Patent Publication Number: US-8967821-B2

Title: Lighting device with low glare and high light level uniformity

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Phase of International Application No. PCT/US 10/49564 having an international filing date of Sep. 21, 2010, published in English on Mar. 31, 2011, which claims the benefit of U.S. Patent Application No. 61/245,688, filed Sep. 25, 2009, the entirety of which is incorporated herein by reference as if set forth in its entirety. 
    
    
     FIELD OF THE INVENTIVE SUBJECT MATTER 
     The present inventive subject matter relates to a lighting device that provides low glare and good uniformity of light level. In some embodiments, the present inventive subject matter relates to a lighting device that includes one or more solid state light emitting devices, e.g., one or more light emitting diodes. 
     BACKGROUND 
     There is an ongoing effort to develop systems that are more energy-efficient. A large proportion (some estimates are as high as twenty-five percent) of the electricity generated in the United States each year goes to lighting, a large portion of which is general illumination (e.g., downlights, flood lights, spotlights and other general residential or commercial illumination products). Accordingly, there is an ongoing need to provide lighting (of all types, including general illumination) that is more energy-efficient, without sacrificing other desired properties of lighting (or limiting detraction of other desired properties). 
     Solid state light emitters (e.g., light emitting diodes) are receiving much attention due to their energy efficiency. It is well known that incandescent light bulbs are very energy-inefficient light sources—about ninety percent of the electricity they consume is released as heat rather than light. Fluorescent light bulbs are more efficient than incandescent light bulbs (by a factor of about 10) but are still less efficient than solid state light emitters, such as light emitting diodes. 
     In addition, as compared to the normal lifetimes of solid state light emitters, e.g., light emitting diodes, incandescent light bulbs have relatively short lifetimes, i.e., typically about 750-1000 hours. In comparison, light emitting diodes, for example, have typical lifetimes between 50,000 and 70,000 hours. Fluorescent bulbs have longer lifetimes (e.g., 10,000-20,000 hours) than incandescent lights, but provide less favorable color reproduction. The typical lifetime of conventional fixtures is about 20 years, corresponding to a light-producing device usage of at least about 44,000 hours (based on usage of 6 hours per day for 20 years). Where the light-producing device lifetime of the light emitter is less than the lifetime of the fixture, the need for periodic change-outs is presented. The impact of the need to replace light emitters is particularly pronounced where access is difficult (e.g., vaulted ceilings, bridges, high buildings, highway tunnels) and/or where change-out costs are extremely high. 
     General illumination devices are typically rated in terms of their color reproduction. Color reproduction is typically measured using the Color Rendering Index (CRI Ra). CRI Ra is a modified average of the relative measurements of how the color rendition of an illumination system compares to that of a reference radiator when illuminating eight reference colors, i.e., it is a relative measure of the shift in surface color of an object when lit by a particular lamp. The CRI Ra equals 100 if the color coordinates of a set of test colors being illuminated by the illumination system are the same as the coordinates of the same test colors being irradiated by the reference radiator. 
     Daylight has a high CRI (Ra of approximately 100), with incandescent bulbs also being relatively close (Ra greater than 95), and fluorescent lighting being less accurate (typical Ra of 70-80). Certain types of specialized lighting have very low CRI (e.g., mercury vapor or sodium lamps have Ra as low as about 40 or even lower). Sodium lights are used, e.g., to light highways—driver response time, however, significantly decreases with lower CRI Ra values (for any given brightness, legibility decreases with lower CRI Ra). 
     The color of visible light output by a light emitter, and/or the color of blended visible light output by a plurality of light emitters can be represented on either the 1931 CIE (Commission International de I&#39;Eclairage) Chromaticity Diagram or the 1976 CIE Chromaticity Diagram. Persons of skill in the art are familiar with these diagrams, and these diagrams are readily available (e.g., by searching “CIE Chromaticity Diagram” on the internet). 
     The CIE Chromaticity Diagrams map out the human color perception in terms of two CIE parameters x and y (in the case of the 1931 diagram) or u′ and v′ (in the case of the 1976 diagram). Each point (i.e., each “color point”) on the respective Diagrams corresponds to a particular color. For a technical description of CIE chromaticity diagrams, see, for example, “Encyclopedia of Physical Science and Technology”, vol. 7, 230-231 (Robert A Meyers ed., 1987). The spectral colors are distributed around the boundary of the outlined space, which includes all of the hues perceived by the human eye. The boundary represents maximum saturation for the spectral colors. 
     The 1931 CIE Chromaticity Diagram can be used to define colors as weighted sums of different hues. The 1976 CIE Chromaticity Diagram is similar to the 1931 Diagram, except that similar distances on the 1976 Diagram represent similar perceived differences in color. 
     In the 1931 Diagram, deviation from a point on the Diagram (i.e., “color point”) can be expressed either in terms of the x, y coordinates or, alternatively, in order to give an indication as to the extent of the perceived difference in color, in terms of MacAdam ellipses. For example, a locus of points defined as being ten MacAdam ellipses from a specified hue defined by a particular set of coordinates on the 1931 Diagram consists of hues that would each be perceived as differing from the specified hue to a common extent (and likewise for loci of points defined as being spaced from a particular hue by other quantities of MacAdam ellipses). 
     Since similar distances on the 1976 Diagram represent similar perceived differences in color, deviation from a point on the 1976 Diagram can be expressed in terms of the coordinates, u′ and v′, e.g., distance from the point=(Δu′ 2 +Δv′ 2 ) 1/2 . This formula gives a value, in the scale of the u′ v′ coordinates, corresponding to the distance between points. The hues defined by a locus of points that are each a common distance from a specified color point consist of hues that would each be perceived as differing from the specified hue to a common extent. 
     A series of points that is commonly represented on the CIE Diagrams is referred to as the blackbody locus. The chromaticity coordinates (i.e., color points) that lie along the blackbody locus obey Planck&#39;s equation: E(λ)=Aλ −5 /(e B/T )−1), where E is the emission intensity, λ is the emission wavelength, T is the color temperature of the blackbody and A and B are constants. The 1976 CIF, Diagram includes temperature listings along the blackbody locus. These temperature listings show the color path of a blackbody radiator that is caused to increase to such temperatures. As a heated object becomes incandescent, it first glows reddish, then yellowish, then white, and finally blueish. This occurs because the wavelength associated with the peak radiation of the blackbody radiator becomes progressively shorter with increased temperature, consistent with the Wien Displacement Law. Illuminants that produce light that is on or near the blackbody locus can thus be described in terms of their color temperature. 
     The most common type of general illumination is white light (or near white light), i.e., light that is close to the blackbody locus, e.g., within about 10 MacAdam ellipses of the blackbody locus on a 1931 CIE Chromaticity Diagram. Light with such proximity to the blackbody locus is referred to as “white” light in terms of its illumination, even though some light that is within 10 MacAdam ellipses of the blackbody locus is tinted to some degree, e.g., light from incandescent bulbs is called “white” even though it sometimes has a golden or reddish tint; also, if the light having a correlated color temperature of 1500 K or less is excluded, the very red light along the blackbody locus is excluded. 
     The emission spectrum of any particular light emitting diode is typically concentrated around a single wavelength (as dictated by the light emitting diode&#39;s composition and structure), which is desirable for some applications, but not desirable for others, (e.g., for providing general illumination, such an emission spectrum provides a very low CRI Ra). 
     Because light that is perceived as white is necessarily a blend of light of two or more colors (or wavelengths), no single light emitting diode junction has been developed that can produce white light. 
     “White” solid state light emitting lamps have been produced by providing devices that mix different colors of light, e.g., by using light emitting diodes that emit light of differing respective colors and/or by converting some or all of the light emitted from the light emitting diodes using luminescent material. For example, as is well known, some lamps (referred to as “RGB lamps”) use red, green and blue light emitting diodes, and other lamps use (1) one or more light emitting diodes that generate blue light and (2) luminescent material (e.g., one or more phosphor materials) that emits yellow light in response to excitation by light emitted by the light emitting diode, whereby the blue light and the yellow light, when mixed, produce light that is perceived as white light. While there is a need for more efficient white lighting, there is in general a need for more efficient lighting in all hues. 
