmed to receive a color point of the at least one white light source. [0008] In at least one embodiment, the controller is programmed with a transfer function including coefficients established such that the transfer function provides a model of a monotonic function of the duty cycles relative to the respective target color temperatures. In one embodiment, each of the peak wavelength value and the spectral width value of the plurality of non-white light sources, and the color point of the at least one white light source, are provided as inputs to the transfer function. In various embodiments, the coefficients can be established such that the illumination system generates the mixed white light having a minimum CRI greater than 85. According to one embodiment, the coefficients are established to achieve the minimum CRI while maximizing a luminous flux output across the continuous range of color temperatures.

[0009] In one embodiment, a deviation of the mixed white light generated by the illumination system relative to the respective target color temperatures is less than 0.01 across the continuous range of color temperatures. In some embodiments, the deviation of the mixed white light generated by the illumination system relative to the respective target color temperatures is less than 0.006 where the target color temperature is in a color temperature range between 3000K and 6500K. In various embodiments, the illumination system includes a photosensitive detector and a lightguide. The photosensitive detector measures and provides feedback to the controller concerning a luminous flux generated by the at least four solid state light sources, and the lightguide provides light from the at least four solid state light sources to the photosensitive detector. In one embodiment, the illumination system includes at least five solid state light sources, each operable to emit light through the reflector, with the controller programmed to generate the mixed white light by adjusting duty cycles of each of the at least five solid state light sources.

[0010] In some embodiments, the controller is programmed to determine a monotonic function that includes a ratio of a duty cycle of a first light source and a duty cycle of a second light source across the continuous range of color temperatures. The monotonic function may include a polynomial function. In various embodiments, the controller is programmed to determine a first duty cycle of a first light sources and a second duty cycle of a second light sources, where a ratio of the first duty cycle to the second duty cycle provides a non-decreasing monotonic function across the continuous range of color temperatures. The second duty cycle provides a non-increasing monotonic function of the second light source across the continuous range of color temperatures.

[0011] In another aspect, a method of providing illumination from a lighting source having at least four solid state light sources is provided. The method includes an act of identifying a plurality of target color points based on respective target color temperatures of each of the plurality of target color points. The method also includes an act of generating a mixed white light emitted by the lighting source by adjusting duty cycles of each of the at least four solid state light sources such that the duty cycles are adjusted monotonically relative to the respective target color temperatures across a continuous range of color temperatures.

[0012] In one embodiment, the method includes an act or acts of receiving a target color temperature, a color point of at least one of the at least four light sources, and a peak wavelength value of a plurality of the at least four light sources. The method can also receive a spectral width value of at least one of the at least four solid state light sources, and determine a transfer function. The transfer function includes coefficients and provides a monotonic function of the duty cycles relative to color temperature based at least in part on the spectral width value and the peak wavelength value.

[0013] Generally, in yet another aspect, a computer readable medium is provided. The computer readable medium is encoded with a program for execution on a processor. The program, when executed on the processor performs a method of providing illumination from a lighting source having at least four solid state light sources. The method includes an act of identifying a plurality of target color points based on respective target color temperatures of each of the plurality of target color points. The method also includes an act of generating a mixed white light emitted by the lighting source by adjusting duty cycles of each of the at least four solid state light sources such that the duty cycles are adjusted monotonically relative to the respective target color temperatures across a continuous range of color temperatures.

[0014] In some embodiments, the program performs a method that includes acts of determining a first duty cycle of a first light source, and determining a second duty cycle of a second light, wherein a ratio of the first duty cycle to the second duty cycle provides a non- decreasing monotonic function across the continuous range of color temperatures. In one embodiment, the program performs a method that includes acts of receiving a target color temperature, a color point of at least one of the at least four light sources, and a peak wavelength value of a plurality of the at least four light sources. The method also includes acts of receiving a spectral width value of at least one of the at least four solid state light sources, and determining a transfer function including coefficients to provide a monotonic function of the duty cycles relative to color temperature based, at least in part, on the spectral width value and the peak wavelength value.

[0015] As used herein for purposes of the present disclosure, the term "LED" should be understood to include any electroluminescent diode or other type of carrier injection/junction- based system that is capable of generating radiation in response to an electric signal. Thus, the term LED includes, but is not limited to, various semiconductor-based structures that emit light in response to current, light emitting polymers, organic light emitting diodes (OLEDs), electroluminescent strips, and the like. In particular, the term LED refers to light emitting diodes of all types (including semi-conductor and organic light emitting diodes) that may be configured to generate radiation in one or more of the infrared spectrum, ultraviolet spectrum, and various portions of the visible spectrum (generally including radiation wavelengths from approximately 400 nanometers to approximately 700 nanometers). Some examples of LEDs include, but are not limited to, various types of infrared LEDs, ultraviolet LEDs, red LEDs, blue LEDs, green LEDs, yellow LEDs, amber LEDs, orange LEDs, and white LEDs (discussed further below). It also should be appreciated that LEDs may be configured and/or controlled to generate radiation having various bandwidths (e.g., full widths at half maximum, or FWHM) for a given spectrum (e.g., narrow bandwidth, broad bandwidth), and a variety of dominant wavelengths within a given general color categorization.

