Patent Publication Number: US-11399420-B2

Title: Lighting systems for general illumination and disinfection

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/850,760, filed Apr. 16, 2020, which is a continuation-in-part of U.S. Ser. No. 16/750,031, filed on Jan. 23, 2020, which is itself a continuation of U.S. Ser. No. 16/425,083, filed on May 29, 2019, now U.S. Pat. No. 10,582,586, which claimed priority to U.S. Serial Nos. 62/811,551 (filed Feb. 28, 2019) and 62/677,405 (filed May 29, 2018). The entire disclosures of all of the foregoing documents are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to lighting systems, and in various embodiments to systems for providing mixed light for illumination and disinfection purposes. 
     BACKGROUND 
     It is known that certain wavelength ranges of light, particularly ultraviolet (UV) light, are germicidal—i.e., capable of killing or inactivating pathogens such as bacteria and viruses, rendering them incapable of causing disease. Illumination devices emitting germicidal light are frequently used to decontaminate medical tools and environmental surfaces. UV radiation is dangerous to humans, and some wavelength bands are more dangerous than others. As a result, broadband germicidal UV applications are typically deployed in oven-like devices that receive items to be decontaminated and are closed when the radiation is activated, thereby shielding personnel from harm. Although automated UV-based room-decontamination systems have been developed, these generally are not used when people are present. See, e.g., Livingston et al., “Efficacy of an ultraviolet-A lighting system for continuous decontamination of health care-associated pathogens on surfaces,”  Am. J. Infection Control,  48:337-339 (2020). Unfortunately, recontamination can occur quickly following device operation once people return and resume their activities. 
     The most effective germicidal wavelength band, UV-C (100-280 nm), is also the most dangerous to humans. The UV-A band (315-400 nm), on the other hand, can be safe for use in limited doses when people are present, and is known to have antimicrobial activity. Accordingly, it is possible to safely integrate UV-A lighting with general illumination, but the lighting sources used for these different wavelength ranges are different. Their outputs must be combined in a manner that preserves the quality of ambient light for affected personnel while ensuring safety. 
     SUMMARY 
     An increasing number of light fixtures utilize LEDs as light sources due to their lower energy consumption, smaller size, improved robustness, and longer operational lifetime relative to conventional filament-based light sources. Conventional LEDs emit light at a particular wavelength, ranging from, for example, red to UV light. However, for purposes of general illumination, the monochromatic emitted light by LEDs must be converted to broad-spectrum white light. 
     Embodiments of the present invention combine UV-A and white light with an adjustable CCT value so that any adverse effects from the the UV-A radiation are mitigated—that is, tunable adjustments to the output of the non-UV LEDs, or to all of the LEDs, result in an overall mixed output conforming to a target CCT value. In one embodiment, the LED illumination device employs an LED array having multiple LEDs that can be controlled individually or in a group to generate white light having a tunable CCT value within a range. Optionally, each of the LEDs may be disposed within a “cup-shaped” (e.g., parabolic) reflector for reducing “crosstalk” interactions between the light emitted from an LED and the photo-luminescent material(s) disposed above a neighboring LED. In addition, the reflector may be made of a high-reflectivity material so as to redirect upward light from the respective LED, thereby achieving at least partial collimation of the beam. 
     In various embodiments, the LEDs and/or photo-luminescent material(s) are encapsulated within a waveguide material made of, e.g., silicone. Light emitted from the LEDs, including unconverted light and light converted by the photo-luminescent material(s), can be mixed in a mixing region inside the waveguide and then directed to an output region for outputting white light for illumination. The illumination device may also include control circuitry for varying a parameter (e.g., the amplitude and/or duty cycle of the applied current or voltage) associated with each LED (or, in some embodiments, each group of the LEDs), thereby adjusting the CCT value of the mixed light to a target value. 
     Accordingly, in one aspect, the invention relates to a lighting device producing white light having a target CCT value and UV-A radiation. In various embodiments, the device comprises a plurality of red LEDs emitting red light having a wavelength between approximately 600 nm and approximately 670 nm, a plurality of blue LEDs emitting blue light having a wavelength between approximately 440 nm and approximately 485 nm, and a plurality of UV-A LEDs emitting UV radiation having a wavelength between approximately 315 nm and approximately 420; at least one photo-luminescent material for shifting a CCT value of at least one of (a) the red LEDs, (b) the blue LEDs or (c) the UV-A LEDs; and a waveguide material having (i) a mixing region for mixing the shifted and any unshifted light so as to generate white light having the target CCT value and (ii) an output region for outputting the white light. The red LEDs may have an emission peak at 630 nm, the blue LEDs have an emission peak at 450 nm, and the UV-A LEDs have an emission peak at 395 nm. 