     There are many situations where it is desired for the intensity of light exiting a lighting device to be highly uniform. For instance, with general illumination devices, it is often desired to have a lighting device where the variance of intensity between different locations from which light exits the lighting device (e.g., the lens) is limited or minimized. The challenges presented by a desire for uniformity can be increased where the size of the region from which light is emitted is increased, e.g., in the case of troffer lights, which are often designed to fit in square spaces in ceilings measuring roughly two feet by two feet or in rectangular spaces in ceilings measuring roughly two feet by four feet. 
     There are many situations where it is desired for the light exiting a lighting device to create less glare. Again, such challenges can be more pronounced with lights having larger areas of light emission. 
     For the above and other reasons, there is an ongoing need for a lighting device that provides good efficiency, good color uniformity of emitted light, good intensity uniformity of emitted light, and/or low glare. In some cases, it is further desired that the light emitted from the lighting device be white and have acceptable color temperature and/or high CRI Ra, and/or that the lighting device have a long useful life. 
     BRIEF SUMMARY OF THE INVENTIVE SUBJECT MATTER 
     Excellent uniformity of light level across a surface of emission for a lighting device can be achieved in accordance with the present inventive subject matter by providing a combination of (1) at least one luminescent material that is spaced from light sources, and (2) at least one light control element. Excellent uniformity of light level and color can be achieved in accordance with the present inventive subject matter even where the source (or sources) of light within the lighting device comprises one or more solid state light emitters, for example, light emitting diodes that respectively emit light of at least two different colors (such as blue and red). 
     In one aspect of the present inventive subject matter, there is provided a lighting device that comprises at least one light control element. 
     In another aspect of the present inventive subject matter, there is provided a lighting device that comprises a first light source and at least a first luminescent material that is spaced from the first light source. 
     In another aspect of the present inventive subject matter, there is provided a lighting device that comprises a first luminescent material and at least one light control element. 
     In another aspect of the present inventive subject matter, there is provided a lighting device that comprises a first light source, a first luminescent material and at least one light control element. 
     In another aspect of the present inventive subject matter, there is provided a lighting device, comprising: 
     at least a first light control element; 
     at least a first light source positioned so that at least a portion of light emitted by the first light source passes through at least a portion of the first light control element; and 
     at least a first luminescent material, at least a portion of the first luminescent material being spaced from the first light source, the first luminescent material being positioned so that at least a portion of light emitted by the first light source excites at least a portion of the first luminescent material. 
     In some embodiments according to the present inventive subject matter, the lighting device further comprises at least a first light control element which comprises one or more volumetric light control structure and/or one or more surface light control feature. In some of such embodiments, at least a portion of the first luminescent material is positioned on at least one surface of the first light control element and/or within the first light control element. 
     The inventive subject matter may be more fully understood with reference to the accompanying drawings and the following detailed description of the inventive subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         FIG. 1  is a cross-sectional view of a lighting device  10  according to the present inventive subject matter. 
         FIG. 2  is a perspective view of the lighting device  10  of  FIG. 1 . 
         FIG. 3  depicts a representative example of a cover element that comprises a light control element for use in lighting devices according to the present inventive subject matter. 
         FIG. 4  depicts a representative example of a cover element that comprises a light control element for use in lighting devices according to the present inventive subject matter. 
         FIG. 5  depicts a representative example of a cover element that comprises a light control element for use in lighting devices according to the present inventive subject matter. 
         FIG. 6  depicts a representative example of a cover element that comprises a light control element for use in lighting devices according to the present inventive subject matter. 
         FIG. 7  is a cross-sectional view of a lighting device  40  according to the present inventive subject matter. 
         FIG. 8  is a bottom view of the lighting device  40  of  FIG. 7 . 
         FIG. 9  is a schematic diagram of a lighting device  150  according to the inventive subject matter. 
         FIG. 10  illustrates a lighting device  50  in accordance with the present inventive subject matter. 
         FIG. 11  is a sectional view of the lighting device  50  taken along the plane  11 - 11 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTIVE SUBJECT MATTER 
     The present inventive subject matter now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the inventive subject matter are shown. However, this inventive subject matter should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive subject matter to those skilled in the art. Like numbers refer to like elements throughout. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items. All numerical quantities described herein are approximate and should not be deemed to be exact unless so stated. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the inventive subject matter. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     When an element such as a layer, region or substrate is referred to herein as being “on”, being mounted “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to herein as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Also, when an element is referred to herein as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to herein as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. In addition, a statement that a first element is “on” a second element is synonymous with a statement that the second element is “on” the first element. 
     The expression “in contact with”, as used herein, means that the first structure that is in contact with a second structure is in direct contact with the second structure or is in indirect contact with the second structure. The expression “in indirect contact with” means that the first structure is not in direct contact with the second structure, but that there are a plurality of structures (including the first and second structures), and each of the plurality of structures is in direct contact with at least one other of the plurality of structures (e.g., the first and second structures are in a stack and are separated by one or more intervening layers). The expression “direct contact”, as used in the present specification, means that the first structure which is “in direct contact” with a second structure is touching the second structure and there are no intervening structures between the first and second structures at least at some location. 
     Although the terms “first”, “second”, etc. may be used herein to describe various elements, components, regions, layers, sections and/or parameters, these elements, components, regions, layers, sections and/or parameters should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present inventive subject matter. 
     Relative terms, such as “lower”, “bottom”, “below”, “upper”, “top” or “above,” may be used herein to describe one element&#39;s relationship to another elements as illustrated in the Figures. Such relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in the Figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower”, can therefore, encompass both an orientation of “lower” and “upper,” depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below. 
     The term “illumination” (or “illuminated”), as used herein means that a light source is emitting electromagnetic radiation. For example, the term “illumination” means that at least some current is being supplied to the light source to cause the light source to emit at least some electromagnetic radiation (in some cases, with at least a portion of the emitted radiation having a wavelength between 100 nm and 1000 nm, and in some cases within the visible spectrum). The expression “illuminated” also encompasses situations where the light source emits light continuously or intermittently at a rate such that if it is or was visible light, a human eye would perceive it as emitting light continuously (or discontinuously), or where a plurality of light sources (especially in the case of solid state light emitters) that emit light of the same color or different colors are emitting light intermittently and/or alternatingly (with or without overlap in “on” times) in such a way that if they were or are visible light, a human eye would perceive them as emitting light continuously or discontinuously (and, in some cases where different colors are emitted, as separate colors or as a mixture of those colors). 
     The expression “excited”, as used herein when referring to luminescent material, means that at least some electromagnetic radiation (e.g., visible light, UV light or infrared light) is contacting the luminescent material, causing the luminescent material to emit at least some light. The expression “excited” encompasses situations where the luminescent material emits light continuously, or intermittently at a rate such that a human eye would perceive it as emitting light continuously or intermittently, or where a plurality of luminescent materials of the same color or different colors are emitting light intermittently and/or alternatingly (with or without overlap in “on” times) in such a way that a human eye would perceive them as emitting light continuously or intermittently (and, in some cases where different colors are emitted, as a mixture of those colors). 
     The expression “lighting device”, as used herein, is not limited, except that it indicates that the device is capable of emitting light. That is, a lighting device can be a device which illuminates an area or volume, e.g., a structure, a swimming pool or spa, a room, a warehouse, an indicator, a road, a parking lot, a vehicle, signage, e.g., road signs, a billboard, a ship, a toy, a mirror, a vessel, an electronic device, a boat, an aircraft, a stadium, a computer, a remote audio device, a remote video device, a cell phone, a tree, a window, an LCD display, a cave, a tunnel, a yard, a lamppost, or a device or array of devices that illuminate an enclosure, or a device that is used for edge or back-lighting (e.g., back light poster, signage, LCD displays), bulb replacements (e.g., for replacing AC incandescent lights, low voltage lights, fluorescent lights, etc.), lights used for outdoor lighting, lights used for security lighting, lights used for exterior residential lighting (wall mounts, post/column mounts), ceiling fixtures/wall sconces, under cabinet lighting, lamps (floor and/or table and/or desk), landscape lighting, track lighting, task lighting, specialty lighting, ceiling fan lighting, archival/art display lighting, high vibration/impact lighting-work lights, etc., mirrors/vanity lighting, or any other light emitting device. 
     The expression “major surface” as used herein, means a surface which has a surface area which comprises at least 25% of the surface area of the entire structure, and in some cases at least 40% of the surface area of the entire structure (e.g., each of the top and bottom surfaces of a substantially flat thin substrate having substantially parallel top and bottom surfaces). 
