Patent Publication Number: US-2022211890-A1

Title: Ultraviolet light emitter

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of Patent Cooperation Treaty (PCT) application No. PCT/CA2020/051112 having an international filing date of 13 Aug. 2020, which in turn claims the benefit of priority from, and for the purposes of the United States of America the benefit under 35 USC 119 in relation to, U.S. application No. 62/890,008 filed 21 Aug. 2019. All of the applications referred to in this paragraph are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to ultraviolet (UV) light emitters. Such emitters have applications in, for example, water and air purification. Particular embodiments provide methods and apparatus for emitting desirable UV radiation patterns. 
     BACKGROUND 
     Ultraviolet (UV) light is commonly used for disinfection applications, such as purification or otherwise disinfecting water and/or air. Relatively recently, ultraviolet light emitting diodes (UV-LEDs) have emerged as a desirable source of UV light for such applications. 
     It is known to use a reflector “cup” or “cone” disposed around a light source to help concentrate light emitted from the light source to have directional components in a particular direction. Such a direction is typically aligned with an optical axis of the device employing the light source. In the context of disinfection applications, a reflector cup can increase light efficiency by concentrating light toward a fluid to be treated, for example, or by creating radiation patterns that are more desirable (e.g. more collimated) than the radiation pattern emitted without the reflector cup. 
     UV-LEDs generally have emission patterns that are symmetric about its principal optical axis. State of the art reflector cups are usually designed to be symmetric about an optical axis of the device employing the light source. U.S. Pat. No. 9,789,215 discloses a disinfection system which employs a UV-LED light source and a reflector cup that is symmetric about the principal optical axis of the UV-LED. Aligning a UV-LED&#39;s principal optical axis and a reflector cup&#39;s axis of symmetry may provide a symmetric overall radiation pattern which may be desirable for some applications. 
     One issue with state of the art UV-LED reflector cup designs is that some of the radiation emitted by the UV-LED may not impinge on the reflector cup, if the reflector cup does not extend sufficiently far in the direction of the UV-LED&#39;s principal optical axis. That is some of the radiation within the emission angle ϕ of the UV-LED does not impinge on the reflective surface of the reflector cup and, consequently, such radiation is not directionally controlled by the reflector cup and may be wasted. This problem results in optical inefficiency as some light emitted from the UV-LED may be sub-optimally directed for a particular application. This optical inefficiency results in lesser control of the UV-LED&#39;s rays, as rays that exit the emitter directly, without impinging on the reflector cup, cannot be controlled. In many applications, it is advantageous to control the direction of as many as possible of the rays (i.e. a greater percentage of the light emitted by the emitter). Large reflector cups, which may increase optical efficiency and control over UV rays emitted, require more reflective material which is costly. Large reflector cups are also large and, in many applications, it is desirable to minimize the size of the light emitter. Thus, with prior art UV-LED and reflector cup emitters, there is a trade-off between optical efficiency and control on one hand and cost and size on the other hand. There remains a general desire to address this trade-off. 
     There remains a general desire to provide cost effective UV-LED and reflector cup emitters. There remains a general desire for such UV-LED and reflector cup emitters to be of relatively small size. There remains a general desire for such UV-LED and reflector cup emitters to allow maximum flexibility to designers to maximally control the directionality and distribution of the radiation. 
     The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those skilled in the art upon a reading of the specification and a study of the drawings. 
     SUMMARY 
     The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements. 
     Aspects of the invention include without limitation:
         UV-LED emitting methods and apparatus, which may be used, for example, for delivering UV radiation to a fluid; and   apparatus for reflecting UV-LED radiation to provide desirable UV radiation profiles.       

     One aspect of the invention provides an ultraviolet (UV) radiation emitting assembly comprising: one or more UV-LED(s) having a principal optical axis that is central to the direction of radiation emission from the one or more UV-LED(s); and a reflector located adjacent to the UV-LED(s) and having a three-dimensional shape defined by rotating a smooth and continuous curve having two end points about a principal reflector axis over a reflector angle A, where the reflector angle A is in a range of 120°-300°, the principal reflector axis intersecting the curve at one of the two end points and at no other points on the curve. The principal optical axis of the UV-LED(s) is directed toward the reflector. 
     The curve may be a portion of a parabola. The curve may be a portion of an ellipse. The curve may be a portion of a circular arc. The curve may be a straight line. The curve may comprise a first portion that is a portion of a parabola and a second portion that is a portion of an ellipse. 
     The reflector may comprise material suitable for predominantly specular reflection of UV light (e.g. light having wavelengths in a range of 250-300 nm). 
     The principal optical axis of each UV-LED may form an angle α with the principal reflector axis, the angle α may be in a range of 45°-135°. The principal optical axis of each UV-LED may form an angle α with the principal reflector axis, the angle α may be in a range of 85°-95°. 
     The one or more UV-LED(s) may comprise a plurality of UV-LEDs arranged symmetrically about a focal point of the reflector. The plurality of UV-LEDs may be located on the principal reflector axis. 