     In some embodiments, the device also includes control circuitry for adjusting a parameter associated with at least one of the red LEDs, the blue LEDs or the UV-A LEDs so as to change the target CCT value of the generated white light. For example, the parameter may comprise at least one of an amplitude or a duty cycle of a current or a voltage associated with the red LEDs, the blue LEDs and/or the UV-A LEDs. 
     The control circuitry may be configured to adjust the parameter of each red LED, blue LED and UV-A LED to maintain the target CCT value while changing the intensity of the UV-A light. In some embodiments, the LEDs comprises a first group of the red LEDs and the UV-A LEDs electrically coupled to one another, a second group of the blue LEDs and the UV-A LEDs electrically coupled to one another, and a third group of the UV-A LEDs electrically coupled to one another; the control circuitry may be configured to adjust each of the groups individually. The UV-A LEDs in the third group may emit light at a wavelength having a lower interaction with the photo-luminescent material than the wavelengths emitted by the UV-A LEDs in the first group or the UV-A LEDs in the second group. Alternatively or in addition, the UV-A LEDs in the first group may emit light at a wavelength having a higher interaction with the photo-luminescent material than the UV-A LEDs in the second group. The photo-luminescent material may comprise at least one of a phosphor, a quantum dot material or a fluorescent dye. 
     In some embodiments, the lighting device further comprises a plurality of cup-shaped reflectors for at least partial collimation of light emitted from the LEDs, wherein each reflector has a top aperture and a bottom aperture and the bottom aperture has one of the LEDs disposed therein. At least one of the reflectors may be a parabolic reflector, and the respective LED disposed therein may be located at or near the focus of the parabolic reflector. The reflectors may comprise or consist essentially of silicone. 
     The lighting device may include an encapsulant material filled in a cavity space above one of the plurality of LEDs and surrounded by the respective reflector. In some embodiments, the lighting device further comprises a circuit board for mounting the LEDs thereon, and if desired, the lighting device may include a heat-dissipation structure thermally coupled to the circuit board for dissipating heat generated by the plurality of LEDs. In some embodiments, the lighting device further comprises at least one reflector located in the mixing region of the waveguide for promoting mixing of light. The waveguide material may comprise or consist essentially of silicone. The waveguide material may encapsulate at least one LED. 
     In another aspect, the invention relates to a lighting system comprising, in various embodiments, the lighting system includes a plurality of devices for producing white light having a target CCT value and UV-A radiation. Each of the devices may comprise a plurality of LEDs emitting visible light and a plurality of UV-A LEDs emitting UV radiation having a wavelength between approximately 315 nm and approximately 420; at least one photo-luminescent material for shifting a CCT value of at least some of the LEDs; a waveguide material having (i) a mixing region for mixing the shifted and any unshifted light and (ii) an output region for outputting the light; and a controller configured to operate the plurality of devices in (a) a normal mode, powering the LEDs, so as to generate white light having the target CCT value while emitting UV-A light or (b) in a boost mode, powering fewer than all of the LEDs emitting visible light and powering at least a majority of the UV-A LEDs at high intensity. In the normal mode, the UV-A light may have an intensity that is safe for human exposure and in the boost boost mode the intensity may exceed the intensity that is safe for human exposure. In the the boost mode, LEDs emitting red light may be operated to indicate a risk of harmful radiation. The plurality of LEDs emitting visible light may comprise (i) a plurality of red LEDs emitting red light having a wavelength between approximately 600 nm and approximately 670 nm and (ii) a plurality of blue LEDs emitting blue light having a wavelength between approximately 440 nm and approximately 485 nm. 
     The term “color” is used herein to denote the monochromatic or peak wavelength (or wavelengths) of light emitted by one or more LEDs. In addition, the term “uniform,” as used herein, refers to a light intensity distribution whose lower and upper intensity limits are within a factor of four, preferably within a factor of two of each other. As used herein, the terms “approximately,” “roughly,” and “substantially” mean±10%, and in some embodiments, ±5%. Reference throughout this specification to “one example,” “an example,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present technology. Thus, the occurrences of the phrases “in one example,” “in an example,” “one embodiment,” or “an embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, routines, steps, or characteristics may be combined in any suitable manner in one or more examples of the technology. The headings provided herein are for convenience only and are not intended to limit or interpret the scope or meaning of the claimed technology. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, with an emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which: 
         FIGS. 1A and 1B  depict a top view and a bottom view, respectively, of an example illumination system in accordance with various embodiments; 
         FIGS. 1C and 1D  depict exemplary configurations of the LEDs in an illumination system in accordance with various embodiments; 
         FIG. 2A  schematically depicts an exemplary three-dimensional configuration of an illumination system in accordance with various embodiments; 