     The present inventive subject matter further relates to an illuminated enclosure (the volume of which can be illuminated uniformly or non-uniformly), comprising an enclosed space and at least one lighting device according to the present inventive subject matter, wherein the lighting device illuminates at least a portion of the enclosed space (uniformly or non-uniformly). 
     Some embodiments of the present inventive subject matter comprise at least a first power line, and some embodiments of the present inventive subject matter are directed to a structure comprising a surface and at least one lighting device corresponding to any embodiment of a lighting device according to the present inventive subject matter as described herein, wherein if current is supplied to the first power line, and/or if at least one light source in the lighting device is illuminated, the lighting device would illuminate at least a portion of the surface. 
     The present inventive subject matter is further directed to an illuminated area, comprising at least one item, e.g., selected from among the group consisting of a structure, a swimming pool or spa, a room, a warehouse, an indicator, a road, a parking lot, a vehicle, signage, e.g., road signs, a billboard, a ship, a toy, a mirror, a vessel, an electronic device, a boat, an aircraft, a stadium, a computer, a remote audio device, a remote video device, a cell phone, a tree, a window, an LCD display, a cave, a tunnel, a yard, a lamppost, etc., having mounted therein or thereon at least one lighting device as described herein. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive subject matter belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed “adjacent” another feature may have portions that overlap or underlie the adjacent feature. 
     The expression “substantially square”, as used herein, means that the shape can be placed on x,y coordinates such that at least 90 percent of the points on the shape have an x coordinate or a y coordinate which is within 0.95 to 1.05 times a particular value or the negative of that value, and the absolute value of neither the x coordinate nor the y coordinate exceeds the absolute value of 1.05 times such particular value. 
     The expression “substantially rectangular”, as used herein, means that a rectangular shape can be identified, wherein at least 90% of the points in the item which is characterized as being substantially rectangular fall within the rectangular shape, and the rectangular shape includes at least 90% of the point in the item. 
     The expression “substantially circular”, as used herein, means that a circle can be drawn having the formula x 2 +y 2 =n, where imaginary axes could be drawn at a location where for each of at least 80% of the points on the feature being characterized as “substantially circular”, the y coordinate would be within 0.95 to 1.05 times the value obtained by inserting the x coordinate of such point into such formula. 
     In one aspect of the present inventive subject matter, there is provided a lighting device, comprising at least a first light control element, at least a first light source and at least a first luminescent material. 
     The one or more light control element (or elements) employed in lighting devices according to the present inventive subject matter can be any structure or feature that alters the overall nature of the pattern formed by light emitted by the first light source. As such, the expression “light control element”, as used herein, encompasses films and lenses which comprise one or more volumetric light control structures and/or one or more surface light control features. While films and/or lenses which are merely of indices of refraction that differ from those of adjacent regions, and/or which merely alter the focus of light and/or which assist in diffusion (color mixing) and/or obscuration (depixelization), and/or which are of a substantially uniform thickness or mean thickness, can be included in the lighting devices according to the present inventive subject matter (and in many cases are desired), such films and/or lenses are not encompassed by the expression “light control element” as used herein. In some aspects of the present inventive subject matter, the one or more light control elements are non-imaging optics, i.e., they include diffusers and light shapers/lamp hiders (like acrylic prismatic sheets) and exclude imaging optics (e.g., optics used in telescopes and cameras). 
     As is well known by persons of skill in the art, light control elements can be in any of a variety of forms, and any suitable ones of such forms can be employed in accordance with the present inventive subject matter. For example, as mentioned above, a light control element can comprise one or more volumetric light control structures and/or one or more surface light control features. A volumetric light control structure is one in which the light control is achieved by regions extending through at least part of the thickness or depth of the light control structure. Persons of skill in the art are familiar with, for example, light control structures in which lenslets are made in at least part of the volume of a structure, e.g., in which diffusion elements are contained within pellets, which are worked in bulk and later molded (e.g., injection molded) or extruded. Likewise, light control can be provided by regions in at least part of the thickness or depth of a film (as is known to those of skill in the art, such films are contrasted with molded or extruded lenses in that such films, e.g., several thousandths of an inch up to 10 or 20 thousandths of an inch, cannot be scaled up to significantly larger thicknesses). As an example of a method of making such a film, a base stock can be mixed with a material (or materials) of index of refraction that differs from that of the base stock to form a controlled dispersion, which is then extruded. 
     A surface light control feature, as contrasted from a volumetric light control structure, is a surface feature, i.e., it is formed on a surface of a structure, e.g., a lens or a film. Persons of skill in the art are familiar with a variety of surface light control features and ways to provide them. Representative examples of ways to provide surface light control features include mechanically pressing a film or a lens, molding surface light control features (e.g., injection molding using a mold which has surface features that will impart in the injection molded structures one or more surface light control features), and patterning (e.g., by photolithography) on a film or lens (patterning by photolithography is typically used on films, but it could be used on lenses, if desired). 
     With respect to light control elements that comprise one or more volumetric light control structures, the light control structure(s) can be located in any suitable portion of the light control element, e.g., the top half, the bottom half, substantially the entirety, or any other portion. With respect to light control elements that comprise one or more surface features, the surface feature(s) can be located on either (or both) sides of the light control element, and can extend across any portion (or substantially all) of such surface(s). 
     Persons of skill in the art are also familiar with a variety of light control feature effects. For example, one well known type of light control effect is collimation (also known as beam shaping), the broadest sense of which is affecting the direction in which a significant portion of light travels. One example of a type of collimation is where a significant portion (e.g., at least 50%, in some cases at least 60%, and in some cases at least 70%, 80%, 90%, 95%, 99% or more) of incident light is caused to travel substantially perpendicularly to a surface of the light control element. For example, one of the first types of light control element was designed to transmit a larger percentage of light traveling in a direction substantially perpendicular to a surface of the structure facing the light than the percentage of light traveling in a direction that defines an angle of less than 45 degrees relative to the surface of the structure facing the light (in other words, with such elements, light that strikes the light control element perpendicularly is more likely to pass through the light control element than light that strikes the light control element obliquely). Another well known type of light control effect is distribution, i.e., affecting the amount of light that goes to a given region. For example, one example of a type of light control distribution effect is referred to as a “bat wing distribution”, where comparatively less light is directed to a location directly below the lighting device and comparatively more light is directed to locations spaced from directly below the lighting device (or to only one side of a location directly below the lighting device, or to only two sides of such location, etc.), e.g., to counteract the effect, caused by intensity falling as the square of the distance, of light being comparatively brighter directly below the lighting device (and sometimes at locations near locations that are directly below the lighting device). 
     The one or more light control elements can be formed of any material (or materials) and can be of any size and shape, so long as it alters the overall nature of the pattern formed by light emitted by at least the first light source. 
     In some embodiments, the light control element has first and second major surfaces that are substantially parallel to each other, and the light control element has a thickness (i.e., a dimension substantially perpendicular to the first and second major surfaces) that is much smaller than the dimensions of the major surfaces, e.g., less than one fifth (and in some embodiments, less than one tenth or less than one twentieth) of a dimension of one or both of the major surfaces. 
     The light control element (or elements) used in the lighting devices according to the present inventive subject matter can also be selected from among any of the known light control elements. Representative examples of suitable light control elements includes those disclosed in U.S. Pat. No. 5,147,716 and U.S. Patent Application Publication No. 2009/0115943, the entireties of which are hereby incorporated by reference as if set forth in their entirety. 
     Each of the one or more light sources can be selected from among any or all of the wide variety of light sources known to persons of skill in the art. Representative examples of types of light sources include incandescent lights, fluorescent lamps, solid state light emitters, laser diodes, thin film electroluminescent devices, light emitting polymers (LEPs), halogen lamps, high intensity discharge lamps, electron-stimulated luminescence lamps, etc., each with or without one or more filters. That is, the at least one light source can comprise a single light source, a plurality of light sources of a particular type, or any combination of one or more light sources of each of a plurality of types. 
     A variety of solid state light emitters are well known, and any of such light emitters can be employed according to the present inventive subject matter. Representative examples of solid state light emitters include light emitting diodes (inorganic or organic, including polymer light emitting diodes (PLEDs)) with or without luminescent materials. 