     The one or more UV-LED(s) may comprise one UV-LED located on the principal reflector axis at a focal point of the reflector. 
     Each UV-LED may be located within a circle centered at the principal reflector axis and may have a radius of ⅕ of a distance between the reflector and the principal reflector axis measured at an axial location of the UV-LED. Each UV-LED may be located within a distance of 5 times a dimension of the UV-LED of the focal point of the reflector. 
     The three-dimensional shape may be shaped to capture radiation emitted from the one or more UV-LED(s) from at least 67% of an effective emission angle ϕ over which the UV-LED(s) emits radiation. The three-dimensional shape may be shaped to capture radiation emitted from the one or more UV-LED(s) over a emission angle ϕ greater than ϕ=50°. 
     The UV radiation emitting assembly may comprise an optical sensor located adjacent to the reflector for measuring radiation emitted by the radiation emitting assembly. 
     The reflector may be fabricated at least partially by a thermally conductive material and is shaped for dissipating heat generated by the UV-LED(s). 
     The UV radiation emitting assembly may be used for a surface disinfection application. The UV radiation emitting assembly may be used for a flowing water disinfection application. The reflector may be shaped to collimate radiation emitted from the UV-LED(s) such that the collimated direction is generally parallel (within a solid angle of 15°) with an average flow direction of the water in the flowing water disinfection application. The UV radiation emitting assembly may be used for a still water disinfection application. 
     Another aspect of the invention provides an ultraviolet (UV) radiation emitting assembly comprising: one or more UV-LED(s) having a principal optical axis that is central to the direction of radiation emission from the one or more UV-LED(s); and a reflector located adjacent to the UV-LED(s) and having a three-dimensional shape defined by rotating a smooth and continuous curve having two end points about a principal reflector axis over a reflector angle θ, where the reflector angle θ is less than 360°, the principal reflector axis intersecting the curve at one of the two end points and at no other points on the curve. The principal optical axis of the UV-LED(s) is directed toward the reflector. The three-dimensional shape is shaped to capture radiation emitted from the one or more UV-LED(s) from at least 67% of an effective emission angle ϕ over which the UV-LED(s) emits radiation. 
     The curve may be a portion of a parabola. The curve may be a portion of an ellipse. The curve may be a portion of a circular arc. The curve may be a straight line. The curve may comprise a first portion that is a portion of a parabola and a second portion that is a portion of an ellipse. 
     The reflector may comprise material suitable for predominantly specular reflection of UV light (e.g. light having wavelengths in a range of 250-300 nm). 
     The principal optical axis of each UV-LED may form an angle α with the principal reflector axis, the angle α may be in a range of 45°-135°. The principal optical axis of each UV-LED may form an angle α with the principal reflector axis, the angle α may be in a range of 85°-95°. 
     The one or more UV-LED(s) may comprise a plurality of UV-LEDs arranged symmetrically about a focal point of the reflector. The plurality of UV-LEDs may be located on the principal reflector axis. 
     The one or more UV-LED(s) may comprise one UV-LED located on the principal reflector axis at a focal point of the reflector. 
     Each UV-LED may be located within a circle centered at the principal reflector axis and may have a radius of ⅕ of a distance between the reflector and the principal reflector axis measured at an axial location of the UV-LED. Each UV-LED may be located within a distance of 5 times a dimension of the UV-LED of the focal point of the reflector. 
     The reflector angle A may be in a range of 120°-300°. 
     The three-dimensional shape may be shaped to capture radiation emitted from the one or more UV-LED(s) from at least 67% of an effective emission angle ϕ over which the UV-LED(s) emits radiation. The three-dimensional shape may be shaped to capture radiation emitted from the one or more UV-LED(s) over a emission angle ϕ greater than ϕ=50°. 
     The UV radiation emitting assembly may comprise an optical sensor located adjacent to the reflector for measuring radiation emitted by the radiation emitting assembly. 
     The reflector may be fabricated at least partially by a thermally conductive material and is shaped for dissipating heat generated by the UV-LED(s). 
     The UV radiation emitting assembly may be used for a surface disinfection application. The UV radiation emitting assembly may be used for a flowing water disinfection application. The reflector may be shaped to collimate radiation emitted from the UV-LED(s) such that the collimated direction is generally parallel (within a solid angle of 15°) with an average flow direction of the water in the flowing water disinfection application. The UV radiation emitting assembly may be used for a still water disinfection application. 
     Another aspect of the invention provides an ultraviolet (UV) radiation emitting assembly comprising: one or more UV-LED(s) having a principal optical axis that is central to the direction of radiation emission from the one or more UV-LED(s); and a reflector located adjacent to the UV-LED(s), the reflector having a three-dimensional shape and a principal reflector axis. The three-dimensional shape spans an angular range A in a range of 120°-300° about the principal reflector axis. For each axial cross-section plane that includes the principal reflector axis and intersects the three-dimensional shape, a surface of the three-dimensional shape is defined by a smooth and continuous cross-section curve having a first endpoint and a second endpoint, the first end point intersected by the principal reflector axis. For at least two such axial cross-section planes, the corresponding smooth and continuous cross-section curves are different from one another. The defined three-dimensional shape varies smoothly between the cross-section curves. The principal optical axis of the UV-LED(s) is directed towards the reflector. 