         FIG. 2B  depicts a spatial arrangement of LEDs and associated conversion layers for converting the wavelength of at least a portion of the LED light in accordance with various embodiments; 
         FIGS. 2C and 2D  depict LED arrays including various combinations of different types of LEDs in accordance with various embodiments; 
         FIG. 2E  depicts a conversion layer including multiple regions in accordance with various embodiments; 
         FIGS. 3A and 3B  depict an implementation of reflectors surrounding the LEDs in an illumination system in accordance with various embodiments; 
         FIGS. 4A and 4B  depict exemplary color coordinates of the light emitted from a warm white LED, a cool white LED, and a red LED in the CIE 1931 color space in accordance with various embodiments; 
         FIG. 4C  depicts shifts of color coordinates in the color space resulting from a waveguide/encapsulant material and one or more photo-luminescent materials in accordance with various embodiments; 
         FIG. 4D  depicts a green region and a yellow region in the CIE 1931 color space in accordance with various embodiments; and 
         FIG. 4E  depicts adjustments of the CCT value along the Black Body Curve (BBC) in accordance with various embodiments. 
         FIG. 5A  depicts an exemplary LED configuration including groups of red, blue, and UV-A LEDs combined in series. 
         FIG. 5B  depicts an exemplary LED configuration including groups of red and blue LEDs in one series and an adjacent series of UV-A LEDs. 
         FIG. 5C  depicts an exemplary LED configuration including red and blue LEDs and two types of UV-A LEDs. 
         FIGS. 6 and 7  graphically depict excitation and emission spectra for photo-luminescent materials useful in connection with embodiments of the invention. 
         FIG. 8  depicts a representative angular UV-A light distribution from a luminaire based on an embodiment of the present invention. 
         FIG. 9  illustrates the UV-A distribution over a room-size space of an array of luminaires as shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  conceptually illustrates an exemplary illumination system  100  including one or more strip lighting devices  102  in accordance herewith; each strip  102  has an array of multiple LEDs  104  mounted to a circuit board  106  (e.g., printed circuit board, PCB). Each of the LED groups  104  may include one or more LED dies for emitting light with the same or different characteristics (e.g., colors, powers and/or CCT values). The LEDs  104  may be electrically coupled, via the circuit board  106 , to connectors  108  mounted on each end of the circuit board  106 . The connectors  108  may then electrically couple the LEDs  104  to an external device  110  (e.g., another lighting device, a dimming device, a power supply, an “Internet of things” (IoT) device, or a combination thereof) such that the LEDs  104  may receive power from the external device  110  via the connectors  108  and emit light. 
     In some embodiments, the LEDs  104  are electrically coupled to control circuitry  112  in the strip lighting device(s)  102 . The control circuitry  112  may be configured to control operation of the LEDs  104  (e.g., by regulating the amplitude and/or duty cycle of the current and/or voltage applied to the LEDs  104 ), thereby regulating a characteristic (e.g., intensity or brightness) of the light emitted from the LEDs  104 . For example, the control circuitry  112  may adjust the brightness of individual LEDs using pulse width modulation (PWM). For example, the control circuitry  112  may rapidly turn individual LEDs on and off at a high frequency that is imperceptible to humans. In this example, the brightness of the individual LEDs  104  may be changed by adjusting the ratio of on-time to off-time within a particular cycle (sometimes referred to as a “duty cycle”). The higher the ratio of on-time to off-time, the brighter the LED. Conversely, lowering the ratio of on-time to off-time dims the LED. Thus, the duty cycle may positively correlate to the average flux of the LED being controlled. The control circuitry  112  may vary the ratio of on-time to off-time based on control signals received from the external device  110  via the connectors  108 . In one embodiment, the control circuitry  112  is implemented in circuitry that is external to the illumination system  100 . For example, circuitry in the external device  100  may be configured to regulate the current and/or voltage applied to the LEDs  104 , thereby directly controlling operations thereof. In this case, the control circuitry  112  may be omitted from the illumination system  100  altogether. 
     Generally, the LEDs  104 , control circuitry  112 , and/or the connectors  108  are all mounted to the circuit board  106 . For example, the circuit board  106  may include one or more conductors to electrically couple the components mounted thereto. In addition, the circuit board  106  may be flexible to enable the illumination system  100  to conform to uneven surfaces. Referring to  FIG. 1B , in some embodiments, the bottom surface of the circuit board  106  is connected to a heat dissipation structure  120  (e.g., a conventional heat sink) for dissipating heat generated by the LEDs  104 . 
     The strip lighting device(s)  102  in the illumination system  100  may have particular dimensions to enable a wide range of applications. For example, the lighting devices  102  may have a depth of no more than approximately 1 inch, a length of no more than approximately 25 inches, and a width of no more than approximately 4 inches. It should be appreciated that the strip lighting devices  102  may be constructed with other dimensions, and may be two-dimensional arrays of LED groups rather than one-dimensional strips. 
