Patent Publication Number: US-9900955-B1

Title: Luminaire having an adjustable color temperature of emitted light and related methods

Description:
This application claims the benefit of U.S. Provisional Patent Application No. 62/275,594, filed Jan. 6, 2016, the disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This application relates to the lighting arts and, in particular, an adjustable luminaire. 
     BACKGROUND 
     Luminaires or lighting fixtures are used for providing artificial light where needed, such as in buildings or outdoor areas. A typical luminaire may include a plurality of light emitting diode (LED) arrays in order to provide different color temperatures of emitted light. In such a scenario, each LED array provides light of a specific temperature (e.g., 2200 k, 2700 k, and/or 5000 k). Each array is typically driven by a designated LED driver and related circuitry and the emitted light is combined in order to provide a desired color temperature of emitted light. 
     It would be beneficial to have an improved luminaire that provides the ability to adjust the color temperature of emitted light utilizing at least one less LED driver than LED arrays. It would be further beneficial if the luminaire were capable of efficiently combining color temperatures of light emitted from different LED arrays even under dimming conditions without creating unwanted noise. The luminaire would allow for smaller packaging and could be adjusted in a variety of manners in order to achieve the desired objectives of tuned lighting. Related improvements are also proposed. 
     SUMMARY OF THE INVENTION 
     In accordance with the purposes and benefits described herein, a luminaire having an adjustable color temperature of emitted light is provided. The luminaire may be broadly described as including an input device for receiving an input indicative of a desired color temperature of emitted light, first, second and third LED arrays each array having a different color temperature, a first LED driver for driving one of the first and third LED arrays, a second LED driver for driving the second LED array, an LED array selector for selecting one of the first and third LED arrays to be driven by the first LED driver dependent upon the input, and a processor for determining which of the first and the third LED arrays to select based on the input and controlling the LED array selector and the second LED driver dependent upon the input. 
     In still another possible embodiment, the processor dims at least one of the first, second, and third LED arrays so the combined color temperature of light emitted from the first, second, and third LED arrays is substantially equal to the desired color temperature of emitted light. 
     In one other possible embodiment, the processor utilizes analog dimming above a predetermined noise threshold voltage and pulse width modulation dimming at or below the predetermined noise threshold voltage. In yet another, the analog dimming is maintained at a constant level substantially equal to the predetermined noise level voltage and pulse width modulation dimming is utilized to control dimming at or below the predetermined noise level voltage by varying the duty cycle. 
     In still another possible embodiment, the color temperature of the first LED array is 2200K, the color temperature of the second LED array is 2700K, and the color temperature of the third LED array is 5000K. In this embodiment, the processor may utilize analog dimming above a predetermined noise threshold voltage and pulse width modulation dimming below the predetermined noise threshold voltage. In another, the analog dimming may be maintained at a constant level substantially equal to the predetermined noise level voltage and pulse width modulation dimming is utilized to control dimming below the predetermined noise level voltage by varying the duty cycle. 
     In accordance with still yet another possible embodiment, a luminaire having an adjustable color temperature of emitted light is provided. The luminaire may be broadly described as including an input device for receiving an input indicative of a desired color temperature of emitted light, at least three LED arrays each array having different color temperatures, at least two LED drivers for driving at least one of the at least three LED arrays, at least one LED array selector for selectively driving two of the at least three LED arrays dependent upon the input, and a processor for determining which of the at least three LED arrays to drive based on the input and controlling the at least one LED array selector and the at least two LED drivers dependent upon the input. 
     In accordance with the purposes and benefits described herein, a method is provided of adjusting a color temperature of light emitted from a luminaire having first, second and third LED arrays, each array having a different color temperature. The method may be broadly described as comprising the steps of: receiving an input indicative of a desired color temperature of light emitted from the luminaire; processing the input and providing signals to first and second LED drivers, and an LED array selector dependent upon the input; and driving at least one of the first, second and third LED arrays utilizing at least one of the first LED driver and the second LED driver according to the signals so the combined color temperatures of light emitted from the at least one of the first, second and third LED arrays is substantially the same as the desired color temperature of light emitted from the luminaire. 