     Light emitting diodes are semiconductor devices that convert electrical current into light. A wide variety of light emitting diodes are used in increasingly diverse fields for an ever-expanding range of purposes. More specifically, light emitting diodes are semiconducting devices that emit light (ultraviolet, visible, or infrared) when a potential difference is applied across a p-n junction structure. There are a number of well-known ways to make light emitting diodes and many associated structures, and the present inventive subject matter can employ any such devices. 
     A light emitting diode produces light by exciting electrons across the band gap between a conduction band and a valence band of a semiconductor active (light-emitting) layer. The electron transition generates light at a wavelength that depends on the band gap. Thus, the color of the light (wavelength) emitted by a light emitting diode depends on the semiconductor materials of the active layers of the light emitting diode. 
     The expression “light emitting diode” is used herein to refer to the basic semiconductor diode structure (i.e., the chip). The commonly recognized and commercially available “LED” that is sold (for example) in electronics stores typically represents a “packaged” device made up of a number of parts. These packaged devices typically include a semiconductor based light emitting diode such as (but not limited to) those described in U.S. Pat. Nos. 4,918,487; 5,631,190; and 5,912,477; various wire connections, and a package that encapsulates the light emitting diode. 
     Persons of skill in the art are familiar with, and have ready access to, a variety of solid state light emitters that emit light having a desired peak emission wavelength and/or dominant emission wavelength, and any of such solid state light emitters (discussed in more detail below), or any combinations of such solid state light emitters, can be employed in embodiments that comprise a solid state light emitter. 
     A luminescent material is a material that emits a responsive radiation (e.g., visible light) when excited by a source of exciting radiation. In many instances, the responsive radiation has a wavelength which is different from the wavelength of the exciting radiation. 
     Luminescent materials can be categorized as being down-converting, i.e., a material which converts photons to a lower energy level (longer wavelength) or up-converting, i.e., a material which converts photons to a higher energy level (shorter wavelength). 
     Persons of skill in the art are familiar with, and have ready access to, a variety of luminescent materials that emit light having a desired peak emission wavelength and/or dominant emission wavelength, or a desired hue, and any of such luminescent materials, or any combinations of such luminescent materials, can be employed, if desired. 
     One type of luminescent material are phosphors, which are readily available and well known to persons of skill in the art. Other examples of luminescent materials include scintillators, day glow tapes and inks which glow in the visible spectrum upon illumination with ultraviolet light. 
     The advantage of providing a wider spectrum of visible wavelengths to provide increased CRI (e.g., Ra) is well known, and the ability to predict the perceived color of output light from a lighting device which includes light emitters which output two or more respective colors of light is also well known, e.g., with the assistance of the CIE color charts. 
     Luminescent material (when included) can be provided in any suitable form. For example, the luminescent element can be embedded in the heat dissipation element and/or in a resin (i.e., a polymeric matrix), such as a silicone material, an epoxy material, a glass material or a metal oxide material. The luminescent material can be contained in an encapsulant in which one or more light source (e.g., a light emitting diode) is embedded. 
     Representative examples of suitable solid state light emitters, including suitable light emitting diodes, luminescent materials, lumiphors, encapsulants, etc. that may be used in practicing the present inventive subject matter, are described in: 
     U.S. patent application Ser. No. 11/614,180, filed Dec. 21, 2006 (now U.S. Patent Publication No. 2007/0236911), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/624,811, filed Jan. 19, 2007 (now U.S. Patent Publication No. 2007/0170447), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/751,982, filed May 22, 2007 (now U.S. Patent Publication No. 2007/0274080), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/753,103, filed May 24, 2007 (now U.S. Patent Publication No. 2007/0280624), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/751,990, filed May 22, 2007 (now U.S. Patent Publication No. 2007/0274063), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/736,761, filed Apr. 18, 2007 (now U.S. Patent Publication No. 2007/0278934), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/936,163, filed Nov. 7, 2007 (now U.S. Patent Publication No. 2008/0106895), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/843,243, filed Aug. 22, 2007 (now U.S. Patent Publication No. 2008/0084685), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/870,679, filed Oct. 11, 2007 (now U.S. Patent Publication No. 2008/0089053), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/117,148, filed May 8, 2008 (now U.S. Patent Publication No. 2008/0304261), the entirety of which is hereby incorporated by reference as if set forth in its entirety; and 
     U.S. patent application Ser. No. 12/017,676, filed on Jan. 22, 2008 (now U.S. Patent Publication No. 2009-0108269), the entirety of which is hereby incorporated by reference as if set forth in its entirety. 
     Each of the one or more light sources can be of any suitable shape, a variety of which are known to those of skill in the art, e.g., in the shape of an A lamp, a B-10 lamp, a BR lamp, a C-7 lamp, a C-15 lamp, an ER lamp, an F lamp, a G lamp, a K lamp, an MB lamp, an MR lamp, a PAR lamp, a PS lamp, an R lamp, an S lamp, an S-11 lamp, a T lamp, a Linestra 2-base lamp, an AR lamp, an ED lamp, an E lamp, a BT lamp, a Linear fluorescent lamp, a U-shape fluorescent lamp, a circline fluorescent lamp, a single twin tube compact fluorescent lamp, a double twin tube compact fluorescent lamp, a triple twin tube compact fluorescent lamp, an A-line compact fluorescent lamp, a screw twist compact fluorescent lamp, a globe screw base compact fluorescent lamp, or a reflector screw base compact fluorescent lamp. Lighting devices according to the present inventive subject matter can comprise one or more light sources of a particular shape or one or more light sources of each of a plurality of different shapes. 
     Each of the one or more light sources can be designed to emit light in any suitable pattern, e.g., in the form of a flood light, a spotlight, a downlight, etc. Lighting devices according to the present inventive subject matter can comprise one or more light sources that emit light in any suitable pattern, or one or more light sources that emit light in each of a plurality of different patterns. 
     At least a portion of the first luminescent material is spaced from the first light source. The term “spaced”, as used herein, means that the first luminescent material is not in direct contact with the first light source. In some embodiments, the first luminescent material is not in direct or indirect contact with the first light source. In some embodiments, the first luminescent material is spaced from the first light source by a distance that is at least as large (and in some embodiments twice as large, and in some embodiments, three, four, five or ten times as large) as a largest dimension of an emission surface of the first light source. In some embodiments, the first luminescent material is spaced from the first light source by at least 30 percent of a smallest dimension of the lighting device. 
     For example, luminescent material can be provided in or on any suitable element (or elements) in the lighting device. In some embodiments, for instance, luminescent material can be provided in or on a light control element, in or on a diffusion element, in or on an obscuration element, in or on a housing member, in or on a reflector, etc. In embodiments where luminescent material is provided on a surface of a light control element, the luminescent material can be provided on either (or both) surfaces. In some embodiments, for example, luminescent material can be provided on a side (the “smooth side”) of the light control element that faces the light source(s) (e.g., one or more light emitting diodes), and a surface light control feature can be provided on a side (the “fuzzy side”) of the light control element that faces away from the light source(s). 
     In general, light of any combination and number of colors can be mixed in lighting devices according to the present inventive subject matter. Representative examples of blends of light colors are described in: 
     U.S. patent application Ser. No. 11/613,714, filed Dec. 20, 2006 (now U.S. Patent Publication No. 2007/0139920), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/613,733, filed Dec. 20, 2006 (now U.S. Patent Publication No. 2007/0137074), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/736,761, filed Apr. 18, 2007 (now U.S. Patent Publication No. 2007/0278934), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/736,799, filed Apr. 18, 2007 (now U.S. Patent Publication No. 2007/0267983), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/737,321, filed Apr. 19, 2007 (now U.S. Patent Publication No. 2007/0278503), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/936,163, filed Nov. 7, 2007 (now U.S. Patent Publication No. 2008/0106895), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/117,122, filed May 8, 2008 (now U.S. Patent Publication No. 2008/0304260), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/117,131, filed May 8, 2008 (now U.S. Patent Publication No. 2008/0278940), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/117,136, filed May 8, 2008 (now U.S. Patent Publication No. 2008/0278928), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. Pat. No. 7,213,940, issued on May 8, 2007, the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. Patent Application No. 60/868,134, filed on Dec. 1, 2006, entitled “LIGHTING DEVICE AND LIGHTING METHOD” (inventors: Antony Paul van de Ven and Gerald H. Negley), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/948,021, filed on Nov. 30, 2007 (now U.S. Patent Publication No. 2008/0130285), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/248,220, filed on Oct. 9, 2008 (now U.S. Patent Publication No. 2009/0184616), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/951,626, filed Dec. 6, 2007 (now U.S. Patent Publication No. 2008/0136313), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/035,604, filed on Feb. 22, 2008 (now U.S. Patent Publication No. 2008/0259589), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/117,148, filed May 8, 2008 (now U.S. Patent Publication No. 2008/0304261), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. Patent Application No. 60/990,435, filed on Nov. 27, 2007, entitled “WARM WHITE ILLUMINATION WITH HIGH CRI AND HIGH EFFICACY” (inventors: Antony Paul van de Ven and Gerald H. Negley), the entirety of which is hereby incorporated by reference as if set forth in its entirety; and 
     U.S. patent application Ser. No. 12/541,215, filed Aug. 14, 2009, (now U.S. Patent Publication No. 2011/0037409), the entirety of which is hereby incorporated by reference as if set forth in its entirety. 