     The reflector may comprise material suitable for predominantly specular reflection of UV light (e.g. light having wavelengths in a range of 250-300 nm). 
     The principal optical axis of each UV-LED may form an angle α with the principal reflector axis, the angle α may be in a range of 45°-135°. The principal optical axis of each UV-LED may form an angle α with the principal reflector axis, the angle α may be in a range of 85°-95°. 
     The one or more UV-LED(s) may comprise a plurality of UV-LEDs arranged symmetrically about a focal point of the reflector. The plurality of UV-LEDs may be located on the principal reflector axis. 
     The one or more UV-LED(s) may comprise one UV-LED located on the principal reflector axis at a focal point of the reflector. 
     Each UV-LED may be located within a circle centered at the principal reflector axis and may have a radius of ⅕ of a distance between the reflector and the principal reflector axis measured at an axial location of the UV-LED. Each UV-LED may be located within a distance of 5 times a dimension of the UV-LED of the focal point of the reflector. 
     The three-dimensional shape may be shaped to capture radiation emitted from the one or more UV-LED(s) from at least 67% of an effective emission angle ϕ over which the UV-LED(s) emits radiation. The three-dimensional shape may be shaped to capture radiation emitted from the one or more UV-LED(s) over a emission angle ϕ greater than ϕ=50°. 
     The UV radiation emitting assembly may comprise an optical sensor located adjacent to the reflector for measuring radiation emitted by the radiation emitting assembly. 
     The reflector may be fabricated at least partially by a thermally conductive material and is shaped for dissipating heat generated by the UV-LED(s). 
     The UV radiation emitting assembly may be used for a surface disinfection application. The UV radiation emitting assembly may be used for a flowing water disinfection application. The reflector may be shaped to collimate radiation emitted from the UV-LED(s) such that the collimated direction is generally parallel (within a solid angle of 15°) with an average flow direction of the water in the flowing water disinfection application. The UV radiation emitting assembly may be used for a still water disinfection application. 
     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein be considered illustrative rather than restrictive. 
         FIG. 1  is a schematic perspective view of a light emitting assembly comprising a UV-LED and a reflector according to an example embodiment of the invention. 
         FIG. 1A  shows a curve rotatable about an axis to define the shape of a reflector according to an example embodiment of the invention. 
         FIG. 1B  is a schematic diagram depicting some characteristics of an example radiation pattern emitted by a UV-LED. 
         FIGS. 2A and 2B  are schematic axial cross-sectional diagrams of example light emitting assemblies comprising a UV-LED and a reflector cone. 
         FIG. 3  is a perspective view of a freeform reflector according to an example embodiment of the invention. 
         FIG. 3A  is a transverse elevation view of the reflector shown in  FIG. 3 .  FIGS. 3B and 3C  are different axial cross sectional views of the reflector shown in  FIG. 3 . 
         FIG. 4  is a schematic perspective view of a specific example embodiment of the  FIG. 3  freeform reflector.  FIG. 4A  is a schematic transverse cross section of the reflector shown in  FIG. 4 . 
         FIG. 5A  is a schematic diagram depicting one way of combining multiple light emitting assemblies according to an example embodiment of the invention. 
         FIG. 6  is a schematic perspective view of a light emitting assembly comprising a UV sensor according to an example embodiment of the invention. 
     
    
    
     DESCRIPTION 
     Throughout the following description specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense. 
     As used in this disclosure and in the accompanying claims, unless the context dictates otherwise, the term light should include electromagnetic radiation that may be both inside and outside of the human-visible spectrum. As used in this disclosure and in the accompanying claims, unless the context dictates otherwise, the terms ultraviolet light, UV light, ultraviolet radiation and UV radiation should be understood to include electromagnetic radiation that comprises at least some light having a wavelength shorter than that of the visible spectrum but which may also comprise light that is in the human-visible spectrum. In some exemplary and non-limiting embodiments, the UV radiation used has wavelengths in a range of 250 nm-300 nm. 
       FIG. 1  is a perspective view of a light emitting assembly  10  comprising one or more UV-LEDs  20  (a single UV-LED  20  in the case of the illustrated embodiment) coupled to a UV reflector  100  according to an example embodiment of the invention. Reflector  100  comprises a dominantly specular reflective surface  110  made of materials suitable for reflecting UV light  21  (e.g. aluminum and/or the like) emitted by UV-LED  20 , in a specular fashion. UV-LED  20  is located adjacent to reflector  100  and is oriented such that its principal optical axis  22  is directed towards reflective surface  110  of reflector  100  instead of towards disinfection target  12  (e.g. fluid). Hence, UV light  21  emitted by UV-LED  20  along principal optical axis  22  impinges on reflective surface  110 . 