     In another possible embodiment, the step of driving at least one of the first, second and third LED arrays includes driving one of the first, second and third LED arrays with the first LED driver when the desired color temperature of light emitted from the luminaire is equal to the color temperature of light emitted from the one of the first, second and third LED arrays. 
     In yet another possible embodiment, the step of driving at least one of the first, second and third LED arrays includes driving the first LED array with the first LED driver and the second LED array with the second LED driver when the desired color temperature of light emitted from the luminaire is between the color temperature of the first LED array and the color temperature of the second LED array. 
     In one other possible embodiment, the method further includes the step of dimming at least one of the first LED array and the second LED array so the combined color temperatures of the light emitted from the first LED array and the light emitted from the second LED array are substantially equal to the desired color temperature of light emitted from the luminaire. 
     In still another possible embodiment, the step of dimming utilizes analog dimming above a predetermined noise threshold voltage and pulse width modulation dimming below the predetermined noise threshold voltage. In another, the analog dimming is maintained at a constant level substantially equal to the predetermined noise level voltage and pulse width modulation dimming is utilized to control dimming below the predetermined noise level voltage by varying the duty cycle. 
     In still another, the step of selectively driving at least one of the first, second and third LED arrays includes driving the third LED array with the first LED driver and the second LED array with the second LED driver when the desired color temperature of light emitted from the luminaire is between the color temperature of the second LED array and the color temperature of the third LED array. 
     In still another possible embodiment, the method further includes the step of dimming at least one of the second LED array and the third LED array so the combined color temperatures of the light emitted from the second LED array and the light emitted from the third LED array are substantially equal to the desired color temperature of light emitted from the luminaire. 
     In yet another possible embodiment, the step of dimming utilizes analog dimming above a predetermined noise threshold voltage and pulse width modulation dimming below the predetermined noise threshold voltage. In still another, the analog dimming is maintained at a constant level substantially equal to the predetermined noise level voltage and pulse width modulation dimming is utilized to control dimming below the predetermined noise level voltage by varying the duty cycle. 
     In accordance with another aspect of the invention, a method is provided of adjusting a color temperature of light emitted from a luminaire. The method comprises the steps of providing first, second and third LED arrays having different color temperatures, providing first and second LED drivers, and selectively driving at least one of the first, second and third LED arrays utilizing at least one of the first LED driver and the second LED driver dependent upon a desired color temperature of the luminaire. 
     In one other possible embodiment, the method further includes the step of dimming at least one of the first, second, and third LED arrays so the combined color temperature of the light emitted from the first, second, and third LED arrays is substantially equal to the desired color temperature. 
     In another possible embodiment, the step of dimming utilizes analog dimming above a predetermined noise threshold voltage and pulse width modulation dimming below the predetermined noise threshold voltage. 
     In the following description, there are shown and described several embodiments of a luminaire having an adjustable color temperature of emitted light, and related methods of adjusting the color temperature of light emitted from the luminaire. As it should be realized, the invention is capable of other, different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the invention as set forth and described in the following claims. For example, the luminaire is scalable to accommodate any number of LED arrays having different color temperatures. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawing figures incorporated herein and forming a part of the specification, illustrate several aspects of the vehicle having an auxiliary duct pivotally attached to a console and together with the description serve to explain certain principles thereof. In the drawing figures: 
         FIG. 1  is a perspective view of a luminaire; 
         FIG. 2  is a cross sectional plan view of the luminaire; 
         FIG. 3  is a block schematic diagram of the luminaire; 
         FIG. 4  is a block schematic diagram of an alternate luminaire having four LED arrays having different color temperatures; and 
         FIG. 5  is a graphical representation of analog and PWM dimming levels. 
     
    
    
     Reference will now be made in detail to the present preferred embodiments of the luminaire and related methods, examples of which are illustrated in the accompanying drawing figures. 