[0016] For example, one implementation of an LED configured to generate essentially white light (e.g., a white LED) may include a number of dies which respectively emit different spectra of electroluminescence that, in combination, mix to form essentially white light. In another implementation, a white light LED may be associated with a phosphor material that converts electroluminescence having a first spectrum to a different second spectrum. In one example of this implementation, electroluminescence having a relatively short wavelength and narrow bandwidth spectrum "pumps" the phosphor material, which in turn radiates longer wavelength radiation having a somewhat broader spectrum.

[0017] It should also be understood that the term LED does not limit the physical and/or electrical package type of an LED. For example, as discussed above, an LED may refer to a single light emitting device having multiple dies that are configured to respectively emit different spectra of radiation (e.g., that may or may not be individually controllable). Also, an LED may be associated with a phosphor that is considered as an integral part of the LED (e.g., some types of white LEDs). In general, the term LED may refer to packaged LEDs, non-packaged LEDs, surface mount LEDs, chip-on-board LEDs, T-package mount LEDs, radial package LEDs, power package LEDs, LEDs including some type of encasement and/or optical element (e.g., a diffusing lens), etc.

[0018] The term "light source" should be understood to refer to any one or more of a variety of radiation sources, including, but not limited to, LED-based sources (including one or more LEDs as defined above), incandescent sources (e.g., filament lamps, halogen lamps), fluorescent sources, phosphorescent sources, high-intensity discharge sources (e.g., sodium vapor, mercury vapor, and metal halide lamps), lasers, other types of electroluminescent sources, pyro-luminescent sources (e.g., flames), candle-luminescent sources (e.g., gas mantles, carbon arc radiation sources), photo-luminescent sources (e.g., gaseous discharge sources), cathode luminescent sources using electronic satiation, galvano-luminescent sources, crystallo- luminescent sources, kine-luminescent sources, thermo-luminescent sources, triboluminescent sources, sonoluminescent sources, radioluminescent sources, and luminescent polymers.

[0019] A given light source may be configured to generate electromagnetic radiation within the visible spectrum, outside the visible spectrum, or a combination of both. Hence, the terms "light" and "radiation" are used interchangeably herein. Additionally, a light source may include as an integral component one or more filters (e.g., color filters), lenses, or other optical components. Also, it should be understood that light sources may be configured for a variety of applications, including, but not limited to, indication, display, and/or illumination. An "illumination source" is a light source that is particularly configured to generate radiation having a sufficient intensity to effectively illuminate an interior or exterior space. In this context, "sufficient intensity" refers to sufficient radiant power in the visible spectrum generated in the space or environment (the unit "lumens" often is employed to represent the total light output from a light source in all directions, in terms of radiant power or "luminous flux") to provide ambient illumination (i.e., light that may be perceived indirectly and that may be, for example, reflected off of one or more of a variety of intervening surfaces before being perceived in whole or in part).

[0020] The term "spectrum" should be understood to refer to any one or more frequencies (or wavelengths) of radiation produced by one or more light sources. Accordingly, the term "spectrum" refers to frequencies (or wavelengths) not only in the visible range, but also frequencies (or wavelengths) in the infrared, ultraviolet, and other areas of the overall electromagnetic spectrum. Also, a given spectrum may have a relatively narrow bandwidth (e.g., a FWHM having essentially few frequency or wavelength components) or a relatively wide bandwidth (several frequency or wavelength components having various relative strengths). It should also be appreciated that a given spectrum may be the result of a mixing of two or more other spectra (e.g., mixing radiation respectively emitted from multiple light sources).

[0021] For purposes of this disclosure, the term "color" is used interchangeably with the term "spectrum." However, the term "color" generally is used to refer primarily to a property of radiation that is perceivable by an observer (although this usage is not intended to limit the scope of this term). Accordingly, the terms "different colors" implicitly refer to multiple spectra having different wavelength components and/or bandwidths. It also should be appreciated that the term "color" may be used in connection with both white and non-white light.

[0022] The term "color temperature" generally is used herein in connection with white light, although this usage is not intended to limit the scope of this term. Color temperature essentially refers to a particular color content or shade (e.g., reddish, bluish) of white light. The color temperature of a given radiation sample conventionally is characterized according to the temperature in degrees Kelvin (K) of a black body radiator that radiates essentially the same spectrum as the radiation sample in question. Black body radiator color temperatures generally fall within a range of from approximately 700 degrees K (typically considered the first visible to the human eye) to over 10,000 degrees K; white light generally is perceived at color temperatures above 1500-2000 degrees K.