     In some embodiments according to the present inventive subject matter, the lighting devices can further comprise one or more sensors. 
     Persons of skill in the art are familiar with a wide variety of sensors, and any of such sensors can be employed in the lighting devices of the present inventive subject matter. Among these well known sensors are sensors that are sensitive to all visible light, as well as sensors that are sensitive to only a portion of visible light. For example, the sensor can be a unique and inexpensive sensor (GaP:N light emitting diode) that views the entire light flux but is only (optically) sensitive to one or more of a plurality of light emitting diodes. For instance, in one specific example, the sensor can be sensitive to only a particular range (or ranges) of wavelengths, and the sensor can provide feedback to one or more light sources (e.g., light emitting diodes that emit light of that color or that emit light of other colors) for color consistency as the light sources age (and light output decreases). By using a sensor that monitors output selectively (by color), the output of one color can be selectively controlled to maintain the proper ratios of outputs and thereby maintain the color temperature of the device. This type of sensor is excited by only light having wavelengths within a particular range, e.g., a range that excludes red light (see, e.g., U.S. patent application Ser. No. 12/117,280, filed May 8, 2008 (now U.S. Patent Publication No. 2008/0309255), the entirety of which is hereby incorporated by reference as if set forth in its entirety. 
     In some embodiments according to the present inventive subject matter, the lighting device further comprises a sensor that detects an intensity of light emitted by one or more strings of light sources (e.g., light emitting diodes) (the expression “string”, as used herein, means that at least two light sources are electrically connected in series), and circuitry that adjusts a current supplied to such one or more strings of light sources in response to that intensity. Persons of skill in the art are familiar with a variety of sensors that can detect an intensity of light emitted by one or more light sources, and any of such sensors can be used in making such embodiments. Similarly, persons of skill in the art are familiar with a variety of types of circuitry that can adjust a current supplied to one or more strings of light sources (or adjust currents supplied independently to each of plural strings of light sources) in response to any signal or command (e.g., intensity detected by the sensor(s)), and any of such types of circuitry can be employed in the devices according to the present inventive subject matter. For example, in some embodiments according to the present inventive subject matter, the current supplied to a third string of solid state lighting devices can be set to a particular value for the intensity of the combined light emitted by the solid state lighting devices in first and second strings of solid state lighting devices as detected during testing (i.e., their initial combined intensity), and the current supplied to the third string can be varied (linearly or non-linearly) from that set value in response to variance in the intensity of the combined light emitted by the solid state lighting devices in the first and second strings of solid state lighting devices over time (e.g., as the intensity of the solid state lighting devices in the first and second strings of solid state lighting devices decreases over time, the current supplied to the third string of solid state lighting devices can be varied in order to reduce or minimize deviation of the combined color output of the lighting device over time). Skilled artisans are familiar with a variety of ways to provide such a relationship, e.g., by providing a sensor feedback that, in response to variances in the intensity of the combined light emitted by the light sources in the first and second strings, adjusts a reference voltage for the third string. 
     Some embodiments of the present inventive subject matter include measuring color output of a lighting device while supplying current to one or more strings of light sources, and adjusting the current supplied to at least one of the first string of light sources. Persons of skill in the art are familiar with a variety of devices and techniques for measuring color output, and any of such devices and techniques can be employed in the devices according to the present inventive subject matter. Similarly, persons of skill in the art are familiar with a wide variety of devices and techniques for adjusting current supplied to one or more strings of light sources, and any of such devices and techniques can be employed in the devices according to the present inventive subject matter. Thus, the currents are tunable based upon characteristics of the specific device (and components thereof) being used. 
     Other techniques for sensing changes in light output of light sources include providing separate or reference emitters and a sensor that measures the light output of these emitters. These reference emitters are placed so as to be isolated from ambient light such that they typically do not contribute to the light output of the lighting device. Additional techniques for sensing the light output of a light source include measuring ambient light and light output of the lighting device separately and then compensating the measured light output of the light source based on the measured ambient light. 
     Some embodiments in accordance with the present inventive subject matter can employ at least one temperature sensor. Persons of skill in the art are familiar with, and have ready access to, a variety of temperature sensors (e.g., thermistors), and any of such temperature sensors can be employed in embodiments in accordance with the present inventive subject matter. Temperature sensors can be used for a variety of purposes, e.g., to provide feedback information to current adjusters, as described in U.S. patent application Ser. No. 12/117,280, filed May 8, 2008 (now U.S. Patent Publication No. 2008/0309255), the entirety of which is hereby incorporated by reference as if set forth in its entirety. 
     In accordance with some embodiments of the present inventive subject matter, there are provided devices that comprise a controller configured to control a ratio of light emitted by at least one light source and light emitted by at least a second light source such that a combination of light is a desired color (e.g., white). 
     Persons of skill in the art are familiar with, have access to, and can readily envision a variety of suitable controllers. For example, a controller may be a digital controller, an analog controller or a combination of digital and analog. For example, the controller may be an application specific integrated circuit (ASIC), a microprocessor, a microcontroller, a collection of discrete components or combinations thereof. In some embodiments, the controller may be programmed to control the one or more light sources. In some embodiments, control of the one or more light sources may be provided by the circuit design of the controller and is, therefore, fixed at the time of manufacture. In still further embodiments, aspects of the controller circuit, such as reference voltages, resistance values or the like, may be set at the time of manufacture so as to allow adjustment of the control of the one or more light sources without the need for programming or control code. 
     Representative examples of suitable controllers are described in: 
     U.S. patent application Ser. No. 11/755,149, filed May 30, 2007 (now U.S. Patent Publication No. 2007/0278974), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/117,280, filed May 8, 2008 (now U.S. Patent Publication No. 2008/0309255), the entirety of which is hereby incorporated by reference as if set forth in its entirety; and 
     U.S. patent application Ser. No. 12/257,804, filed on Oct. 24, 2008 (now U.S. Patent Publication No. 2009/0160363), the entirety of which is hereby incorporated by reference as if set forth in its entirety. 
     Some embodiments in accordance with the present inventive subject matter include one or more diffusion elements and/or one or more obscuration elements. Persons of skill in the art are familiar with a wide variety of diffusion elements (i.e., elements that assist in color mixing), and a wide variety of obscuration elements (i.e., volumetric regions and/or surface features), and can readily envision a variety of materials out of which a diffusion element or an obscuration element can be made, and are familiar with and/or can envision a wide variety of shapes that such elements can be. Any of such materials and/or shapes can be employed in a diffusion element and/or an obscuration element in an embodiment that includes such an element (or elements). As will be understood by persons skilled in the art, a diffusion element or an obscuration element according to the present inventive subject matter can be selected based on their respective effects on incident light. For example, a diffusion element can include features to diffuse or scatter light, such as scattering particles dispersed within the element (e.g., particles made from titanium dioxide, alumina, silicon carbide, gallium nitride, or glass micro spheres). 
     In embodiments in accordance with the present inventive subject matter that include a diffusion element (or plural diffusion elements), the diffusion element (or diffusion elements) can be positioned in any suitable location and orientation. In some embodiments in accordance with the present inventive subject matter, a diffusion element can be positioned adjacent to and covering an aperture of the lighting device. 
     In embodiments in accordance with the present inventive subject matter that include an obscuration element (or plural obscuration elements), the obscuration element (or obscuration elements) can be positioned in any suitable location and orientation. In some embodiments in accordance with the present inventive subject matter, an obscuration element can be positioned adjacent to and covering an aperture of the lighting device. 