     DETAILED DESCRIPTION 
     Reference is now made to  FIG. 1  which illustrates one embodiment of a luminaire  10 . In the described embodiment, the luminaire  10  is designed for mounting on a ceiling. However, any form of luminaire utilizing multiple LED arrays having different color temperatures may utilize the present invention. While three LED arrays are utilized in the described embodiment, the invention is scalable to accommodate any number of LED arrays having different color temperatures which allows the luminaire to more closely approximate a blackbody curve for white light. 
     As shown in  FIG. 2 , the luminaire  10  includes wires  12  for connecting to residential power or an alternate power source. The wires  12  can be spliced directly to residential power or electrically connected through a connector. A transformer  14  steps the AC line voltage down to 24 volt DC which is further stepped down by a synchronous DC-DC converter  15  as shown in  FIG. 3 . In the described embodiment, the DC-DC converter  15  is a Texas Instruments® LM43601 regulator capable of driving up to 1 A of load current from an input voltage ranging from 3.5 V to 36 V (42 V transient). The regulator  15  is mounted on an LED board  16  shown in  FIG. 2 . The LED board  16  in turn is mounted in contact with a heat sink  17 . 
     The 24 volt DC and 3.3 volt DC signals are used throughout the LED board  16  to drive first, second and third LED arrays  18 ,  20 ,  22 , and to adjust a color temperature of light emitted from the luminaire  10 . In the described embodiment, the first LED array  18  (or LED ring) includes four strings of twelve LEDs. Each of the LEDs in the first LED array have a color temperature of 2200K. The second LED array  20  and third LED array  22  each also include four strings of twelve LEDs. Each of the LEDs in the second LED array  20  have a color temperature of 2700K and each of the LEDs in the third LED array  22  have a color temperature of 5000K. Depending on how the first, second and third LED arrays are controlled/driven, the color temperature of the combined light emitted from the luminaire  10  can be adjusted from 2200K through and including 5000K. In other words, the color temperature can be 2200K, 5000K, or any number therebetween (e.g., 2237K). In addition, the LED arrays may have other color temperatures (e.g., 4200K, 4000K, 3200K, 3000K, etc.) or may include combinations of LEDs having different temperatures. 
     As further shown in  FIG. 3 , a processor  24 , powered by converter  15 , is mounted on the LED board  16  receives an input signal from an input device  26 . In the described embodiment, the processor  24  is a Freescale Semiconductor Inc. MK12DX256VLF5 32-bit microcontroller and the input device  26  is a WIFI radio. In alternate embodiments, the input device  26  could be any type of device (e.g., an IR receiver, a light sensor, and/or an occupancy sensor) capable of receiving a user input indicative of a desired color temperature of the light emitted from the luminaire  10 . The device could receive signals via the WIFI radio from a wall mounted control, a hand-held control, and/or a smartphone. Typically, the input device provides up/down arrows for inputting the desired color temperature, however, any device capable of indicating a desired temperature is sufficient. The input device  26  may also be directly wired to the luminaire  10 . 
     Algorithms within the processor  24  determine whether a first LED driver  28  and a second LED driver  30  are used to drive the first, second and/or third LED arrays  18 ,  20 ,  22 . The processor  24  outputs a control signal to the first LED driver  28  which outputs a gate drive signal for driving the second LED array  20 . In the described embodiment, the first and second LED drivers  28 ,  30  each include a Linear Technology® LT3756 DC/DC controller designed to operate as a constant-current source for driving high current LEDs, an inductor, and a switch. The inductors are Coilcraft® LPS6235 series low profile shielded power inductors and the switches are ON Semiconductor NTTFS5826NL power MOSFETs. A switch  32  controlled by the processor  24  turns the second LED array  20  on/off. In the described embodiment, the switch  32  is an Infineon® BSZ100N06LS3 G power transistor. 