[0023] The term "lighting fixture" is used herein to refer to an implementation or arrangement of one or more lighting units in a particular form factor, assembly, or package. The term "lighting unit" is used herein to refer to an apparatus including one or more light sources of same or different types. A given lighting unit may have any one of a variety of mounting arrangements for the light source(s), enclosure/housing arrangements and shapes, and/or electrical and mechanical connection configurations. Additionally, a given lighting unit optionally may be associated with (e.g., include, be coupled to and/or packaged together with) various other components (e.g., control circuitry) relating to the operation of the light source(s). An "LED-based lighting unit" refers to a lighting unit that includes one or more LED- based light sources as discussed above, alone or in combination with other non LED-based light sources. A "multi-channel" lighting unit refers to an LED-based or non LED-based lighting unit that includes at least two light sources configured to respectively generate different spectrums of radiation, wherein each different source spectrum may be referred to as a "channel" of the multi-channel lighting unit.

[0024] The term "controller" is used herein generally to describe various apparatus relating to the operation of one or more light sources. A controller can be implemented in numerous ways (e.g., such as with dedicated hardware) to perform various functions discussed herein. A "processor" is one example of a controller which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform various functions discussed herein. A controller may be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions. Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs). [0025] In various implementations, a processor or controller may be associated with one or more storage media (generically referred to herein as "memory," e.g., volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM, floppy disks, compact disks, optical disks, magnetic tape, etc.). In some implementations, the storage media may be encoded with one or more programs that, when executed on one or more processors and/or controllers, perform at least some of the functions discussed herein. Various storage media may be fixed within a processor or controller or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or controller so as to implement various aspects of the present invention discussed herein. The terms "program" or "computer program" are used herein in a generic sense to refer to any type of computer code (e.g., software or microcode) that can be employed to program one or more processors or controllers.

[0026] In one network implementation, one or more devices coupled to a network may serve as a controller for one or more other devices coupled to the network (e.g., in a master/slave relationship). In another implementation, a networked environment may include one or more dedicated controllers that are configured to control one or more of the devices coupled to the network. Generally, multiple devices coupled to the network each may have access to data that is present on the communications medium or media; however, a given device may be "addressable" in that it is configured to selectively exchange data with (i.e., receive data from and/or transmit data to) the network, based, for example, on one or more particular identifiers (e.g., "addresses") assigned to it.

[0027] The term "network" as used herein refers to any interconnection of two or more devices (including controllers or processors) that facilitates the transport of information (e.g. for device control, data storage, data exchange, etc.) between any two or more devices and/or among multiple devices coupled to the network. As should be readily appreciated, various implementations of networks suitable for interconnecting multiple devices may include any of a variety of network topologies and employ any of a variety of communication protocols.

Additionally, in various networks according to the present disclosure, any one connection between two devices may represent a dedicated connection between the two systems, or alternatively a non-dedicated connection. In addition to carrying information intended for the two devices, such a non-dedicated connection may carry information not necessarily intended for either of the two devices (e.g., an open network connection). Furthermore, it should be readily appreciated that various networks of devices as discussed herein may employ one or more wireless, wire/cable, and/or fiber optic links to facilitate information transport throughout the network.

[0028] The term "user interface" as used herein refers to an interface between a human user or operator and one or more devices that enables communication between the user and the device(s). Examples of user interfaces that may be employed in various implementations of the present disclosure include, but are not limited to, switches, potentiometers, buttons, dials, sliders, a mouse, keyboard, keypad, various types of game controllers (e.g., joysticks), track balls, display screens, various types of graphical user interfaces (GUIs), touch screens, microphones and other types of sensors that may receive some form of human-generated stimulus and generate a signal in response thereto.

[0029] The term "monotonic" should be understood to refer to functions f(x) in which for all values of x, y either: an increasing value of x results in an increasing or non-changing value of y; or, an increasing value of x results in a decreasing or non-changing value of y. It should be appreciated that the term "monotonically" refers to a relationship between parameters that have the immediately preceding characteristics relative to one another.

[0030] The term "primary color" should be understood to refer to any color provided by a discrete light source, whether provided by a color LED, a phosphor alone or in combination with a filter, lens or other optical component. A primary color includes any color that can be combined with at least one other primary color to create a secondary color. It should be appreciated that the term "primary color" may be used in connection with a discrete light source that emits radiation at any frequency.

[0031] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It should also be appreciated that terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.

Brief Description of the Drawings

[0032] In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.