     In some embodiments according to the present invention, two or more types of features can be provided in a single element. For example, a single structure can provide light control as well as diffusion and/or obscuration. Typically, where multiple types of features are provided in a single structure, different regions of the structure provide the different features, e.g., regions providing the different features are stacked on one another. 
     In some embodiments according to the present inventive subject matter, the lighting device further comprises a support on which the one or more light sources are mounted. In such embodiments, the support can be of made of any suitable material, and can be of any suitable size and shape. 
     The present inventive subject matter is also directed to a light fixture that comprises at least one lighting device as described herein. The light fixture can comprise a housing, a mounting structure, and/or an enclosing structure. Persons of skill in the art are familiar with, and can envision, a wide variety of materials out of which a fixture, a housing, a mounting structure and/or an enclosing structure can be constructed, and a wide variety of shapes for such a fixture, a housing, a mounting structure and/or an enclosing structure. A fixture, a housing, a mounting structure and/or an enclosing structure made of any of such materials and having any of such shapes can be employed in accordance with the present inventive subject matter. 
     For example, fixtures, housings, mounting structures and enclosing structures, and components or aspects thereof, that may be used in practicing the present inventive subject matter are described in: 
     U.S. patent application Ser. No. 11/613,692, filed Dec. 20, 2006 (now U.S. Patent Publication No. 2007/0139923), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/743,754, filed May 3, 2007 (now U.S. Patent Publication No. 2007/0263393), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/755,153, filed May 30, 2007 (now U.S. Patent Publication No. 2007/0279903), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/856,421, filed Sep. 17, 2007 (now U.S. Patent Publication No. 2008/0084700), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/859,048, filed Sep. 21, 2007 (now U.S. Patent Publication No. 2008/0084701), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/939,047, filed Nov. 13, 2007 (now U.S. Patent Publication No. 2008/0112183), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/939,052, filed Nov. 13, 2007 (now U.S. Patent Publication No. 2008/0112168), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/939,059, filed Nov. 13, 2007 (now U.S. Patent Publication No. 2008/0112170), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/877,038, filed Oct. 23, 2007 (now U.S. Patent Publication No. 2008/0106907), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. Patent Application No. 60/861,901, filed on Nov. 30, 2006, entitled “LED DOWNLIGHT WITH ACCESSORY ATTACHMENT” (inventors: Gary David Trott, Paul Kenneth Pickard and Ed Adams), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/948,041, filed Nov. 30, 2007 (now U.S. Patent Publication No. 2008/0137347), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/114,994, filed May 5, 2008 (now U.S. Patent Publication No. 2008/0304269), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/116,341, filed May 7, 2008 (now U.S. Patent Publication No. 2008/0278952), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/277,745, filed on Nov. 25, 2008 (now U.S. Patent Publication No. 2009-0161356), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/116,346, filed May 7, 2008 (now U.S. Patent Publication No. 2008/0278950), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/116,348, filed on May 7, 2008 (now U.S. Patent Publication No. 2008/0278957), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/512,653, filed on Jul. 30, 2009 (now U.S. Patent Publication No. 2010-0102697), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/469,819, filed on May 21, 2009 (now U.S. Patent Publication No. 2010-0102199), the entirety of which is hereby incorporated by reference as if set forth in its entirety; and 
     U.S. patent application Ser. No. 12/469,828, filed on May 21, 2009 (now U.S. Patent Publication No. 2010-0103678), the entirety of which is hereby incorporated by reference as if set forth in its entirety. 
     In some embodiments according to the present inventive subject matter, including some embodiments that include or do not include any of the features as discussed above, the lighting device further comprises circuitry that delivers current from at least one energy source to the light source (or sources). 
     In some lighting devices according to the present inventive subject matter, there are further included one or more circuitry components, e.g., drive electronics for supplying and controlling current passed through the light source (or sources) in the lighting device. Persons of skill in the art are familiar with a wide variety of ways to supply and control the current passed through light sources, e.g., solid state light emitters, and any such ways can be employed in the devices of the present inventive subject matter. For example, such circuitry can include at least one contact, at least one leadframe, at least one current regulator, at least one power control, at least one voltage control, at least one boost, at least one capacitor and/or at least one bridge rectifier, persons of skill in the art being familiar with such components and being readily able to design appropriate circuitry to meet whatever current flow characteristics are desired. For example, circuitry that may be used in practicing the present inventive subject matter is described in: 
     U.S. patent application Ser. No. 11/626,483, filed Jan. 24, 2007 (now U.S. Patent Publication No. 2007/0171145), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/755,162, filed May 30, 2007 (now U.S. Patent Publication No. 2007/0279440), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 11/854,744, filed Sep. 13, 2007 (now U.S. Patent Publication No. 2008/0088248), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/117,280, filed May 8, 2008 (now U.S. Patent Publication No. 2008/0309255), the entirety of which is hereby incorporated by reference as if set forth in its entirety; 
     U.S. patent application Ser. No. 12/328,144, filed Dec. 4, 2008 (now U.S. Patent Publication No. 2009/0184666), the entirety of which is hereby incorporated by reference as if set forth in its entirety; and 
     U.S. patent application Ser. No. 12/328,115, filed on Dec. 4, 2008 (now U.S. Patent Publication No. 2009-0184662), the entirety of which is hereby incorporated by reference as if set forth in its entirety. 
     The lighting devices according to the present inventive subject matter can further comprise any suitable electrical connector, a wide variety of which are familiar to those of skill in the art, e.g., an Edison connector (for insertion in an Edison socket), a GU-24 connector, etc., or may be directly wired to an electrical branch circuit. 
     In some embodiments according to the present inventive subject matter, the lighting device is a self-ballasted device. For example, in some embodiments, the lighting device can be directly connected to AC current (e.g., by being plugged into a wall receptacle, by being screwed into an Edison socket, by being hard-wired into a branch circuit, etc.). Representative examples of self-ballasted devices are described in U.S. patent application Ser. No. 11/947,392, filed on Nov. 29, 2007 (now U.S. Patent Publication No. 2008/0130298), the entirety of which is hereby incorporated by reference as if set forth in its entirety. 
     Energy can be supplied to the at least one light source from any source or combination of sources, for example, the grid (e.g., line voltage), one or more batteries, one or more photovoltaic energy collection device (i.e., a device that includes one or more photovoltaic cells that convert energy from the sun into electrical energy), one or more windmills, etc. 
     Embodiments in accordance with the present inventive subject matter are described herein in detail in order to provide exact features of representative embodiments that are within the overall scope of the present inventive subject matter. The present inventive subject matter should not be understood to be limited to such detail. 
     Embodiments in accordance with the present inventive subject matter are also described with reference to cross-sectional (and/or plan view) illustrations that are schematic illustrations of idealized embodiments of the present inventive subject matter. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the present inventive subject matter should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a molded region illustrated or described as a rectangle will, typically, have rounded or curved features. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the present inventive subject matter. 
     The lighting devices illustrated herein are illustrated with reference to cross-sectional drawings. These cross sections may be rotated around a central axis to provide lighting devices that are circular in nature. Alternatively, the cross sections may be replicated to form sides of a polygon, such as a square, rectangle, pentagon, hexagon or the like, to provide a lighting device. Thus, in some embodiments, objects in a center of the cross-section may be surrounded, either completely or partially, by objects at the edges of the cross-section. 
       FIG. 1  is a cross-sectional view of a lighting device  10  according to the present inventive subject matter, and  FIG. 2  is a perspective view of the lighting device  10  of  FIG. 1 . 
     As seen in  FIG. 1 , the lighting device  10  also includes a light emitter board  14  mounted on the heat sink  12 . The light emitter board  14  includes a plurality of light sources  21 , which can be solid state light emitters, such as light emitting diodes (LEDs). The solid state light emitters can include light emitting diodes that emit blue light and light emitting diodes that emit red light, and the lighting device  10  can comprise luminescent material (e.g., as discussed below) that converts some of the blue light (i.e., light emitted by the light emitting diodes that emit blue light) into yellowish-green light or greenish yellow light, so that a mixture of light exiting the lighting device  10  is perceived as white light. 
     First and second major dimensions of the lighting device extend in a first plane (i.e., horizontally in the orientation shown in  FIG. 1  and perpendicular to the plane of the paper in  FIG. 1 ), and an emission plane for each of the light sources  21  is substantially parallel to the first plane. 