     The processor  24  further outputs a control signal to the second LED driver  30  which outputs a gate drive signal for selectively driving the first LED array  18  or the third LED array  22 . In the described embodiment, a switch  34  controlled by an LED array selector  36  turns the first LED array  18  on/off and a second switch  38  controlled by the LED array selector turns the third LED array  22  on/off. In the described embodiment, the switches  34  and  38  are both Infineon® BSZ100N06LS3 G power transistors and the LED array selector  36  is a Texas Instruments® UCC27524DGNR dual, high-speed, low-side power MOSFET driver. 
     Determination as to whether the first LED array  18  or the third LED array  22  is operated depends on the input signal from the input device  26 . If the desired color temperature of light emitted from the luminaire  10  is between 2200K and 2700K, the first LED array  18  and the second LED array  20  are utilized to create a combination of light which approximates the blackbody curve for white light and substantially equals the desired color temperature. Similarly, if the desired color temperature of light emitted from the luminaire  10  is between 2700K and 5000K, the second LED array  20  and the third LED array  22  are utilized to create a combination of light substantially equal to the desired color temperature. In the event the desired color temperature is the same as the color temperature of one of the three LED arrays, then only one LED driver is utilized and only one LED array is turned on. 
     As indicated above, the LED array selector  36  is utilized to selectively drive one of the first LED array  18  and the third LED array  22  with the second LED driver  30  as shown in  FIG. 3 . In the described embodiment, the LED array selector  36  receives controls signals from the processor  24  which determines whether the LED array selector  36  passes an output signal from the second LED driver  30  to the switch  34  or the second switch  38  in order to turn the first LED array  18  or the third LED array  22  on/off respectively. 
     As shown in  FIG. 4 , the above-described circuit can be expanded to accommodate any number of LED arrays. As shown, the alternate circuit includes three LED arrays, as in the previously described circuit, and a fourth LED array  40 . In order to select between the second LED array  20  and the fourth LED array  40 , an additional LED array selector  42  and switch  44  are added to the circuit described in  FIG. 3 . The additional LED array selector  42  and switch  44  operate the same as the LED array selector  36  and switches  34  and  38  described above except the new LED array selector and switch control whether the second LED array  20  or the fourth LED array  40  are operated. 
     In order to accommodate the efficient combining of color temperatures of light emitted from different LED arrays under dimming conditions and without creating unwanted noise, a combination of analog and pulse width modulation (PWM) dimming is utilized. This provides for an improved dimming ratio than either analog or PWM dimming can achieve individually. More specifically, analog dimming has a useful range of 10:1 and is limited by noise in the system below a certain threshold. 
     As shown in  FIG. 5 , as an analog signal level  50  decreases during dimming over a period of 1.8 seconds, the signal level approaches a noise level threshold  52  at or near 250 millivolts. It should be noted that the LEDs turn off at around 100 millivolts. Near the 250 millivolt level, resolution is lost due to the noise. However, PWM dimming has a useful range of 3000-5000:1 which is limited by LED driver response time. By combining analog and PWM dimming, a dimming ratio of 50000:1 can be approached. While single color systems are unlikely to need a 50000:1 dimming ratio, the added dimming capability allows for smoother color temperature transitions at low lumen output when mixing colors as in the present embodiment. The line  50  in the plot shown in  FIG. 5  represents an analog signal level decreasing linearly. At the predefined noise threshold level  52 , the analog signal level is held constant and PWM dimming is initiated and utilized and further dimming made by reducing the duty cycle as represented by line  54 . 
     In the described embodiment, dimming is utilized to better approximate the desired color temperature. In other words, at least one of the first LED array  18  or the third LED array  22 , and the second LED array  20  are dimmed so the combined color temperatures of the light emitted from the first LED array or the third LED array, and the light emitted from the second LED array are substantially equal to the desired color temperature. The processor  24  utilizes both analog dimming above a predetermined noise threshold voltage and PWM dimming below the predetermined noise threshold voltage. More specifically, the analog dimming is maintained at a constant level substantially equal to the predetermined noise level voltage and PWM dimming is utilized to control dimming below the predetermined noise level voltage by varying the duty cycle. 
     The foregoing has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Obvious modifications and variations are possible in light of the above teachings. All such modifications and variations are within the scope of the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.