[0033] FIG. 1 illustrates a block diagram of an illumination system in accordance with an embodiment;

[0034] FIG. 2 illustrates a perspective view of an illumination system in accordance with an embodiment;

[0035] FIG. 3 illustrates a graph of light source duty cycle ratios as a function of color temperature in accordance with an embodiment;

[0036] FIG. 4 illustrates a graph of light source duty cycle as a function of color temperature in accordance with an embodiment;

[0037] FIG. 5 illustrates a graph of light source duty cycle ratios as a function of color temperature in accordance with an embodiment;

[0038] FIG. 6 illustrates a graph of light source duty cycle ratios as a function of color temperature in accordance with an embodiment;

[0039] FIG. 7 illustrates a graph of light source duty cycle ratios as a function of color temperature in accordance with an embodiment;

[0040] FIG. 8 illustrates a graph of light source duty cycle ratios as a function of color temperature in accordance with an embodiment; [0041] FIG. 9 illustrates a flow chart of a method of providing illumination from a lighting unit in accordance with an embodiment; and

[0042] FIG. 10 illustrates a flow chart of a method of providing illumination from a lighting unit in accordance with an embodiment.

Detailed Description

[0043] Abrupt changes in duty cycles that control light sources to provide mixed light at different color temperatures remains a problem. Applicants have recognized and appreciated that it would be beneficial to find smoothly transitioning duty cycles that emit light across a continuous range of color temperatures without unwanted visible artifacts that can appear due to abrupt duty cycle changes. In view of the foregoing, various embodiments and

implementations of the present invention are directed to generate a mixed white light by adjusting duty cycles of the light sources monotonically relative to the respective target color temperatures across a continuous range of color temperatures.

[0044] Referring to FIG. 1, in one embodiment, illumination system 100 includes at least one lighting unit 105. Lighting unit 105 includes a plurality of solid state light sources 110. For example, each light source 110 may include one or more LEDs that emit light of a primary color, such as red, green, blue, cyan, amber, royal, deep red, or white, among others. The LEDS may be encapsulated with domes, or may be free of encapsulation. In one embodiment, lighting unit 105 includes at least four light sources 110, and each of the four light sources 110 is configured to emit light of a different primary color. Lighting unit 105 can also include at least one controller 115, at least one photosensitive detector 120, and at least one temperature sensor 125. Controller 115 generally determines duty cycles of control signals that operate light sources 110, based for example on information from photosensitive detector 120, temperature sensor 125, or predetermined information or desired outputs, such as a desired color temperature. In one embodiment, controller 115 determines duty cycles that smoothly transition mixed light emitted from illumination system 100 from a first color temperature to a second color temperature. Controller 115 can be included in lighting unit 105, or separate from lighting unit 105. [0045] In one embodiment, light source 110 includes at least one compound light source. For example, controller 115 can generate a compound light source based on the color points and flux values of two or more light sources 110. In this example, two light sources 110, such as red and amber are relatively close to each other in a gamut when compared to blue, green, or white light sources 110. Controller 115 may generate a compound light source located between red and amber light sources 110, for example by summing the fluxes and determining a color point closest to these two light sources 110. By merging red and amber (or any other) combination of light sources 110 into a single compound light source, the number of light sources 110 is effectively reduced by at least one, for example, from five to four for the duty cycle calculations performed by controller 115. With this approach, controller 115 can determine one duty cycle for the compound light source, and can apply this duty cycle to each of the two light sources (e.g., red and amber), which reduces the amount of information that is processed by controller 115.

[0046] In one embodiment, controller 115 operates light sources 110 at their calculated duty cycles. Lighting unit 105 mixes the light emitting from light sources 110 to provide a mixed light that can be output from lighting unit 105 to illuminate an object at the desired color temperature with optimum output characteristics. For example, controller 115 can determine individual duty cycles of light sources 110 so that the mixed output light has a maximum achievable flux and a high CRI, (e.g., a CRI of 85 or higher) across a range of color temperatures. Controller 115 can also determine duty cycles for light sources 110 that have monotonic characteristics between different color temperatures.

[0047] FIG. 2 depicts an example of illumination system 100. With reference to FIG. 2, in one embodiment, a plurality of light sources 110 are arranged to emit light toward at least one reflector 205. Reflector 205 includes a reflective inner surface, an entrance aperture, and an exit aperture that in one embodiment is larger than the entrance aperture. Light sources 110 may form an array that emits light into the entrance aperture and out from the exit aperture, through reflector 205. The light can be collimated into a mixed white light beam with a hard edge operable, for example, as a projected spot light in a theater. Reflector 205 can be a tubular reflector, or various other shapes, including cylindrical and polygonal. In one embodiment, illumination system 100 includes a plurality of lightguides 210. Light from at least one light source 110 follows at least one lightguide 210 to photosensitive detector 120, which can sense the luminous flux of respective light source 110 and pass this information to controller 115.

[0048] In one embodiment, luminous flux and wavelength characteristics of light emitted from light sources 110 changes with time, use, and/or temperature. For example, LED drive currents or LED duty cycles can affect the temperature of light sources 110, which in turn affects the peak output wavelength of light sources 110. In one embodiment, photosensitive detector 120 senses the flux and temperature sensor 125 senses the temperature of at least one light source 110 and provides this information to controller 115. Based on the sensed temperature feedback, (e.g., temperature sensor 125 monitors a temperature of a substrate upon which light source 110 is mounted,) controller 115 predicts future light source

temperature, and adjusts the color points of light sources 110 to account for estimated future temperature fluctuations. Based on the sensed flux information and calibrated (e.g., factory determined) flux values of light sources 110, controller 115 can determine that the duty cycle ratios of light sources 110 with respect to each other are changing, or will change, and can adjust the duty cycle ratios of light sources 110 to keep their ratios constant so that the mixed output light emitted from lighting unit 105 maintains maximum flux and a high CRI (e.g. 85 or above) at the desired color temperature.

[0049] In some embodiments, controller 115 executes a transfer function to determine duty cycles of light sources 110 that, when mixed, provides light at desired color temperatures. For example, a desired color temperature of the mixed output light of lighting unit 105, as well as peak wavelength values of non-white light sources 110 (e.g., red, green, amber, and blue) and the color point of a white light source 110 can be received as input by controller 115. In one embodiment, controller 115 need not receive luminous flux values of light from light sources 110 as input, because the relation between luminous flux values and the duty cycles of the corresponding light source 100 is linear. Controller 115 can correct for changing luminous flux with a linear scaling operation. In one embodiment, because the relation between wavelength and duty cycle is non-linear, controller 115 is programmed to model quadratic function(s) of the duty cycle of light sources 110 relative to the color temperature of light emitted from illumination system 100 with a transfer function to adjust duty cycles of light sources 110 to accommodate for changes to wavelengths due, for example, to temperature or time of operation.

[0050] In one embodiment, the transfer function executed by controller 115 generates duty cycles for light sources 110 based on the influence of peak wavelengths and spectral widths of non-white light sources 110 (e.g., Blue B, Green G, Amber A, and Red R), the color points (x, y) of a white light source 110, and the desired color temperature of the mixed output light, as represented by a second order function such as equation (1):

[0052] With reference to equation 1, controller 115 determines the duty cycles of color light sources 110 (DC_B for blue, DC_G for green, DC_A amber, DC_R for red and DC_W for white) by executing the transfer function represented by the matrix of equation 1. The peak wavelengths of the color light sources 110 are represented by λ_χ, the spectral widths of color light sources 110 are represented by Δ λ_χ, the color points of a white light source 110 are represented by x_w, y_w„ the desired color temperature is represented by CCT (correlated color temperature). In equation (1), the superscript V indicates a transposed vector. In one embodiment, the matrix coefficients A, B, C, are 5x5 matrices determined in a designed experiment manner by using random points in the parameter space as input to determine the optimum duty cycles for light sources 110, with the results combined into transfer function coefficients A, B, and C.

[0053] Utilizing the transfer function of equation (1) to find a smooth relation with monotonic characteristics across a color temperature range of, for example, greater than 1000K requires in one embodiment a subtle balancing of weight factors in the optimization process in order to determine duty cycles of light sources 110 for a desired color temperature. For example, giving too much weight to reaching an exact color point with minimal deviation can result in abrupt duty cycle changes with color temperature and instable lighting unit 105 operation. Accordingly, in various embodiments, the set of duty cycles employed at the test points in the parameter space are optimized to provide a balance of achieving the correct color point, maximizing the luminous flux output and providing a high CRI. In one embodiment, the greatest weight is given to the accuracy with which the target color point is achieved while maximizing luminous flux. In this embodiment, achieving a high CRI is given a lesser weight.

[0054] In one embodiment, illumination system 100 includes blue, green, amber, red, and white (e.g. neutral white) light sources 110 with saturated colors of at least 148 Im for blue, 1700 Im for green, 873 Im for amber, 709 Im for red, and 4700 Im for white. These numbers are examples, and in another embodiment, the luminous flux of light sources 110 is at least 235 Im for blue, 2608 Im for green, 1289 Im for amber, 1048 Im for red, and 5808 Im for white. The color temperature of the light output from lighting unit 105 can vary within a predetermined range. For example, in one embodiment, the light output from lighting unit 105 ranges between 2700K and 6500K.

[0055] In one embodiment, illumination system 100 includes blue, green, amber, and red light sources 110 with peak wavelengths of 448.5 nm, 515.9 nm, 599.6 nm, and 642.1 nm, respectively, and a white light source 110 with an (x, y,) color point of (0.3895, 0.3798). In this example, illumination system 100 provides saturated colors having flux values of at least 148 Im for blue, 1700 Im for green, 873 Im for amber, 709 Im for red, and 4700 Im for white. In another example having these wavelengths and color points, the flux values are at least 235 Im for blue, 2608 Im for green, 1289 Im for amber, 1048 Im for red, and 5808 Im for white. In this example, the CRI is larger than 85, and acceptable deviation from the target colored point along a black body locus within a gamut is expressed in equation (2) as:

(2) [0056] In this example, the standard deviation of color provided by illumination system 100 is less than 0.01 sdcm in the full range of the color temperature, and smaller than 0.006 sdcm for the range of color temperature from 3000K to 6500K. Other levels of standard deviation can be provided in various embodiments.

[0057] Continuing with the above example, the duty cycles determined by controller 115 for blue, green, amber, and white color light sources 110 relative to the duty cycle of red light source 110 as a function of color temperature are illustrated in FIG. 3. The duty cycle curves illustrated in FIG. 3 can also be represented as quadratic functions, also shown in FIG. 3. The quadratic functions represent the smooth transfer functions relating to the relative duty cycles of light sources 110 across the range of color temperatures. In one embodiment, controller 115 determines duty cycles having monotonic characteristics across a range of color temperatures. With reference to FIG. 3, the white, green, amber, and blue light source 110 duty cycles of the non-white light sources 110, relative to red light source 110 are each non-decreasing monotonic functions across the range of color temperatures from approximately 3000K to 6500K. According to some embodiments, the duty cycles of the non-white light sources 110, relative to red light source 110 are each strictly increasing monotonic functions. In the illustrated example green color source 110 exhibits a non-decreasing monotonic function (that is also strictly-increasing) from 3000K to 6000K, where the green/red duty cycle ratio smoothly increases from approximately 0.75 at 2500K to 5.25 at 6000K, as represented by the quadratic function of equation (3): y = 9E-08x² + 0.0004x - 1.3413 (3)

[0058] The duty cycle of red light source 110 as a function of color temperature are illustrated in FIG. 4, with its corresponding quadratic function that represents the smooth transfer function of the duty cycle of red light source 110 across the range of color

temperatures from approximately 3000K to 6500K, and depicts a non-increasing monotonic function. FIG. 5, FIG. 6, FIG. 7, and FIG. 8 respectively depict the monotonic characteristics of the ratio of duty cycles for blue, green, amber, and white light sources 110, with respect to red light source 110 across a range of color temperatures, together with their representative quadratic functions. With reference to FIGS. 5 - 8, concept A illustrates the duty cycles where the LEDs of light source 110 include a dome, and concept C illustrates the duty cycles where the LEDs are free of encapsulation by a dome. Although quadratic functions are illustrated, in accordance with various embodiments, other polynomial functions (e.g., cubic) can be employed to approximate the curve provided by the duty cycle as a function of color temperature.

[0059] In one embodiment, the duty cycle ratios are segmented monotonic functions across a series of color temperature ranges. For example, light source 110 duty cycles can include a first monotonic function that is non-increasing from 2500K to 4500K, and a second monotonic function that is non-decreasing from 4500K to 6000K. In this example, an inflection point exits at 4500K so that the duty cycles, in this example, do not exhibit a single monotonic function over the range of continuous color temperatures from 2500K to 6000K, but rather two segmented monotonic functions over this range. These color temperatures and segments are examples, and other segments (e.g., across a range greater than 1000K) are possible.

[0060] FIG. 9 illustrates a flow chart of a method 900 of providing illumination from a lighting unit. In one embodiment, method 900 includes an act of receiving a color point of at least one light source (ACT 905). For example, a plurality of (e.g., at least four) light sources may include at least one white light source, and receiving a color point (ACT 905) includes receiving the (x, y) color point coordinates of the white light source on the black body locus. Method 900 can also include an act of receiving the spectral width value of light emanating from light sources (ACT 910). In one embodiment, spectral width values of a plurality of (e.g. at least four) light sources are received (ACT 910) for each non-white light source. In one embodiment, receiving the spectral width value of light from a light source (ACT 910) includes receiving an indication of a wavelength interval over which the magnitude of spectral components of the light is greater than a specified fraction of the magnitude of the component at the maximum value, e.g., the full width of the spectral interval at half-maximum.

[0061] In some embodiments, method 900 includes acts of receiving the peak wavelength value of light emanating from at least one light source (ACT 915), and receiving a target color temperature (ACT 920). For example, peak wavelength values can be received (ACT 915) from a plurality of light sources. In one example, at least one target color temperature can be received (ACT 920) from a user as a desired color temperature, where mixed light from a plurality of light sources are operated together to achieve the desired color temperature.

[0062] In one embodiment, method 900 determines transfer function coefficients (ACT 925). For example, transfer function coefficients can be determined (ACT 925) for a second order transfer function such as that of equation (1) above. In some embodiments, the transfer function coefficients are determined using information concerning a known set of at least four solid state light sources, for example, the color point of at least one white solid state light source (ACT 905), the peak wavelength of a plurality of non-white solid state light sources (ACT 915), and the corresponding spectral width of the plurality of non-white light sources (ACT 910). According to some embodiments, the illumination system includes a quantity of n non-white sold state light sources. I n one embodiment, the illumination system is constructed with n≥ 3 non-white light sources. In another embodiment, the illumination system is constructed with n ≥ 4 non-white light sources. In some versions of these embodiments, a compound light source is not employed in the method 900. According to the immediately preceding approach, the transfer function is employed for control of the duty cycles of each of the n light sources where a monotonic relationship exists for the respective duty cycles relative to color temperature.

[0063] In some embodiments, the transfer function coefficients are determined (ACT 925) using a random set of target color temperatures (ACT 920) in combination with the information concerning the known set of at least four solid state light sources. I n one embodiment, the variation of color temperature through the random set of color temperature values allows the duty cycles to be adjusted to provide the monotonic relationship while optimizing the optical characteristics of the illumination system across a range of color temperatures.

[0064] In some embodiments, the controller is programmed with the transfer function and corresponding transfer function coefficients derived at ACT 925. Method 900, in some embodiments includes the acts of processing inputs with the transfer function (ACT 930) and controlling the duty cycles of light sources to generate mixed light (ACT 935) based on a user provided target color temperature received by the system (ACT 940). In some embodiments, the controller can be programmed to determine the transfer function coefficients. In these embodiments, the received color points (ACT 905), spectral width values (ACT 910), peak wavelength values (ACT 915), and the target color temperature (ACT 920) are all received by a controller programmed with a transfer function. The controller can determine transfer function coefficients from the received information (ACT 925), and process the received inputs (ACT 940) with the transfer function (ACT 930) to control duty cycles of the light sources to generate mixed white light (ACT 935).

[0065] FIG. 10 illustrates a flow chart of a method 1000 of providing illumination from a lighting unit. In one embodiment, method 1000 includes an act of receiving input parameters (ACT 1005). For example, input parameters can be received (ACT 1005) by a controller programmed with the transfer function of equation (1). In one embodiment, receiving input parameters (ACT 1005) includes identifying selected or received color points and achieving light at each of a plurality of desired color temperatures based on the known characteristics of the solid state light sources included in the lighting unit (for example, color point, peak wavelength and/or spectral width). The color points may be selected at random, or in a pattern across a range of color temperatures.

[0066] Method 1000 may also include an act of determining the relative weight of the input parameters (ACT 1010). For example, the relative weight of various parameters can be determined (ACT 1010) by optimizing a set of duty cycles of respective light sources to provide a balance between factors such as achieving the desired color point, maximizing flux of the mixed light, and providing a high CRI (e.g., 85 or more) while providing a monotonic relationship between changes in duty cycle and changes in color temperature. In one embodiment, method 1000 includes an act of generating transfer function coefficients (ACT 1015). For example, transfer function coefficients can be determined (ACT 1015) by determining a set of duty cycles as a function of color temperatures across a range of color temperatures. In this example, a curve fit (e.g., quadratic function) is generated to approximate the monotonic characteristics of the set duty cycles, and the transfer function coefficients are determined (ACT 1015) that model the monotonic characteristics of the sets of duty cycles.

[0067] The systems and methods described herein provide a robust control system to create and tune high quality mixed white light with at least four sold state light sources as part of an illumination system. The duty cycles of the light sources are smoothly adjusted to provide light that when mixed and output from a lighting unit, provides white light with the maximum achievable luminous flux and a high CRI, for a continuous range of color temperatures that matches the desired color point with minimal deviation. The transfer function translates desired color temperatures (for example selected by a user) to duty cycles of each light source. This transfer function smoothly transitions light from a first color temperature to a second color temperature, preventing visible artifacts due to abrupt changes in flux, color, or CRI associated with the change in color temperature.

[0068] While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[0069] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. [0070] The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

[0071] The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and/or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified.

[0072] As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of" or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e. "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0073] As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0074] It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

[0075] Any reference numerals or other characters, appearing between parentheses in the claims, are provided merely for convenience and are not intended to limit the claims in any way.

[0076] In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "composed of," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively.

What is claimed is:

Claims

1. An illumination system (100) configured to generate light, the illumination system comprising:

a reflector (205);

at least four solid state light sources (110), each solid state light source operable to emit light through the reflector; and

a controller (110) programmed

to identify a plurality of target color points based on respective target color temperatures of each of the plurality of target color points, and

to control operation of the illumination system to generate a mixed white light by adjusting duty cycles of each of the at least four solid state light sources

monotonically relative to the respective target color temperatures across a continuous range of color temperatures.

2. The illumination system of claim 1, wherein the continuous range of color temperatures includes a range from 3000K to 6000K.

3. The illumination system of claim 1, wherein the at least four solid state light sources include a plurality of non-white light sources, and wherein the controller is programmed to receive a peak wavelength value and a spectral width value of each of the plurality of non-white light sources.

4. The illumination system of claim 3, wherein the at least four solid state light sources include at least one white light source, and wherein the controller is programmed to receive a color point of the at least one white light source.

5. The illumination system of claim 4, wherein the controller is programmed with a transfer function including coefficients established such that the transfer function provides a model of a monotonic function of the duty cycles relative to the respective target color temperatures.

6. The illumination system of claim 5, wherein each of the peak wavelength value and the spectral width value of the plurality of non-white light sources, and the color point of the at least one white light source, are provided as inputs to the transfer function.

7. The illumination system of claim 5, wherein the coefficients are established such that the illumination system generates the mixed white light having a minimum CRI greater than 85.

8. The illumination system of claim 7, wherein the coefficients are established to achieve the minimum CRI while maximizing a luminous flux output across the continuous range of color temperatures.

9. The illumination system of claim 1, wherein a deviation of the mixed white light generated by the illumination system relative to the respective target color temperatures is less than 0.01 across the continuous range of color temperatures.

10. The illumination system of claim 1, wherein a deviation of the mixed white light generated by the illumination system relative to the respective target color temperatures is less than 0.006 where the target color temperature is in a color temperature range between 3000K and 6500K.

11. The illumination system of claim 1, further comprising:

a photosensitive detector configured to measure and provide feedback to the controller concerning a luminous flux generated by the at least four solid state light sources; and

a lightguide configured to provide light from the at least four solid state light sources to the photosensitive detector.

12. The illumination system of claim 1, comprising:

at least five solid state light sources, each solid state light source operable to emit light through the reflector; and

the controller programmed to generate the mixed white light by adjusting duty cycles of each of the at least five solid state light sources.

13. The illumination system of claim 1, wherein the controller is programmed to determine a monotonic function that includes a ratio of a duty cycle of a first light source included in the at least four solid state light sources and a duty cycle of a second light source included in the at least four solid state light sources across the continuous range of color temperatures.

14. The illumination system of claim 1, wherein the controller is programmed to determine a first duty cycle of a first of the at least solid state four light sources, and to determine a second duty cycle of a second of the at least four solid state light sources, and wherein a ratio of the first duty cycle to the second duty cycle provides a non-decreasing monotonic function across the continuous range of color temperatures.

15. The illumination system of claim 14, wherein the second duty cycle provides a non- increasing monotonic function of the second light source across the continuous range of color temperatures.

16. A method of providing illumination from a lighting source having at least four solid state light sources, comprising:

identifying a plurality of target color points based on respective target color

temperatures of each of the plurality of target color points; and

generating a mixed white light emitted by the lighting source by adjusting duty cycles of each of the at least four solid state light sources such that the duty cycles are adjusted monotonically relative to the respective target color temperatures across a continuous range of color temperatures.

17. The method of claim 16, wherein the continuous range of color temperatures includes a range from 3000K to 6500K.

18. The method of claim 16, further comprising:

receiving a target color temperature, a color point of at least one of the at least four light sources, and a peak wavelength value of a plurality of the at least four light sources,

receiving a spectral width value of at least one of the at least four solid state light sources; and

determining a transfer function including coefficients to provide a monotonic function of the duty cycles relative to color temperature based, at least in part, on the spectral width value and the peak wavelength value.

19. The method of claim 18, further comprising:

receiving the color point, the peak wavelength value, and the spectral width value as inputs to the transfer function.

20. The method of claim 16, wherein determining the respective duty cycles comprises:

determining a first duty cycle of a first light source included in the at least four solid state light sources; and

determining a second duty cycle of a second light source included in the at least four solid state light sources, wherein a ratio of the first duty cycle to the second duty cycle provides a non-decreasing monotonic function across the continuous range of color temperatures.

21. The method of claim 20, wherein determining the second duty cycle comprises:

determining a non-increasing monotonic function of the second duty cycle across the continuous range of color temperatures.

22. A computer readable medium encoded with a program for execution on a processor, the program, when executed on the processor performing a method of providing illumination from a lighting source having at least four solid state light sources, the method comprising acts of: identifying a plurality of target color points based on respective target color

temperatures of each of the plurality of target color points; and

23. The computer readable medium of claim 22, the method further comprising:

24. The computer readable medium of claim 22, the method further comprising:

receiving a target color temperature, a color point of at least one of the at least four light sources, and a peak wavelength value of a plurality of the at least four light sources;