The assignee for this patent, patent number 8649004, is
Reporters obtained the following quote from the background information supplied by the inventors: "A white light-emitting LED luminary is described in WO 02/099333 A1. The LED luminary incorporates an array of red, green and blue emitting LEDs and a feedback arrangement for maintaining a desired color balance. The feedback arrangement includes photodiodes positioned and enabled to separately measure the light output of each RGB color component. In one embodiment, a single photodiode or array of photodiodes is positioned to intercept reflected light from a partially reflecting element placed in the path of the combined output of the LED array. Individual colors are measured sequentially by pulsing the LEDs and photodiodes or by the use of color filters. Interference filters are normally used for high accurate color control. The angle dependency of the transmission wavelength of interference filters may cause problems during operation."
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "It is an object of the invention to provide an improved and cost-effective light sensor.
"It is a further object of the invention to provide a lighting device with such an improved and cost-effective light sensor.
"It is another object of the invention to provide a method of controlling a lighting device.
"One object of the present invention is achieved by a light sensor comprising a light diffuser, an optical non-transparent housing having at least one window, at least one interference filter and at least two photo sensors, the light diffuser being arranged in such a way that light from outside the optical non-transparent housing has to pass the light diffuser so as to enter the interior of the optical non-transparent housing via the window, the interference filter and the at least two photo sensors being arranged in the interior of the optical non-transparent housing, said interference filter being arranged between the window and the at least two photo sensors.
"The combination of the optical diffuser and the window results in an approximately Lambertian radiator with a Lambertian ray pattern according to Lambert's cosine law with respect to the surface of the interference filter. The window preferably has a smaller width than the photo sensor. More preferably, the width of the window is smaller than 1/10 of the width of the photo sensor. The optical diffuser can be arranged anywhere between a light source emitting light to be detected by the light sensor and the window. In addition, the inner surface of the optical non-transparent housing should be light-absorbing, e.g. by roughening the surface or by providing a light-absorbing layer reducing the reflected light in a sufficient way to minimize signal noise due to reflected light in the interior of the non-transparent housing. The Lambertian ray pattern is used in combination with the interference filter or interference filters and the photo sensors, such as, for example, photodiodes for detecting the emission characteristics and especially the color characteristics of incident light. The color characteristics of the incident light are determined e.g. by detecting the relative intensity of the light passing through the window in at least two different wavelength ranges.
"In one embodiment of a light sensor according to the invention, the light sensor comprises an optical non-transparent housing with one interference filter. In combination with the angular dependence of the transmission wavelength of the interference filter, the Lambertian ray pattern is used to detect the relative intensity of the light passing through the window in at least two different wavelength ranges. The interference filter is preferably attached to the photo sensors. Taking a circular hole as a window, the first photo sensor preferably has an essentially circular shape and receives light from the circular hole emitted at certain solid angles corresponding to a first transmission band of the interference filter and the second photo sensor having an essentially annular shape circumventing the first photo sensor. The second photo sensor receives light from the circular hole emitted at different solid angles corresponding to a second optical transmission band of the interference filter. A spacer can be arranged between the first and the second photo sensor in order to improve the separation between the optical transmission bands. This configuration has the advantage that only one interference filter is needed, which reduces the costs of the light sensor. The circularly symmetrical arrangement of the photo sensors allows receiving a maximum signal strength. Other arrangements are possible, such as patches of photo sensors covering defined ranges of angles of incidence with respect to the normal of the layer defined by the surface of the interference filter.
"In a further embodiment of a light sensor according to the invention, the light sensor comprises an optical non-transparent housing having at least two windows, at least two lenses and at least two interference filters, the windows and lenses being arranged as collimators in the optical non-transparent housing and the at least two interference filters having a maximum transmission at different wavelength ranges. The windows are preferably circularly shaped holes, with each hole being arranged in the focal point of a lens. Diffuse light passing through one of the holes has to pass through the corresponding lens and reaches the corresponding interference filter as a parallel beam. Only light of a certain wavelength range depending on the interference filter passes the interference filter, which results in a precise measurement of the intensity of light in a rather narrow wavelength range by means of the corresponding photo sensor. The parallel beam of light prevents broadening of the transmission wavelength range of the interference filter due to light at different angles of incidence. The lens used in this arrangement may comprise a first material having a refractive index n1 and a second material having a refractive index n2, in which n2 is larger than n1, the first material being arranged as a plane-parallel plate with at least two recesses perpendicular to the plane-parallel plate of the first material, the recesses being filled with the second material. The recesses preferably but not necessarily have a circularly symmetric cross-section parallel to the plate of the first material. The shape of the cross-section of the recesses perpendicular to the plate of the first material is arranged in such a way that the focal point of the lens formed by the combined structure of the second material filled in the recesses in combination with the plate of the first material is at the location where the windows (for example, circularly shaped holes) are arranged.
"Another object of the present invention is achieved by a lighting device comprising a light sensor as described above, a light source with adaptable color and control electronics, the at least two photo sensors of the light sensor being designed to supply an electric control signal after detecting light passing the at least one interference filter, the control electronics being designed to adapt the color of the light source on the basis of the electric control signal detected by the photo sensors.