     The expression “emission plane of a light source,” (e.g., “an emission plane for each of the light sources”), as used herein, means (1) a plane that is perpendicular to an axis of the light emission from the light source(s) (e.g., in a case where light emission is hemispherical, the plane would be along the flat part of the hemisphere; in a case where light emission is conical, the plane would be perpendicular to the axis of the cone), (2) a plane that is perpendicular to a direction of maximum intensity of light emission from the light source(s) (e.g., in a case where the maximum light emission is vertical, the plane would be horizontal), (3) a plane that is perpendicular to a mean direction of light emission (in other words, if the maximum intensity is in a first direction, but an intensity in a second direction ten degrees to one side of the first direction is larger than an intensity in a third direction ten degrees to an opposite side of the first direction, the mean intensity would be moved somewhat toward the second direction as a result of the intensities in the second direction and the third direction). 
     In some embodiments, the light emitter board can be a metal core printed circuit board on which light sources, e.g., light emitting diodes are mounted. The light emitter board  14  can be thermally coupled to the heat sink  12  and may be thermally coupled to the heat sink  12  by direct contact, a thermal adhesive or other technique known to those of skill in the art. In some embodiments, the light emitter board  14  may be eliminated and the solid state light emitters may be mounted directly to the heat sink  12 . In such embodiments, i.e., where the solid state light emitters are mounted directly to the heat sink, the heat sink can be made such that it is adaptable to having the solid state light emitters mounted directly thereon using techniques used in making metal core printed circuit boards, e.g., by including a sheet of metal for providing an interconnection structure (e.g., three strings of light emitting diodes). 
     As is further illustrated in  FIG. 1 , the lighting device  10  also includes a light transmitting basket assembly  18 . The basket assembly  18  may include a frame and a cover element  11 . The cover element  11  may, for example, comprise an acrylic, polycarbonate, PET, PETG or other light transmissive material. 
     A representative example of a cover element  11  is depicted in  FIG. 3 . The cover element  11  shown in  FIG. 3  is in the shape of a lens. The cover element  11  comprises a light control element  13  which can include one or more regions that comprise volumetric light control structures (or the entire light control element can comprise a volumetric light control structure), and/or it can include one or more regions (on either or both major surfaces) that comprise surface light control features). With this cover  11 , each of the light sources  21  is spaced from the light control element  13  by substantially the same distance (i.e., the smallest distance from a point on the light source  21  to the nearest point on the light control element is substantially the same for each light source  21 ). The expression “substantially the same distance” when referring to first and second distances means that the first distance is between 0.90 to 1.10 times the second distance. 
     Another representative example of a cover element  11  is depicted in  FIG. 4 . The cover element  11  shown in  FIG. 4  comprises a light control element  13  in the form of a lens that contains a volumetric light control structure (alternatively or additionally, either or both major surfaces of the light control element  13  can contain one or more regions that comprise surface light control features) and a luminescent material  15  coated on the upper surface (in the orientation depicted in  FIG. 1 ) of the light control element  13 . Alternatively (or additionally), luminescent material  15  can be provided on the lower surface of the light control element  13  and/or dispersed within the light control element  13 , or it can be spaced from the light control element  13  and supported in any suitable way. 
     Another representative example of a cover element  11  is depicted in  FIG. 5 . The cover element  11  shown in  FIG. 5  comprises a light control element  13  and a lumiphor  17  (comprising luminescent material  15  dispersed within epoxy) on the upper surface of the light control element  11 . 
     Another representative example of a cover element  11  is depicted in  FIG. 6 . The cover element  11  shown in  FIG. 6  comprises a light control element  13  in the form of a film that contains a volumetric light control structure (alternatively or additionally, either or both major surfaces of the light control element  13  can contain one or more regions that comprise surface light control features) and a luminescent material  15  coated on the upper surface (in the orientation depicted in  FIG. 1 ) of the light control element  13 . Alternatively (or additionally), luminescent material  15  can be provided on the lower surface of the light control element  13  and/or dispersed within the light control element  13 , or it can be spaced from the light control element  13  and supported in any suitable way. The light control element  13  is positioned on a lens  19 . 
     Returning to  FIG. 1 , the basket assembly  18 , the upper housing  16  and the light emitter board  14  provide a mixing chamber in which light emitted from the LEDs is mixed by a combination of reflection within the chamber and the optical properties of the diffusing structures and/or films of the basket assembly  18 . Additionally, the interior surfaces of the mixing chamber may be covered in a reflective material, such as MCPET® from Furakawa Industries or any other reflective material, a wide variety of which are known by and available to persons skilled in the art (in some embodiments, particularly preferred reflective material is diffuse reflective material). Alternatively or additionally, any of the surfaces which light contacts can, in some embodiments, be coated with textured paint in order to alter brightness characteristics and/or patterns as desired. 
     Because many LEDs, such as Cree XRE LEDs, emit light in a substantially Lambertian distribution, the LEDs can be spaced from the sidewalls of the upper housing  16 . Thus, the light emitter board can have a surface area that is smaller than the area defined by the opening of the upper housing  16  through which light passes. Accordingly, the upper housing or a portion of the upper housing may be substantially frustopyramidal and have sloped or slanted sidewalls  16  to direct light from the light emitter board  14  toward the basket assembly  18 . Such slanted sidewalls may also help to direct light reflected from the basket assembly back toward the basket assembly so as to reduce light lost within the lighting device. 
     Additionally, because the light emitter board  14  may have a smaller area than the basket assembly  18 , the configuration of the basket assembly  18  and the upper housing  16  may be such as to spread the light from the LEDs across visible surfaces of the basket assembly  18  so as to avoid abrupt changes in luminance of the basket assembly  18  and the side reflector  20 . This may be accomplished, for example, with the mechanical configuration of the basket as described in U.S. patent application Ser. No. 12/116,341, filed May 7, 2008 (now U.S. Patent Publication No. 2008/0278952), the disclosure of which is incorporated herein as if set forth in its entirety, or by the optical properties of the lens(es) of the basket assembly as described below. 
     The side reflector  20  includes a flat lip portion  30  that can engage the grid of a suspended ceiling. Light exiting the lighting device  10  passes through a substantially square aperture defined by the lip portion  30  of the side reflector  20 . The side reflector  20  recesses the light generation portion of the lighting device  10  above the plane of the ceiling tile. 
     In one example of a representative embodiment, the outer perimeter of the rim measures about 2 feet by about 2 feet, and the outer perimeter of the basket assembly measures about 1 foot by about 1 foot. In the cases of embodiments where the opening in the supporting structure is not square, e.g., 2 feet by 4 feet, the devices according to the present inventive subject matter can be modified in any suitable way to provide the desired effect in the opening, e.g., to fill it, such as by using two devices (each measuring about 2 feet by 2 feet) side-by-side, or by providing a device in which the outer perimeter of the rim measures about 4 feet by about 2 feet. 
       FIG. 7  is a cross-sectional view of a lighting device  40  according to the present inventive subject matter, and  FIG. 8  is a bottom view of the lighting device  40  of  FIG. 7 . 
     Referring to  FIG. 7 , the lighting device  40  includes a light emitter board  41 , a plurality of light sources  42 , a side reflector  43 , a baffle assembly  44  and a plurality of cover elements  75 ,  76 ,  77 ,  78 ,  79 ,  105 ,  106 ,  107  and  108  (described below). 
     Referring to  FIG. 8 , the baffle assembly  44  comprises an outer baffle structure  71 , an intermediate baffle structure  72  and an inner baffle structure  73 . The outer baffle structure  71  includes four baffle elements  123 ,  124 ,  125 ,  126 . Similarly, intermediate baffle structure  72  includes four baffle elements  127 ,  128 ,  129 ,  130 , and the inner baffle structure  73  includes four baffle elements  131 ,  132 ,  133 ,  134 . The baffle assembly  44  further comprises connector portions  84 ,  85 ,  86 ,  87  extending from the outer baffle structure  71  to the first intermediate baffle structure  72 , and connector portions  88 ,  89 ,  90 ,  91  extending from the first intermediate baffle structure  72  to the inner baffle structure  73 . 