     In various embodiments, the LEDs  104  are separated by a distance (e.g., 25 millimeters (mm) or 3 mm). In addition, each of the LEDs  104  may be configured to emit light with the same or different characteristic (e.g., wavelength, CCT value, etc.). In one embodiment, the strip lighting devices  102  include one or more groups of LEDs, each group including at least one red LED  104 - 1  having a wavelength between approximately 600 nm and approximately 670 nm, one “warm” white LED  104 - 2  emitting white light having a CCT value between approximately 1800K and approximately 2700K, and one “cool” white LED  104 - 3  emitting white light having a CCT value between approximately 3000K and approximately 6500K. The group of LEDs  104 - 1 ,  104 - 2 ,  104 - 3  may be aligned consecutively on the same strip lighting device  102  (as depicted in  FIG. 1A ) or in any suitable configurations for generating white light with an adjustable characteristic (e.g., a CCT value) as further described below. For example, referring to  FIG. 1C , the group of LEDs  104 - 1 ,  104 - 2 ,  104 - 3  may be disposed on the same column on consecutive strips  102  abutting one another. Alternatively, referring to  FIG. 1D , the two white LEDs  104 - 2 ,  104 - 3  may be disposed next to each other on the same strip  102  while the red LED  104 - 1  may be disposed next to one of the white LEDs  104 - 2 ,  104 - 3  but on a different strip. 
     The LEDs  104  may be operated individually or in a grouped manner. For example, each LED may be independently coupled to the control circuitry  112  such that the control circuitry  112  can separately control individual LEDs. Alternatively, some of the LEDs  104  may be wired together to allow the control circuitry  112  to control them as a single unit; different groups may or may not share one or more LEDs  104 . For example, as described above, the illumination device  100  may include multiple groups of LEDs, each group including at least one red LED  104 - 1 , one warm white LED  104 - 2 , and one cool white LED  104 - 3 . In one embodiment, the LEDs  104 - 1 ,  104 - 2 ,  104 - 3  in each group are electrically coupled such that the control circuitry  112  can control the LEDs  104 - 1 ,  104 - 2 ,  104 - 3  equivalently. In another embodiment, the red LEDs  104 - 1  in at least some groups are electrically coupled together; this allows the control circuitry  112  to control equivalently all red LEDs  104 - 1  that are electrically coupled. Similarly, the warm white LEDs  104 - 2  in at least some groups may be electrically coupled together, and the cool white LEDs  104 - 3  in at least some groups are electrically coupled together. This way, the groups of warm white LEDs  104 - 2  and cool white LEDs  104 - 3  may be separately controlled by the control circuitry  112  in a group manner. 
     Referring to  FIG. 2A , in some embodiments, light emitted from the LEDs  104  travels through the space of a surrounding cavity  202  and is incident upon one or more conversion layers  204  that include one or more photo-luminescent materials (e.g., phosphors, quantum dot materials, etc.) for converting the LED light. The conversion layer(s)  204  absorbs at least some of the light emitted from the LEDs  104  and re-emits at least some of the absorbed light in a spectrum containing one or more wavelengths that are different from the absorbed light. In various embodiments, the photo-luminescent material(s) contained in the conversion layer(s)  204  is chosen based at least in part on the waveguide material. This is because the waveguide material may cause a larger portion of the blue light from the white LEDs  104 - 2 ,  104 - 3  to be extracted; this may result in a shift of the CCT value of light emitted from the white LEDs  104 - 2 ,  104 - 3  toward a higher CCT value (i.e., cooler white light). In one embodiment, the photo-luminescent material(s) on the conversion layer(s)  204  is chosen such that the wavelength shift thereby can at least partially counteract the shift resulting from the waveguide material as further described below. For example, the same or different photo-luminescent materials (e.g., phosphor QMK58/F-U2) may be applied to shift the CCT value of the light emitted from the cool white LED  104 - 3  toward a green CCT value and/or or to shift the CCT value of the light emitted from the warm white LED  104 - 2  toward a yellow CCT value. 
     In one embodiment, the conversion layer(s)  204  is constructed from a foil that includes a composition of photo-luminescent materials. For example, the foil may be premade using a conventional substrate material (e.g., one or more layers of polymer such as PET) and a binder material (such as silicone); the composition of photo-luminescent materials is then disposed on the substrate surface. Referring to  FIG. 2B , when multiple conversion layers  204  are used, the foils including different compositions of photo-luminescent materials may be placed on top of each other with or without a gap therebetween. In one embodiment, one or more layers made of polymer can be implemented to separate the conversion layers. In addition, a second layer made of the substrate material may be applied to the conversion layer(s)  204  so as to cover the photo-luminescent materials thereon. In some embodiments, the foil in the conversion layer(s)  204  includes one or more quantum dot materials. In addition, the foil may include a quantum dot enhancement film (QDEF) made by 3M Inc. or Nanoco Technology Ltd. to provide a geometry for deploying the quantum dot materials. 