       FIG. 1A  is a schematic illustration showing characteristics of possible example shapes of reflective surface  110  of reflector  100  of the  FIG. 1  light emitter assembly  10 . For brevity, this disclosure and/or the accompanying claims may refer to the shape of a reflector. Unless the context dictates otherwise, the shape of a reflector should be understood to refer to the shape of the reflective surface of the reflector. Referring simultaneously to  FIGS. 1 and 1A , reflector  100  may comprise a three-dimensional shape defined by rotating a smooth and continuous curve  50  having end points  51  and  52  about a principal reflector axis  101  that intersects one of the end points ( 51  in the case of the illustrated embodiment) over a reflector angle A measured about principal reflector axis  101 . In some embodiments, reflector angle A may be in a range between 120°-360°. In some embodiments, this reflector angle A is greater than 120°, but less than 360°. In some embodiments, this reflector angle A may be in a range between 120°-300°. In some embodiments, this reflector angle A may be in a range between 120°-270°. In some embodiments, this reflector angle A may be in a range between 120°-200°. In the specific case of the  FIG. 1  illustrated embodiment, principal reflector axis  101  is co-linear with the rotational axis of symmetry of a notional quadratic surface  100 ′, where the notional quadratic surface  100 ′ includes the reflective surface  110  of reflector  100  and spans a full 360° angular range about principal reflector axis  101 . In the specific case of the  FIG. 1  illustrated embodiment, principal reflector axis  101  is co-linear with the rotational axis of symmetry of a notional paraboloid surface  100 ″, where the notional paraboloid surface  100 ″ includes the reflective surface  110  of reflector  100  and spans a full 360° angular range about principal reflector axis  101 . Neither of these properties of the shape of reflector  100  (or its reflective surface  110 ) are necessary. In some embodiments, the shape of reflector  100  may comprise a three-dimensional shape defined by rotating an arbitrary smooth and continuous curve  50  having end points  51  and  52  about a principal reflector axis  101  that intersects one of the end points ( 51  in the case of the illustrated embodiment) over a reflector angle A measured about principal reflector axis. 
     In some embodiments, principal reflector axis  101  intersects curve  50  at only one of end points  51  and  52  (and no other points). In some embodiments, principal reflector axis  101  is aligned to point toward the direction of a disinfection target  12  (e.g. fluid). 
     In the  FIG. 1  example embodiment, reflector  100  has the shape of a “half-paraboloid” formed by sweeping a parabolic curve  50  about principal reflector axis  101  over a 180° reflector angle θ. In other embodiments, reflector  100  may take on other shapes (e.g. a “quarter-ellipsoid”, a “half-cone”, etc.) depending on the shape of curve  50  and/or the reflector angle θ. Curve  50  may be a parabola, a fraction (e.g. a quarter) of an ellipse, an arc, a line, or any other suitable smooth and continuous function. 
     Principal optical axis  22  of UV-LED  20  and principal reflector axis  101  intersect to form a polar angle α. In the illustrated embodiment of  FIG. 1 , principal optical axis  22  is orthogonal to principal reflector axis  101  (i.e. α=90°). This is not necessary. In some embodiments, polar angle α between principal optical axis  22  and principal reflector axis  101  may span an angular range between 45° and 135°. 
     UV-LED  20  may be optionally located on principal reflector axis  101  or close to principal reflector axis  101  (e.g. within a circle of ⅕ the reflector&#39;s spacing from principal reflector axis  101  measured at the axial location of UV-LED  20 ). By positioning UV-LED  20  on or close to principal reflector axis  101 , assembly  10  can advantageously emit symmetric radiation patterns. In some embodiments, UV-LED  20  may be located on (or close to—e.g. within a circle of ⅕ the reflector&#39;s spacing from principal reflector axis  101  measured at the axial location of UV-LED  20  from) the focal point of notional quadratic surface  100 ′ or notional paraboloid surface  100 ″. Neither of these characteristics of the location of UV-LED  20  is necessary. 
       FIG. 1B  is a schematic diagram depicting some characteristics of an example radiation pattern emitted by an example UV-LED  20 . UV-LED  20  emits a central ray  21 A from a center  23  of UV-LED  20  along principal optical axis  22 . Central ray  21 A may be oriented to be generally normal (e.g. ±10°) to the surface of UV-LED  20 . UV-LED  20  emits UV light  21  in other directions. The angle between central ray  21 A (or principal optical axis  22 ) and rays of UV light  21  emitted in other directions defines an emission angle ϕ of UV-LED  20 . At locations equidistant from center  23  of UV-LED  20 , the intensity of UV light  21  may be generally highest along principal optical axis  22  (i.e. ϕ=0°) and progressively lower at higher emission angles. In some embodiments, the intensity of UV light  21  emitted by UV-LED  20  at emission angles greater than ϕ=75° may be negligible or may be considered to be negligible for the purpose of disinfection applications. The emission angle ϕ greater than which the intensity of UV light  21  emitted by UV-LED  20  is negligible (e.g. less than 2% of the total radiation power) may be referred to as the effective emission angle ϕ of UV-LED  20 . 