     Baffle structures (e.g., the outer baffle structure, the first intermediate baffle structure and the inner baffle structure) (if present), and/or side reflectors (if present) can be formed of any suitable material. Persons of skill in the art are familiar with a wide variety of suitable materials, including a variety of materials which are known for use in making baffles and/or side reflectors for light fixtures. A representative example of a suitable material for use in making the baffle structures and/or the side reflectors is MCPET®, marketed by Furukawa (a Japanese corporation). 
     The embodiment depicted in  FIGS. 7 and 8  includes a plurality of cover elements, namely, a first cover element  75  positioned between the baffle element  123  and the baffle element  127 . Similarly: 
     a second cover element  76  is positioned between the baffle element  125  and the baffle element  129 , 
     a third cover element  77  is positioned between the baffle element  127  and the baffle element  131 , 
     a fourth cover element  78  is positioned between the baffle element  129  and the baffle element  133 , 
     a fifth cover element  79  is positioned between the baffle element  131  and the baffle element  133 , and between the baffle element  132  and the baffle element  134 , 
     a sixth cover element  105  is positioned between the baffle element  126  and the baffle element  130 , 
     a seventh cover element  106  is positioned between the baffle element  124  and the baffle element  128 , 
     an eighth cover element  107  is positioned between the baffle element  130  and the baffle element  134 , and 
     a ninth cover element  108  is positioned between the baffle element  128  and the baffle element  132 . 
     Any of the cover elements  75 ,  76 ,  77 ,  78 ,  79 ,  105 ,  106 ,  107  and  108  can be a cover element as described herein, e.g., any of the cover elements  11  depicted in  FIG. 3 ,  FIG. 4 ,  FIG. 5  and  FIG. 6 . 
       FIG. 9  is a schematic diagram of a lighting device  150  according to the present inventive subject matter. The lighting device  150  includes a lower housing  151 , an upper housing  152 , a cover element  157  and light sources  163 . The lower housing  151  is a cast aluminum housing having fins surrounding the circumference and provides sidewalls of the mixing enclosure  158 . The lower housing may be a lower housing of an LR6 fixture from Cree LED Lighting Solutions, Inc., Durham, N.C., with the trim flange removed such that the housing does not extend past the cover element  157 . Other suitable lower housing materials having similar thermal properties could also be utilized. The lower housing  151  and the cover element  157 , in combination, comprise an enclosing structure that surrounds the light sources  163 . 
     The upper housing  152  includes a cavity  153  and also has fins to increase the overall area for heat extraction. The upper housing  152  has substantially the same configuration as the upper housing of the LR6 fixture. In the present embodiment, the upper housing  152  is made from copper. Other suitable upper housing materials having similar thermal properties could also be utilized. For example, the upper housing could be made from aluminum or other thermally conductive material. An electrically insulating layer  154  is provided within the upper housing  152  to isolate the power supply  165  from the upper housing  152 . The insulating layer  154  may, for example, be Formex. A thermal gasket (not shown) can be provided between the upper housing  152  and the lower housing  151  to assure a good thermal coupling between the two housings. The thermal gasket may, for example, be Sil-Pad from The Bergquist Company. 
     A top plate  155  is provided on the upper housing  152  and encloses the cavity  153 . A connector  156 , such as an Edison type screw connector, is provided on the top plate  155  to allow connection of the lighting device  150  to a power source, such as an AC line. Other connector types could be utilized and may depend on the power source to which the lighting device  150  is to be connected. 
     The cover element  157  is provided on the opening of the lower housing  151  to provide a mixing enclosure  158  having sidewalls defined by the lower housing  151  and opposing ends formed by the upper housing  152  and the cover element  157 . The cover element  157  can have a full width, half max (FWHM) of between 50° and 60°, which balances light transmission with diffusion to obscure the light sources. 
     The mixing enclosure  158  is lined with a highly reflective material  159 , such as MCPET® from Furakawa, to reduce losses from light reflected back into the mixing enclosure  158  by the cover element. The highly reflective material  159  reflects between 98% and 99% of the light across the visible spectrum. The lower (in the orientation depicted in  FIG. 7 ) end of the reflective material  159  defines a substantially circular aperture (through which substantially all of the light exiting the lighting device  150  exits. A reflective material  160  is also provided on a copper metal core circuit board  161  and may be provided on any exposed portions of the upper housing  152 . The reflective material  160  can also be MCPET®, laser cut to fit around the light sources  163 . 
     The light sources  163  are serially connected in a single string. This provides a high voltage string that allows for increased efficiency in driving the light sources  163 . 
     The power supply  165  is connected to the Edison connector  156  through wires  166  and  167 . 
     The cover element  157  can be a cover element as described herein, e.g., any of the cover elements  11  depicted in  FIG. 3 ,  FIG. 4 ,  FIG. 5  and  FIG. 6 . 
       FIGS. 10-11  illustrate a lighting device  50  in accordance with the present inventive subject matter.  FIG. 10  is a top view of the lighting device  50 .  FIG. 11  is a sectional view of the lighting device  50  taken along the plane  11 - 11 . 
     Referring to  FIGS. 10-11 , the lighting device  50  is a back-reflector, and comprises a cover element  51 , a rim  52 , a conductive trace  53 , a light source  54 , and a housing  55 . The surface of the housing  55  that faces the light source  54  is highly reflective. 
     The cover element  51  covers an aperture defined by the housing  55 . The cover element  51  can be a cover element as described herein, e.g., any of the cover elements  11  depicted in  FIG. 3 ,  FIG. 4 ,  FIG. 5  and  FIG. 6 . 
     The ability of the housing  55  to reflect light can be imparted in any suitable way, a variety of which are well known to persons of skill in the art. For example, the reflector(s) can comprise one or more material that is reflective (and/or specular, the term “reflective” being used herein to refer to reflective and optionally also specular), and/or that can be treated (e.g., polished) so as to be reflective, or can comprise one or more material that is non-reflective or only partially reflective and that is coated with, laminated to and/or otherwise attached to a reflective material. Persons of skill in the art are familiar with a variety of materials that are reflective, e.g., metals such as aluminum or silver, a dielectric stack of materials forming a Bragg Reflector, a dichroic reflector coating on glass (e.g., as described at www.lumascape.com/pdf/literature/C1087US.pdf), any other thin film reflectors, etc. Persons of skill in the art are familiar with a wide variety of materials which are suitable for making a non-reflective or partially reflective structure which can be coated with, laminated to or otherwise attached to a reflective material, including for instance plastic materials such as polyethylene, polypropylene, natural or synthetic rubbers, polycarbonate or polycarbonate copolymer, PAR (poly(4,4′-isopropylidenediphenylene terephthalate/isophthalate) copolymer), PEI (polyetherimide), and LCP (liquid crystal polymer). The reflector(s) can be formed out of highly reflective aluminum sheet with various coatings, including silver, from companies like Alanod (http://www.alanod.de/opencms/alanod/index.htm — 12063069299.html.), or the reflector(s) can be formed from glass. In cases where a lighting device according to the present inventive subject matter comprises more than one reflector, the respective reflectors can be made of the same material, or any reflector(s) can be made of different materials. 
     Representative examples of suitable reflectors (and arrangements thereof) are described in many patents, e.g., U.S. Pat. Nos. 6,945,672, 7,001,047, 7,131,760, 7,214,952 and 7,246,921 (the entireties of which are hereby incorporated by reference), each of which describes, among other things, back-reflectors. 
     While certain embodiments of the present inventive subject matter have been illustrated with reference to specific combinations of elements, various other combinations may also be provided without departing from the teachings of the present inventive subject matter. Thus, the present inventive subject matter should not be construed as being limited to the particular exemplary embodiments described herein and illustrated in the Figures, but may also encompass combinations of elements of the various illustrated embodiments. 
     Many alterations and modifications may be made by those having ordinary skill in the art, given the benefit of the present disclosure, without departing from the spirit and scope of the inventive subject matter. Therefore, it must be understood that the illustrated embodiments have been set forth only for the purposes of example, and that it should not be taken as limiting the inventive subject matter as defined by the following claims. The following claims are, therefore, to be read to include not only the combination of elements which are literally set forth but all equivalent elements for performing substantially the same function in substantially the same way to obtain substantially the same result. The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and also what incorporates the essential idea of the inventive subject matter. 
     Any two or more structural parts of the lighting devices described herein can be integrated. Any structural part of the lighting devices described herein can be provided in two or more parts (which may be held together in any known way, e.g., with adhesive, screws, bolts, rivets, staples, etc.).