     As described above, the conversion layer(s)  204  may absorb at least some of the light emitted from the LEDs  104  and re-emit (or converts) at least some of the absorbed light in a spectrum containing one or more wavelengths that are different from (typically longer than) the light emitted by the LEDs  104 . The wavelength of the converted light may depend on the composition ratio of the photo-luminescent materials, the characteristics associated with each photo-luminescent material, and the wavelength of the light emitted from LEDs  104 . The LEDs may include a monochrome LED with a narrow band spectrum (e.g., a red LED having a wavelength between approximately 600 nm and approximately 670 nm, a blue LED having a wavelength between approximately 400 nm and approximately 530 nm, and/or an UV LED having a wavelength between approximately 100 nm and approximately 400 nm) and/or a phosphor-converted LED with a wider band spectrum (e.g., the warm white LED  104 - 2  and/or cool white LED  104 - 3 ). The converted and unconverted light may then be mixed in the waveguide material to generate light having a target characteristic (e.g., color and/or CCT value); the target characteristic may be tunable within a range as further described below. 
     In some embodiments, each group of the LEDs depicted in  FIGS. 1A, 1C and 1D  may include one red LED  104 - 1  and two blue LEDs  104 - 2 ,  104 - 3  (instead of one red LED and two white LEDs described above). In addition, referring to  FIG. 2C , the conversion layer(s)  204  may be disposed above the blue LEDs  104 - 2 ,  104 - 3  only, and not the red LED  104 - 1 . The photo-luminescent material(s) may convert at least some of the blue light emitted from the blue LEDs  104 - 2 ,  104 - 3  to light having a longer wavelength. For example, a (Gd, Y) 3 (Al, Ga) 5 O 12  phosphor may convert blue light to yellow light. The converted light (e.g., yellow light) and unconverted blue light may then be mixed to generate white light. Thus, by choosing the photo-luminescent material(s) and/or adjusting the composition thereof, the light emitted from the blue LEDs  104 - 2 ,  104 - 3  may be converted to thereby generate warm white light and cool white light, respectively. In one embodiment, one or more additional conversion layers  204  are utilized to shift the CCT value of the light emitted from the cool white LED  104 - 3  toward a green CCT value and/or or to shift the CCT value of the light emitted from the warm white LED  104 - 2  toward a yellow CCT value as further described below. 
     In some embodiments, the LED array includes blue LEDs only. For example, referring to  FIG. 2D , light emitted from two of the blue LEDs  104 - 2 ,  104 - 3  may be converted to generate warm white light and cool white light as described above. In addition, the conversion layer(s)  204  having suitable photo-luminescent material(s) (e.g., deep-red quantum dots by Nanoco Technology Ltd.) may be disposed above the third blue LEDs  104 - 4  so as to convert the light emitted therefrom to red light having a peak wavelength at approximately 650 nm. Again, the light emitted from the LEDs, including both converted and unconverted light, may be mixed to generate light having a characteristic (e.g., color, CIE chromaticity coordinates and/or CCT value) that is tunable within a range. 
     Referring to  FIG. 2E , in various embodiments, the conversion layer(s)  204  is divided into multiple regions  232 - 242 ; each region is either uncoated or coated with the same or different photo-luminescent materials. For example, regions  232 ,  234  may be uncoated to allow unconverted blue light from the LED to travel through; regions  236 ,  238  may be coated with the first type of photo-luminescent material such that the converted light, after being mixed with the unconverted light, generates cool white light; and regions  240 ,  242  may be coated with the second type of photo-luminescent material such that the converted light, after being mixed with the unconverted light, generates cool white light. Thus, by utilizing different types of photo-luminescent materials having different characteristics at different locations over the LEDs  104 , a target spectral power distribution (SPD) of the light may be achieved. 
     Referring again to  FIG. 2B , the light emitted from an LED  104  may interact with the photo-luminescent material(s) disposed above a neighboring LED, cause a “crosstalk” interaction, and thereby result in additional colors. To reduce the crosstalk interaction, referring to  FIG. 3A , each LED  104  in the strip lighting device  102  may be surrounded by a “cup-shaped” reflector  302 . As shown, each cup-shaped reflector  302  typically has a top aperture  304  and a bottom aperture  306 ; the LED  104  is disposed inside of the bottom aperture  306 . The shapes of the apertures  304 ,  306  may be, for example, circular, elliptical, rectangular, square, etc., and may be the same or different from each other. In one embodiment, the reflectors  302  abut each other such that the bottom portions  308  thereof form a continuous surface. The reflectors  302  may be made of a high reflectivity material, such as MS-2002 silicone from DOWSIL. 
     In some embodiments, the geometry of the cup-shaped reflectors  302  is configured to provide a uniform distribution of the light intensity at a specific distance, D, above the LED  104  where the conversion layer(s)  204  is typically disposed. In one embodiment, the reflector  302  is a parabolic reflector (i.e., a reflecting optic whose reflective surface forms a truncated paraboloid), and the LED  104  is placed at or near the focus of the paraboloid. Thus, a light beam emitted from the LED  104  onto the reflector  302  may be redirected upward for at least partial collimation of the beam. 