       FIGS. 2A and 2B  are schematic axial cross-sectional diagrams of UV-LED  20  emitting UV light  21  into a UV reflector  100  according to example embodiments of the invention. In this disclosure and the accompanying claims, unless the context dictates otherwise, an axial cross-section may be considered to be a cross-section in a plane that includes the principal reflector axis  101  of a UV reflector  100 .  FIGS. 2A and 2B  schematically depict axial cross-sections in planes that include a line segment corresponding to the reflective surface  110  of reflector  100  and principal reflector axis  101 . In the illustrated embodiments of  FIGS. 2A and 2B , the axial cross-sectional line segment of reflective surface  110  of reflector  100  has a parabolic shape. In some embodiments, the axial cross-sectional line segment of reflective surface  110  of reflector  100  may have other smooth and continuous shapes. In the example embodiments of  FIGS. 2A and 2B , UV-LED  20  is located on principal reflector axis  101  at a focal point of the shape of the axial cross-sectional line segment of reflective surface  110  of reflector  100  (e.g. at the focal point of a partial parabolic segment). In the example embodiments of  FIGS. 2A and 2B , principal optical axis  22  of UV-LED  20  is orthogonal to principal reflector axis  101 . 
     In the  FIG. 2A  example embodiment, the length of reflector  100 A along its principal reflector axis  101  is relatively short (i.e. 10 mm). As a result, only UV light  21  emitted by UV-LED  20  at emission angles smaller than ϕ=53.1° impinges on reflector  100 A. 
     In the  FIG. 2B  example embodiment, the length of reflector  100 B along its principal reflector axis  101  is two and a half times longer than that of reflector  100 A (i.e. 25 mm). As a result, UV light  21  emitted by UV-LED  20  at emission angles up to ϕ=72.3° impinges on reflector  100 B. 
     In some embodiments, the length of reflector  100  is selected to balance the trade-off between capturing light emitted by UV-LED  20  at higher emission angles (ϕ) and minimizing size and/or costs associated with providing a larger reflector  100 . It will be appreciated that the emission angle of a UV-LED  20  is a property of the LED itself and, consequently, for a given UV-LED  20 , capturing light emitted at higher emission angles (ϕ) may be correlated with allowing optimum directional control of the radiation (e.g. a percentage of light emitted by UV-LED  20  that is usable for a given purpose, such as a disinfection application). 
     In some embodiments, the shape of reflector  100  (e.g. the length of reflector  100  along its principal reflector axis  101  and/or the reflector angle A measured about principal reflector axis  101 ) is designed to capture radiation emitted from at least 67% of the effective UV-LED emission angle ϕ over which UV-LED  20  emits radiation—i.e. 67% or more of the radiation from UV-LED  20  over its effective emission angle ϕ impinges on reflector  100 . In some embodiments, reflector  100  is shaped so that 75% or more of the radiation from UV-LED  20  over its effective emission angle ϕ impinges on reflector  100 . In some embodiments, reflector  100  is shaped so that 85% or more of the radiation from UV-LED  20  over its effective emission angle ϕ impinges on reflector  100 . In some embodiments, reflector  100  is shaped so that 90% or more of the radiation from UV-LED  20  over its effective emission angle ϕ impinges on reflector  100 . 
     In some embodiments, the shape of reflector  100  (e.g. the length of reflector  100  along its principal reflector axis  101  and/or the reflector angle θ measured about principal reflector axis  101 ) is designed to capture radiation emitted from a emission angle ϕ greater than ϕ=50°. That is, reflector  100  is shaped such that radiation emitted at an emission angle less than ϕ=50° impinges on reflector  100 . In some embodiments, reflector  100  is shaped such that radiation emitted at an emission angle less than ϕ=60° impinges on reflector  100 . In some embodiments, reflector  100  is shaped such that radiation emitted at an emission angle less than ϕ=70° impinges on reflector  100 . In some embodiments, reflector  100  is shaped such that radiation emitted at an emission angle less than ϕ=75° impinges on reflector  100 . 
     In some embodiments, the polar angle α (see  FIG. 1 ) between principal optical axis  22  of UV-LED  20  and principal reflector axis  101  is selected to balance the above-mentioned trade-off and/or to provide a more desirable UV radiation profile. For example, UV-LED  20  may be oriented towards a base  111  of reflective surface  110  (see  FIGS. 2A, 2B ) which corresponds to α&gt;90° or away from base  111  of reflective surface  110  which corresponds to α&lt;90°. Titling UV-LED  20  towards base  111  (α&gt;90°) may allow reflector  100  to capture more UV light  21  at higher emission angles (ϕ) without increasing the length of reflector  100 . Titling UV-LED  20  away from base  111  (α&lt;90°) may allow more UV light  21  to impinge directly on disinfection target  12  (without reflecting from reflector  100 ). 
       FIG. 3  is a perspective view of a freeform UV reflector  200  according to another example embodiment of the invention. Reflector  200  is similar in many respects to reflector  100  and features of reflector  200  that are similar to reflector  100  may be labelled using reference numbers that are similar to those used for reflector  100 , except that the reference numerals used for reflector  200  use a first digit  2 , whereas the reference numerals used for reflector  100  use a first digit  1 . Similarly to reflector  100 , reflector  200  comprises a reflective surface  210  made of materials suitable for reflecting UV light  21  emitted by UV-LED  20 . UV-LED  20  (not shown) may be located adjacent to reflector  200  and suitably oriented to emit UV light  21  in directions that impinge on reflective surface  210 . In some embodiments, the principal optical axis  22  of such a UV-LED  20  may be orthogonal to the principal reflector optical axis  201  (i.e. α=90°), although this is not necessary. 
     Reflector  200  has a smooth and continuous three-dimensional shape defined by smoothly varying surfaces between a plurality of different smooth and continuous curves  50 A,  50 B,  50 C,  50 D (collectively, curves  50 ) having a common first end point  51  and respective second ends points  52 A,  52 B,  52 C,  52 D (collectively, end points  52 ). Curves  50  are angularly spaced apart about a principal reflector axis  201  of reflector  200  and the reflective surface  210  of reflector  200  is shaped such that its three-dimensional shape is smooth and continuous, includes curves  50  and spans an angle A about principal reflector axis  201  of reflector  200  (see  FIG. 3A ). In some embodiments, the angle A spanned by reflective surface  210  of reflector  200  is in a range between 120°-360°. In some embodiments, this reflector angle A is greater than 120°, but less than 360°. In some embodiments, this reflector angle A may be in a range between 120°-300°. In some embodiments, this reflector angle A may be in a range between 120°-270°. In some embodiments, this reflector angle A may be in a range between 120°-200°. In some embodiments, principal reflector axis  201  may be defined as an axis intersecting the common first end point  51  of all curves  50 . In some embodiments, curves  50  may be symmetric with respect to a plane that includes principal reflector axis, although this is not necessary 
       FIG. 3A  is a schematic transverse elevation view of reflector  200 , where the transverse view shown in  FIG. 3A  is from a perspective where a normal to the transverse plane is aligned with principal reflector axis  201 . In the particular case of the illustrated  FIG. 3A  embodiment, the curvature of reflector  200  between angularly adjacent second end points  52  of angularly adjacent curves  50  form arcs in the  FIG. 3A  view, but this is not necessary. In some embodiments, the curvature of reflector  200  between angularly adjacent second end points  52  of angularly adjacent curves  50  form other smooth and continuous shapes as they span the angle A about principal reflector axis  201 . 
       FIGS. 3B and 3C  are axial cross sectional planar views of reflector  200 .  FIGS. 3B and 3C  respectively depict axial cross sections of reflector  200  at reflector angles θ B  and θ C  which respectively correspond to second end points  52 A,  52 B. Each axial cross section plane includes principal reflector axis  201  and intersects reflector  200  at various points along its reflective surface. These points form curves  50  having first and second end points  51  and  52  in the  FIGS. 3B and 3C  views. Curves  50  are smooth and continuous between end points  51  and  52 . In some embodiments, curves  50  intersect principal reflector axis  201  only at their common first end points  51  (and no other points). 
     In the  FIG. 3  example embodiment, an axial cross section of reflector  200  at a first reflector angle θ B =90° comprises a first curve  50 A having first and second end points  51 ,  52 A (see  FIG. 3B ) while an axial cross section of reflector  200  at a second reflector angle θ C =50° comprises a second curve  50 B having first and second end points  51 ,  52 B (see  FIG. 3C ). In some embodiments, reflector  200  is shaped so that axial cross sections at different reflector angles A provide different curves  50 . In some embodiments, curves  50  may be unique as between different reflector angles θ. In some embodiments, curves  50  may be mirror symmetric about a plane defined by principal reflector axis  201  and a vector directed towards a specific reflector angle θ′. 
     In some embodiments, reflector  200  is symmetric about a plane intersecting principal reflector axis  201  and reflector  200  at a reflector angle θ′. Reflectors  200  with such designs may advantageously provide radiation patterns that are more symmetric than reflectors that do not exhibit such symmetry. 
       FIG. 4  is a schematic perspective view of a specific example embodiment  200 A of the  FIG. 3  freeform reflector  200 . Freeform reflector  200 A is a specific embodiment of the  FIG. 3  freeform reflector  200 , where each of curves  50  has a parabolic shape to provide a corresponding parabolic curve  50 E having end points  51 ,  52 E. Parabolic curves  50 E may have different foci at different reflector angles θ. Parabolic curves  50 E may optionally share a common vertex at their respective first end points  51 . 
     In the  FIG. 4  example embodiment, reflector  200 A spans an angular range A about principal reflector axis  201  that is in a range between 120°-360°. In some embodiments, this reflector angle A is greater than 120°, but less than 360°. In some embodiments, this reflector angle A may be in a range between 120°-300°. In some embodiments, this reflector angle A may be in a range between 120° 270°. In some embodiments, this reflector angle A may be in a range between 120°-200°. Reflector  200 A is symmetric about a plane of symmetry  202  containing principal reflector axis  201  and curve  50 E at reflector angle θ=θ′=90°. Reflector  200 A is shaped so that the axial distance between principal reflector axis  201  and reflector  200 A is greatest at reflector angle θ=θ′=90°, and progressively smaller at increasingly higher and decreasingly lower reflector angles. 
       FIG. 4A  is a schematic planar view of a transverse cross section of reflector  200 A coupled to UV-LED  20 , where a plane of the transverse cross-section has a normal that is parallel with principal reflector axis  201 . UV-LED  20  is located adjacent to reflector  200 A on (or close to, as defined for other embodiments herein) principal reflector axis  201 . For any given cross-section, L 1  represents a distance between principal reflector axis  201  and reflective surface  210  of reflector  200 A where the distance L 1  is oriented in a direction that is parallel with principal optical axis  22  of UV-LED  20 . 
     For a given transverse cross-section, the distance L 1  may represent a maximum distance between principal reflector axis  201  and reflective surface  210  of reflector  200 A in some embodiments. L 2 , which may be oriented in a direction that is orthogonal to both principal optical axis  22  and principal reflector axis  201 , may represent a minimum distance between principal reflector axis  201  and reflective surface  210  of reflector  200 A in some embodiments. L 1  and L 2  respectively measure 8 mm and 6 mm in the example embodiment shown in  FIG. 4A . 
     UV-LED  20  may be oriented so that its principal optical axis  22  lies in plane of symmetry  202 . Principal optical axis  22  (and/or plane of symmetry  202 ) and the y-axis shown in the  FIG. 4A  view (which is oriented along the direction of L 2 ) intersect to form an azimuthal angle β. Azimuthal angle β may span an angular range between 60°-180°. In some embodiments, this azimuthal angle β may span a range between 60°-150°. In some embodiments, this azimuthal angle β may span a range between 60°-135°. In some embodiments, this azimuthal angle β may span a range between 60°-100°, in some embodiments. Principal optical axis  22  (and/or plane of symmetry  2020 ) is perpendicular to the y-axis (i.e. β=90°) in the example embodiment shown in  FIG. 4A . 
     The example arrangement shown in  FIGS. 4 and 4A  may assist in normalizing the flux across the full output area bounded by endpoints  52 E of reflector  200 A. A more uniform optical flux advantageously allows assembly  10  to deliver more uniform doses of UV radiation to disinfection target  12 . 
     In some embodiments, as shown for example in  FIGS. 4 and 4A , the reflector comprises a relatively narrow opening  14  in the Y-Z plane for high angle rays (i.e. rays oriented an angle greater than 30° from principal optical axis  22 ) and a relatively wide opening  14  in the Y-Z plane for central rays (i.e. rays within an angle of 30° from principal optical axis  22 ). However, this is not mandatory. 
     Reflector  200  may be suitably designed in other embodiments to provide other UV radiation profiles across the output area bounded by endpoints  52  of reflector  200 . Reflector  200  may be designed based on factors including, but not limited to: the orientation of UV-LED  20  (i.e. polar angle α, azimuthal angle β), the location of UV-LED  20  relative to principal reflector axis  201 , and the radiation profile of UV-LED  20  across various emission angles  4 ). 
     In some embodiments, reflector  200  is designed to help assembly  10  provide more concentrated collimated radiation patterns (e.g. where UV-LED  20  is located at the focal point of a paraboloid-shaped reflector). 
     In some embodiments, two or more light emitting assemblies  10  may be combined to provide suitable UV radiation patterns. 
     Combining Multiple Light Emitting Assemblies 
       FIG. 5A  is a schematic diagram depicting example ways of combining multiple light emitting assemblies  10  according to a particular example embodiment. Assemblies  10 A and  10 B may be positioned “back-to-back” to cover angular ranges exceeding Θ=180°. For example, a first reflector  200 A of a first assembly  10 A may span an angular range Θ A  of up to 180° about its principal reflector axis  201 A, while a second reflector  200 B of a second assembly  10 B may span an angular range Θ B  which may be up to 180° about its principal reflector axis  201 B. 
     In the  FIG. 5A  example embodiment, each light assembly  10  comprises a UV-LED  20  coupled to a corresponding reflector  200 A,  200 B. Reflectors  200 A,  200 B may be identical and oriented so that they are mirror symmetric with each other about an x-y plane located between their respective principal reflector axes  201 . In some embodiments, assemblies  10 A and  10 B may comprise reflectors  200 A,  200 B that have different three-dimensional shapes. 
     In the  FIG. 5A  example embodiment, UV-LED  20 A of assembly  10 A and UV-LED  20 B of assembly  10 B are oriented so that their principal optical axes  22 A and  22 B are aligned with each other (e.g. are co-linear) but face opposite directions. This may advantageously provide a radiation profile that is mirror symmetric about an x-y plane located between principal reflector axes  201 . 
     Other possible design variations for combining assemblies  10  include, but are not limited to: combining multiple (i.e. more than two) assemblies  10 , orienting UV-LEDs  20  at different polar angle α and/or azimuthal angles  13  for different assemblies  10 , orientating reflectors at different reflector polar and/or azimuthal angles for different assemblies  10 , and combining assemblies  10  having reflectors that span different ranges of reflector angles. 
     Supplementary UV Sensor 
       FIG. 6  is a schematic perspective view of a light emitting assembly  10  comprising a UV sensor  24  according to an example embodiment. Like UV-LED  20 , UV sensor  24  is located adjacent to reflector  200 . UV sensor  24  detects UV light  21  emitted by UV-LED  20  to actively monitor the condition of UV-LED  20 . UV sensor  24  may detect stray diffuse reflections and observe back reflections in some embodiments. 
     UV sensor  24  may be located nearer to opening  14  (in the Y-Z plane) relative to UV-LED  20  in some embodiments, although this is not necessary. Locating UV sensor  24  near opening  14  advantageously allows UV sensor  24  to capture sufficient diffuse reflection from UV-LED  20  to measure the power of assembly  10  more accurately. Alternate embodiments can locate the UV sensor  24  in a more recessed position relative to UV-LED  20 . UV sensor  24  may comprise or may be connected to a suitable control circuit or logic circuit, which may optionally transmit a warning signal to a user and/or external computing device if it detects insufficient power delivered by UV-LED  20 . 
     In some embodiments, UV sensor  24  is fabricated on the same printed circuit board assembly (PCBA) as UV-LED  20 . This can advantageously simplify manufacturing and minimize costs. 
     Some embodiments provide supplementary systems and apparatus for managing the thermal dissipation of UV-LED  20 . For example, UV-LED  20  may be fabricated and/or mounted on a thermally conductive PCBA substrate in thermo-mechanical contact with a heat sink. Reflectors  100 ,  200  may act as heat sink in some embodiments. For these embodiments, reflectors  100 ,  200  are constructed from materials that are both thermally conductive and optically reflective. Suitable materials include aluminum and/or other predominantly specularly reflective materials. 
     Aspects of the present invention includes a variety of possible supplementary designs to light emitting assembly  10  and/or other aspects of light emitting assembly  10 . These variations may be applied to all of the embodiments described above, as suited, and include, without limitation the following:
         reflector  100  may be interchanged with reflector  200 ; and   UV sensor  24  can be incorporated into any suitable assembly  10 .       

     The emitters described herein advantageously provide design flexibility with respect to controlling the directionality of the majority of emitted rays. Such flexibility is advantageous in a number of non-limiting example applications. On such example application relates to surface disinfection applications, where there is a desire to illuminate a specific surface region. There may be a similar desire to avoid illuminating one or more other regions, such as for safety or material incompatibility reasons, for example. Controlling the direction of emitted rays allows the designer flexibility to achieve selective surface illumination applications. 
     A second example application for the emitters described herein relates to flowing water disinfection generally, where the emitter is part of a disinfection apparatus and is used in conjunction with a vessel or conduit through which water flows, typically with an optical window separating the optical emitter from the vessel/conduit through which water flows. 
     Flexibility to control the directionality of the rays from the emitter allows the designer to selectively localize the distribution of irradiance into the flowing water to optimize the outcome disinfection provided by the disinfection apparatus. A third non-limiting application is a more specific embodiment of the second example. In some flowing water disinfection apparatus, there may be a desire that the path of the light rays is near parallel to the average flow direction of the flowing water. Having flexible control of the directionality of the light rays may permit the achievement this desire. By way of non-limiting example, reflective surfaces with paraboloid like shapes allow near collimation of the majority of light rays which in turn allows alignment with the average flow direction of the flowing water. 
     Another non-limiting example application which may take advantage of the flexibility of controlling the directionality of light rays using the emitters described herein relates to tank-top applications for standing water vessel. In such example applications, the flexibility to control of the directionality of the rays from the emitters allows the rays to be distributed preferentially into corners or otherwise dark areas of the standing water vessel to maximize disinfection efficiency. 
     Specific examples of systems, methods and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions, and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments. 
     Various features are described herein as being present in “some embodiments”. Such features are not mandatory and may not be present in all embodiments. Embodiments of the invention may include zero, any one or any combination of two or more of such features. This is limited only to the extent that certain ones of such features are incompatible with other ones of such features in the sense that it would be impossible for a person of ordinary skill in the art to construct a practical embodiment that combines such incompatible features. Consequently, the description that “some embodiments” possess feature A and “some embodiments” possess feature B should be interpreted as an express indication that the inventors also contemplate embodiments which combine features A and B (unless the description states otherwise or features A and B are fundamentally incompatible). 
     While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are consistent with the broadest interpretation of the specification as a whole.