"The color of the light source is e.g. determined by detecting the relative intensity of the light passing through the window in at least two different wavelength ranges. The light source may be either a single light emitter with a controllable color of the emitted light or an array of light emitters with either a controllable color of the emitted light or at least two light emitters emitting light in different colors. The inner surface of the optical non-transparent housing of the light sensor should be light-absorbing, e.g. by roughening the surface or by providing a light-absorbing layer reducing the reflected light in a sufficient way so as to minimize signal noise due to reflected light in the interior of the non-transparent housing. Depending on the amount of light passing through the window, the signal strength can be reduced by adapting the size of the window and/or the size of the photo sensors, or it can be enhanced by using an array of windows wherein each window has dedicated photo sensors as described above. The windows and the dedicated photo sensors may be arranged in optically separated cells within the interior of the optical non-transparent housing, wherein 'optically separated' is understood to mean that light entering the interior of the optical non-transparent housing via one window is only detected by the dedicated photo sensors. Alternatively, a plurality of light sensors may be used in one lighting device. The control electronics may comprise means such as a processor with storage means and adapted software, or an ASIC to analyze the detected data of the different cells or photo sensors in order to reduce measurement errors.
"In another embodiment of a lighting device according to the invention, LEDs are used as light sources. The LEDs have different colors such as e.g. red and blue. The intensity of each LED can be individually controlled by means of the control electronics in accordance with the control signals detected by the photo sensors. Control of the intensity of the LEDs allows spanning a sub-space of color space by means of the linear combination of the light emitted by the LEDs. Further well-known combinations of LEDs that can be used are, for example, the combination of a red, green and blue (RGB) LED or a red, green, blue and amber LED. In general, control of the light source can be used to change the color of the lighting device and/or to compensate changes of colors of the lighting device due to internal and external factors. Internal and external factors are, for example, temperature, the electric current driving the LED and aging being especially but not exclusively relevant for LEDs.
"In a further embodiment of a lighting device according to the invention, the light source comprises at least two LEDs and a luminescence converter. The luminescence converter may be a phosphor powder distributed in a silicon or epoxy resin matrix, wherein 'phosphor powder' is understood to mean one or more phosphor materials converting light of a first wavelength, which may be emitted by the light source, to light of a second wavelength. Special types of luminescence converters are monolithic luminescence converters such as ceramic luminescence converters as disclosed in WO 2006/087660, herein incorporated by reference, or glass with dissolved phosphor particles. The luminescence converter is at least partly used as a diffuser and/or optical light guide. In a special embodiment, the luminescence converter is a monolithic luminescence converter plate with at least one recess, the light sensor being placed in the recess and the window being in contact with the monolithic luminescence converter. Contact between the monolithic luminescence converter and the window may be either direct or indirect, wherein 'direct' is understood to mean that there is no intermediate layer between the monolithic luminescence converter and the window, and 'indirect' is understood to mean that there is an intermediate layer between the monolithic luminescence converter and the window. The intermediate layer may be, for example, an antireflection layer or an optical matching layer decreasing the probability of total reflection at the surface of the monolithic luminescence converter facing the window of the light sensor. The LEDs may also be in direct or indirect contact with the monolithic luminescence converter emitting light in this converter. The wavelength of at least a part of the light entering the monolithic luminescence converter is converted to a different wavelength. Furthermore, the light is scattered at the grain boundaries of the ceramic material if the monolithic luminescence converter is a monolithic ceramic luminescence converter working as an optical diffuser. In addition, the light within the monolithic luminescence converter is reflected at its surface due to the higher refractive index of the monolithic luminescence converter in comparison with air guiding the light to the location where the window of the light sensor is in contact with the monolithic luminescence converter. The part of the monolithic luminescence converter where the light sensor is placed can be covered with a reflective layer or coating. The reflective layer or coating can be used to shield the light sensor from ambient light and to enhance the amount of light that can enter the light sensor via the window.
"The lighting device according to the present invention may be used in one or more of the following applications: Office-lighting systems, Household application systems, Shop-lighting systems, Home-lighting systems, Accent-lighting systems, Spot-lighting systems, Theater-lighting systems, Fiber-optics application systems, Projection systems, Self-lit display systems, Pixelated display systems, Segmented display systems, Warning-sign systems, Medical lighting application systems, Indicator-sign systems, Decorative lighting systems, Portable systems, Automotive applications, Greenhouse lighting systems.
"A further object of the invention is achieved by means of a method of controlling a lighting device, the method comprising the steps of: providing light having a Lambertian ray pattern; detecting the intensity of the light in at least two wavelength ranges by using the optical characteristics of the Lambertian ray pattern; supplying electric control signals based on the detected intensities, and controlling the lighting device by means of the electric control signals.
"Diffusing light of a light source by means of a diffuser and providing a window in an optically non-transparent housing may provide the Lambertian ray pattern of the light. Providing photo sensors in combination with at least one interference filter arranged between the window in the optically non-transparent housing and the photo sensors may be used to detect the relative intensity of the light source in at least two wavelength ranges by using the optical characteristics of the Lambertian ray pattern. The electric control signals may be supplied by means of the photo sensors."
For more information, see this patent: Schulz, Volkmar; Martiny, Christoph; Meijer,
Keywords for this news article include: Electronics,
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