     Referring to  FIG. 3B , in various embodiments, an encapsulant material is potted over the LED  104  within a cavity space  310  created by the reflector  302  to at least partially encapsulate the LED  104 . In one embodiment, the height of the encapsulant material above the LED  104  approximately corresponds to the specific distance D described above, thus the light intensity on the top surface  312  of the cavity space  310  may be uniformly distributed without having any visible high intensity spots thereon. The encapsulant material may include, consist of, or consist essentially of a clear material such as silicon. Alternatively, the encapsulant material may form a cover having a convex or domed shape on top of the reflector aperture  304 ; the cavity space  310  can be filled with gas or instead can be under vacuum. In addition, one or more conversion layers  204  including one or more types of photo-luminescent materials (e.g., phosphors, quantum dot materials, etc.) may be coated inside and/or outside the top surface  312  of the encapsulant material to convert the light emitted from the LEDs  104  as described above. In some embodiments, the cavity space  310  is at least partly filled by the encapsulant material that includes a composition of the photo-luminescent material(s) and waveguide material so as to allow the photo-luminescent material(s) to be embedded in the waveguide material. 
     Referring again to  FIG. 2A , in one embodiment, the cavity  202  formed between the circuit board  106  and the conversion layer(s)  204  is filled with a waveguide material (e.g., silicone) such that the waveguide material is in direct contact with the top surface of the circuit board  106  and the conversion layer(s)  204 . In addition, one or more reflectors  210 - 214  may be disposed on the top, bottom and/or side surfaces of the waveguide, respectively, such that the light emitted from the LEDs  104 , including both unconverted and converted light by the conversion layer(s)  204 , can be mixed inside a mixing region  216  of the waveguide; the mixed light then propagates to an output region  218  of the waveguide for outputting the light. In addition, a reflector  219  may be disposed on the top surface of the circuit board  106 . In one embodiment, at least one of the reflectors  210 - 214 ,  219  is made of a high-reflectivity silicone (e.g., CI2001 from DOWSIL). Alternatively, a high-reflectivity foil may be used as one or more of the reflectors  210 - 214 ,  219 . It should be noted that although  FIG. 2A  depicts the LEDs  104  and conversion layer(s)  206  disposed on one side  220  of the waveguide only, they may be disposed on another side  222  with the similar spatial arrangement. In addition, the location of the output region  218  may be anywhere on the waveguide and is not limited to the top surface of the waveguide as depicted in  FIG. 2A . 
     In one implementation, the entire circuit board  106  is encapsulated inside the waveguide; the illumination system  100  may include a heat-conducting path connecting the bottom surface of the circuit board  106  to an outer surface of the waveguide for dissipating heat generating by the LEDs  104 . In one embodiment, the heat-conducting path is formed by using a heat conductive material as a part of the waveguide material and disposing the circuit board  106  to be in directly contact with the waveguide. 
     As discussed above, the LEDs  104  mounted on the circuit board  106  may be controlled individually or in a group manner to generate light having a tunable CCT value within a range. The particular range in which the CCT value can be varied may depend on the configurations of the LEDs, such as the particular combination of the LEDs.  FIG. 4A  depicts exemplary color coordinates  402 ,  404 ,  406  of the warm white LED  104 - 2 , cool white LED  104 - 3 , and red LED  104 - 1 , respectively, in the CIE 1931 color space in accordance with various embodiments. As shown, the color coordinates  402 ,  404 ,  406  form vertices of a triangular region  408 ; thus, the color coordinates of light produced by such a combination of LEDs  104 - 1 ,  104 - 2 ,  104 - 3  can be tuned within the triangular region  408 .  FIG. 4B  depicts an enlarged view of a region of the triangular region  408 . As shown, the CCT value of the light generated by the red LED, warm white LED and cool white LED can be tuned along the Black Body Curve  410  with a deviation of less than 3.0 SDCM (MacAdam&#39;s ellipse). Further details about combining various LEDs to generate white light having a tunable CCT value are provided, for example, in International Application No. WO 2018/157166 (filed on Feb. 27, 2018), the entire content of which is incorporated herein by reference. 
     As described above, the LEDs  104  may be encapsulated in a waveguide material ( FIG. 2A ) and/or an encapsulant material ( FIG. 3B ). As a result, a large portion of the blue light from the LEDs is extracted from the LEDs, which in turn causes shifts of the CCT values associated with the warm white light and cool white light. For example, referring to  FIG. 4C , the color coordinates of the light emitted from the warm white LED  104 - 2  may be shifted from a location  402  (approximately 2700K) to a location  412  (3000K); similarly, the color coordinates of the light emitted from the cool white LED  104 - 3  may be shifted from a location  404  (approximately 6500K) to a location  414  (8000K). The degree of shifting may depend on the material characteristics of the waveguide and/or an encapsulant. It should be noted that because the waveguide material and/or encapsulant material has no (or at least limited) effect on the color coordinates  406  of the red light emitted from the red LED  104 - 1 , there may be no need for applying the photo-luminescent material(s) thereto. 
     In various embodiments, the color coordinate shifts resulting from the waveguide and/or encapsulant are at least partially counteracted by using, for example, one or more photo-luminescent materials (e.g., phosphor QMK58/F-U2) disposed on the conversion layer(s)  204 . In one embodiment, the photo-luminescent material(s) shifts the CCT value of the light emitted from the cool white LED  104 - 3  toward a green CCT value (e.g., from the location  414  to a location  424 ) and/or the (Cx, Cy) value of the light emitted from the warm white LED  104 - 2  toward a yellow (Cx, Cy) value (e.g., from the location  412  to a location  422 ). As a result, the color coordinates of the light generated by mixing the cool white light, warm white light and red light that have color coordinates at locations  424 ,  422 ,  406 , respectively, can be tuned within a new triangular region  428  formed by the new vertices  424 ,  422 ,  406 . In various embodiments, the CCT value of the mixed light can be tuned along the Black Body Curve  410  with a deviation of less than 1.5 SDCM. 
     It should be noted that the green CCT value and yellow CCT value toward which the CCT values of the cool white light and warm white light are shifted do not necessarily correspond to specific CCT values. Rather, referring to  FIG. 4D , the green CCT value and yellow CCT value can be any color coordinates located within the green region  432  and yellow region  434  in the color space. In addition, for purposes hereof, the green region  432  includes all color coordinates in the color space corresponding to wavelengths between approximately 480 nm and approximately 550 nm, and the yellow region  434  includes all color coordinates in the color space corresponding to wavelengths between approximately 550 nm and approximately 590 nm. 
     Referring to  FIG. 4E , in various embodiments, the CCT value of the mixed light is adjusted along the BBC with a deviation of less than 1.5 SDCM so as to match or complement the human circadian rhythm. The adjustment of the CCT value can be achieved by changing the intensity of the light emitted from one or more of the LEDs  104 - 1 ,  104 - 2 ,  104 - 3 . For example, when a target CCT value of the mixed light changes from a location  436  to a location  438  in the color space, the intensity of the cool white LED  104 - 3  may be reduced, while the intensity of the warm white LED  104 - 2  and/or red LED  104 - 1  may be increased. In various embodiments, the intensity contribution of the light from each LED negatively correlates to the distance between the color coordinates of the LED light and the target color coordinates in the color space. For example, assuming the target color coordinates being at the location  438 , because the distance, d 1 , between the color coordinates  422  of the warm white light and the target color coordinates  438  is smaller than the distance, d 2 , between the color coordinates  424  of the cool white light and the target color coordinates  438 , the intensity contribution from the warm white light may be larger than that from the cool white light. Similarly, because the distance d 2  is smaller than the distance, d 3 , between the color coordinates  406  of the red light and the target color coordinates  438 , the intensity contribution from the cool white light may be larger than that from the red light. 
     In some embodiments, the control circuitry  112  adjusts the intensity of the light emitted from one or more of the LEDs  104 - 1 ,  104 - 2 ,  104 - 3  by varying the amplitude and/or duty cycle of the current and/or voltage associated therewith. In addition, the control circuitry  112  may include a look-up table that maps particular target CCT values to a set of intensity ratios for the LEDs within the LED array. Thus, when the control circuitry  112  receives information indicative of a desired CCT value, it may access the look-up table to retrieve the corresponding intensity ratios, and, based thereon, adjust the intensities of the LEDs. 
     Refer now to  FIGS. 5A-5C , which illustrate representative configurations  5001 ,  5002  for combining germicidal UV-A light with light in the visible range to create white light with a desired CCT value. Although the term UV-A commonly refers to the wavelength region 315-400 nm, for purposes of this specification UV-A refers to the broader wavelength region 315-420 nm. In the configuration  5001 , LEDs  104 -U emitting UV-A light are grouped with three other LEDs  104 - 1 ,  104 - 2 ,  104 - 3 . These groups repeat in a linear sequence along a PCB  5101 . In one embodiment, the LEDs  104 - 1  are red and the LEDs  104 - 2  and  104 - 3  are both blue (although they may be different LED types). In the configuration presented in  FIG. 5C , two types of LED emitting UV-A light (e.g., at different wavelengths),  104 -U 1  and  104 -U 2 , are connected in series together with LEDs  104 - 1 —in the top row, LEDs  104 -U 1  are used and in the third row, LEDs  104 -U 2  are used. The alternate (second and fourth) rows consist entirely of a single UV or non-UV LED type. This configuration allows each row to be driven by a single channel and collectively produces white light through the phosphor while also providing UV-A light. 
     The illustrated linear sequence is only one example of groupings, however; in other implementations, the groupings are spread across linear LED sequences as shown in  FIGS. 1C and 1D . 
     Suitable LEDs are as follows: 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                   
               
               
                   
                 104-U1 
                 104-U2 
                 104-3 
                 104-2 
                 104-1 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 LED 
                 LxF3- 
                 LHUV-0405- 
                 SB1515NS 
                 SB1515NS 
                 LXZ1-PD02 
               
               
                   
                 U390100007001 
                 A070 
               
               
                 Peak Wavelength [nm] 
                 395 
                 405 
                 450 
                 450 
                 630 
               
               
                 Radiant Power [mW] 
                 750 
                 750 
                 900 
                 900 
                 350 
               
               
                 Current [mA] 
                 500 
                 500 
                 500 
                 500 
                 500 
               
               
                 Forward Voltage [V] 
                 3.1 
                 3.1 
                 3 
                 3 
                 2.2 
               
               
                 Number of LEDs 
                 8 
                 4 
                 4 
                 8 
                 6 
               
               
                   
               
            
           
         
       
     
     The controller  112  has three output channels A, B, C. Channel A controls the blue LEDs, channel B controls the red LEDs, and channel C controls the UV-A LEDs. Once again, the control circuitry  112  adjusts the intensity of the light emitted from one or more of the LEDs  104 - 1 ,  104 - 2 ,  104 - 3 ,  104 -U by varying the amplitude and/or duty cycle of the current and/or voltage associated therewith. In some embodiments, only the amplitude and/or duty cycle of the visible-light LEDs  104 - 1 ,  104 - 2 ,  104 - 3  is controlled; in other embodiments, the amplitude and/or duty cycle of all LEDs is controlled. 
     In the configuration  5002  shown in  FIG. 5B , the UV-A LEDs are deployed on a single printed circuit board (PCB)  515 , and the LEDs  104 - 1 ,  104 - 2 ,  104 - 3  are deployed on an adjacent PCB  520 . The lighting system may include a sequence of PCBs  515 ,  512 , e.g., alternating or present in different quantities (e.g., two or three PCBs  520  for every PCB  515 ). 
     The conversion layers with photo-luminescent materials may be disposed above some or all of the LEDs, and following conversion, light from all LEDs is mixed in the waveguide as described above. For example, blue light or UV-A light may interact with phosphor material, and some of it is converted to a different color. The converted light and the remaining bluelight are mixed with the red and UV-A light, and extracted out from the waveguide plate to form white light illumination. The red light is used to tune the white light color coordinates to fit the required CCT and to improve CRI values, so it may be necessary to control the amplitude and/or duty cycle only of the red LEDs  104 - 1 . Additional white LED at a specific CCT, may be assembled on the PCB to enable True Tunable White (TTW) functionality—i.e., the ability to tune the CCT along the black-body curve of white light from deep warm (e.g., 1800K) to far cool (e.g., 6500K) with small deviation, i.e., below 1 Macadams ellipse). 
     The UV-A light may interact with the photo-luminescent material and increase the amount of converted light. This will change the CCT of the light. In this case the intensity of the red light may be increased to shift the color coordinates to fit the required CCT. One option is to use a photo-luminescent material having a very low excitation level at the UV-A wavelength (e.g., Yttrium Aluminium Oxide:Cerium Y 3 Al 5 O 12 :Ce), as shown in  FIG. 6 . In this case, the photo-luminescent material will convert less UV-A light to a different color. A second option is to have the phosphor excitation wavelength include the UV-A wavelength as shown in  FIG. 7  (e.g., Yttrium Aluminum Garnet “537 nm”). In this case, the photo-luminescent material will convert more UV-A light to a different color. In implementations where the UV-A LEDs are connected and driven together with the blue or the red LEDs when the system is operated to provide white light, some of the UV-A light will be converted and will change in CCT. In order to maintain the target CCT, the ratio of the red and blue light may be changed. In order to retain an intense UV-A emission, it is desirable to choose a wavelength that does not interact much with the phosphor material. However, placing the UV-A LEDs in the blue channel will reduces the blue light intensity and therefore the converted light. In that case it is preferable to use UV-A LEDs that exhibit greater interaction with the phosphor material in the red channel together with the red LEDs so their light will collectively increase the amount of converted light while increasing the red:blue ratio for maintaining the target CCT. 
     The LED configurations  500  can be organized into a lighting fixture or “luminaire.” In a “normal” mode of operation, the luminaire can provide conventional white light and germicidal UV-A light. For example, the UV-A emission may be ˜7 W together with the required intensity of white light. As shown in  FIG. 8 , each luminaire may, in some embodiments, provide white light over a wide coverage area but UV-A light over a restricted angular range.  FIG. 9  illustrates how this permits a ceiling arrangement  900  of luminaires  910  to illuminate a room-size area  920  with white light but focus UV-A energy on a smaller target area  930 . In particular, the luminaires may operate in a “boost” mode in which the red and UV-A LEDs are active and operated at maximum power, and the blue LEDs are not active; for example, with reference to  FIG. 5A , only output channels B and C are active. As a result, the UV-A intensity (or irradiance in w/m 2 ) in boost mode may be three times that in normal mode, and may exceed the maximum safe intensity (or irradiance) for human exposure. The red light provides a visual indication of danger. Alternatively or in addition, occupancy sensors (such as passive infrared (PIR) sensors, ultrasonic sensors, cameras, etc.) may communicate with the controller  112 , which permits boost-mode operation only when no personnel are detected in the region  930  or even in the room  920 . 
     The control circuitry  112  may include or be connected to one or more modules implemented in hardware, software, or a combination of both. For embodiments in which the functions are provided as one or more software programs, the programs may be written in any of a number of high level languages such as PYTHON, FORTRAN, PASCAL, JAVA, C, C++, C#, BASIC, various scripting languages, and/or HTML. Additionally, the software can be implemented in an assembly language directed to the microprocessor resident on a target computer; for example, the software may be implemented in Intel 80×86 assembly language if it is configured to run on an IBM PC or PC clone. The software may be embodied on an article of manufacture including, but not limited to, a floppy disk, a jump drive, a hard disk, an optical disk, a magnetic tape, a PROM, an EPROM, EEPROM, field-programmable gate array, or CD-ROM. Embodiments using hardware circuitry may be implemented using, for example, one or more FPGA, CPLD or ASIC processors. 
     The terms and expressions employed herein are used as terms and expressions of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof. In addition, having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive.