Patent Publication Number: US-9839083-B2

Title: Solid state lighting apparatus and circuits including LED segments configured for targeted spectral power distribution and methods of operating the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 13/152,640; filed Jun. 3, 2011, entitled Systems and METHODS FOR CONTROLLING SOLID STATE LIGHTING DEVICES AND LIGHTING APPARATUS INCORPORATING SUCH SYSTEMS AND/OR METHODS, and claims priority to U.S. Provisional Patent Application No. 61/912,846; filed Dec. 6, 2013, entitled SOLID STATE LIGHTING APPARATUS AND CIRCUITS INCLUDING LED SEGMENTS CONFIGURED FOR TARGETED SPECTRAL POWER DISTRIBUTION AND METHODS OF OPERATING THE SAME, the disclosures of which are hereby incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to the field of lighting in general, and more particularly, to solid state lighting. 
     BACKGROUND 
     Solid state lighting arrays are used for a number of lighting applications. For example, solid state lighting panels including arrays of solid state light emitting devices have been used as direct illumination sources, for example, in architectural and/or accent lighting. A solid state light emitting device may include, for example, a packaged light emitting device including one or more light emitting diodes (LEDs), which may include inorganic LEDs, which may include semiconductor layers forming p-n junctions and/or organic LEDs (OLEDs), which may include organic light emission layers. 
     Visible light may include light having many different wavelengths. The apparent color of visible light can be illustrated with reference to a two dimensional chromaticity diagram, such as the 1931 International Conference on Illumination (CIE) Chromaticity Diagram illustrated in  FIG. 1 , and the 1976 CIE u′v′ Chromaticity Diagram shown in  FIG. 1B , which is similar to the 1931 Diagram but is modified such that similar distances on the 1976 u′v′ CIE Chromaticity Diagram represent similar perceived differences in color. These diagrams provide useful reference for defining colors as weighted sums of colors. 
     As shown in  FIG. 1 , colors on a 1931 CIE Chromaticity Diagram are defined by x and y coordinates (i.e., chromaticity coordinates, or color points) that fall within a generally U-shaped area. Colors on or near the outside of the area are saturated colors composed of light having a single wavelength, or a very small wavelength distribution. Colors on the interior of the area are unsaturated colors that are composed of a mixture of different wavelengths. White light, which can be a mixture of many different wavelengths, is generally found near the middle of the diagram, in the region labeled  100  in  FIG. 1 . There are many different hues of light that may be considered “white,” as evidenced by the size of the region  100 . For example, some “white” light, such as light generated by sodium vapor lighting devices, may appear yellowish in color, while other “white” light, such as light generated by some fluorescent lighting devices, may appear more bluish in color. 
     Light that generally appears green is plotted in the regions  101 ,  102  and  103  that are above the white region  100 , while light below the white region  100  generally appears pink, purple or magenta. For example, light plotted in regions  104  and  105  of  FIG. 1  generally appears magenta (i.e., red-purple or purplish red). 
     It is further known that a binary combination of light from two different light sources may appear to have a different color than either of the two constituent colors. The color of the combined light may depend on the relative intensities of the two light sources. For example, light emitted by a combination of a blue source and a red/orange source may appear purple or magenta to an observer. Similarly, light emitted by a combination of a blue source and a yellow source may appear white to an observer. 
     Also illustrated in  FIG. 1  is the Planckian locus  106 , which corresponds to the location of color points of light emitted by a black-body radiator that is heated to various temperatures. In particular,  FIG. 1  includes temperature listings along the Planckian locus. These temperature listings show the color path of light emitted by a black-body radiator that is heated to such temperatures. As a heated object becomes incandescent, it first glows reddish, then yellowish, then white, and finally bluish, as the wavelength associated with the peak radiation of the black-body radiator becomes progressively shorter with increased temperature. Illuminants which produce light which is on or near the Planckian locus can thus be described in terms of their correlated color temperature (CCT). 
     The chromaticity of a particular light source may be referred to as the “color point” of the source. For a white light source, the chromaticity may be referred to as the “white point” of the source. The white point of a white light source may fall along the Planckian locus. Accordingly, a white point may be identified by a correlated color temperature (CCT) of the light source. White light typically has a CCT of between about 2000 K and 10000 K. White light with a CCT of 3000 may appear yellowish in color, while light with a CCT of 8000 K may appear more bluish in color. Color coordinates that lie on or near the Planckian locus at a color temperature between about 2500 K and 8000 K may yield pleasing white light to a human observer. 
     “White” light also includes light that is near, but not directly on the Planckian locus. A Macadam ellipse can be used on a 1931 CIE Chromaticity Diagram to identify color points that are so closely related that they appear the same, or substantially similar, to a human observer. A Macadam ellipse is a closed region around a center point in a two-dimensional chromaticity space, such as the 1931 CIE Chromaticity Diagram, that encompasses all points that are visually indistinguishable from the center point. A seven-step Macadam ellipse captures points that are indistinguishable to an ordinary observer within seven standard deviations, a ten step Macadam ellipse captures points that are indistinguishable to an ordinary observer within ten standard deviations, and so on. Accordingly, light having a color point that is within about a ten step Macadam ellipse of a point on the Planckian locus may be considered to have a substantially similar color as the point on the Planckian locus. 
     The ability of a light source to accurately reproduce color in illuminated objects is typically characterized using the color rendering index (CRI). In particular, CRI is a relative measurement of how the color rendering properties of an illumination system compare to those of a reference illuminator, with a reference illuminator for a CCT of less than 5000K being a black-body radiator. For CCT of 5000K and above, the reference illuminator is a spectrum defined by the CIE which is similar to the spectrum of sunlight at the earth&#39;s surface. The CRI 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 illuminator. Daylight has the highest CRI (of 100), with incandescent bulbs being relatively close (about 95), and fluorescent lighting being less accurate (70-85). 
     Generally speaking, incandescent bulbs tend to produce more natural-appearing illumination than other types of conventional lighting devices. In particular, incandescent bulbs typically go from a color temperature of about 2700K at full brightness to a color temperature of about 2000 k at 5% brightness and to a color temperature of about 1800K at about 1% brightness. This compares favorably with daylight, which varies from about 6500K at midday to about 2500 k at sunrise and sunset. Research indicates that people tend to prefer warmer color temperatures at low brightness levels and in intimate settings. 
     In illumination applications, it is often desirable to provide a lighting source that generates a light with a color behavior that approximates the behavior of incandescent lighting. LED-lighting units have been proposed that may be coupled to an ac dimmer circuit (such as a rheostat or phase cut dimming circuit) and approximate the lighting variation of a conventional incandescent light as the dimmer circuit increases or decreases the brightness of the generated light, as described in U.S. Pat. No. 7,038,399 to Lys et al. 
     One difficulty with solid state lighting systems including multiple solid state devices, is that the manufacturing process for LEDs typically results in variations between individual LEDs. This variation is typically accounted for by binning, or grouping, the LEDs based on brightness, and/or color point, and selecting only LEDs having predetermined characteristics for inclusion in a solid state lighting system. LED lighting devices may utilize one bin of LEDs, or combine matched sets of LEDs from different bins, to achieve repeatable color points for the combined output of the LEDs. 
     One technique to tune the color point of a lighting fixture is described in commonly assigned United States Patent Publication No. 2009/0160363, the disclosure of which is incorporated herein by reference. The &#39;363 application describes a system in which phosphor converted LEDs and red/orange LEDs are combined to provide white light. The ratio of the various mixed colors of the LEDs is set at the time of manufacture by measuring the output of the light and then adjusting string currents to reach a desired color point. The current levels that achieve the desired color point are then fixed for the particular lighting device. LED lighting systems employing feedback to obtain a desired color point are described in U.S. Publication Nos. 2007/0115662 and 2007/0115228 and the disclosures of which are incorporated herein by reference. 
     It is known to provide a solid state lighting apparatus, such as one including Light Emitting Diodes (LEDs), that operates in response to a rectified ac voltage. In some conventional lighting devices, segments of the LED string can be separately biased so that as the magnitude of the rectified ac voltage increases, additional segments of the LED string can be forward biased so that light is provided in a sequentially increasing manner. Moreover, as the magnitude of the rectified ac voltage signal decreases (i.e. passes 90 degrees of phase) the separate LED segments are deactivated in reverse order. 
     SUMMARY 
     Embodiments according to the present invention can provide a solid-state lighting apparatus and circuits including LED segments configured for targeted spectral power distribution methods of operating the same. Pursuant to these embodiments, a dimmable solid state lighting apparatus can include a plurality of light emitting diode (LED) segments including a first LED segment that can have a targeted spectral power distribution for light emitted from the apparatus that is different than spectral power distributions for other LED segments included in the plurality of LED segments. An LED segment selection circuit can be configured to selectively control current through the plurality of LED segments to shift the light emitted by the apparatus to the targeted spectral power distribution responsive to dimming input. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a chromaticity diagram illustrating a Planckian locus using x and y chromaticity coordinates. 
         FIGS. 2A and 2B  illustrate a solid state lighting apparatus in some embodiments according to the invention. 
         FIG. 3  is a block diagram illustrating a solid-state lighting apparatus in some embodiments according to the invention. 
         FIG. 4  is a graphical and table representation of selective switching of LED segments of the apparatus shown in  FIG. 3  in some embodiments according to the invention. 
         FIG. 5  is a schematic diagram illustrating a solid-state lighting circuit in some embodiments according to the invention. 
         FIG. 6  is a schematic representation of an LED package including the LED segments illustrated in  FIG. 5  in some embodiments according to the invention. 
         FIG. 7  is schematic representation of a plurality of the LED packages shown in  FIG. 6  coupled together in a solid-state lighting apparatus in some embodiments according to the invention. 
         FIGS. 8A and 8B  are a perspective and a cross-sectional view of a solid-state lighting apparatus including the LED packages illustrated in  FIG. 7  in some embodiments according to the invention. 
         FIG. 9  is a graphical representation of instantaneous power in LED segments as a function of dimming phase angle in some embodiments according to the invention. 
         FIG. 10  is a block diagram illustrating a solid-state lighting apparatus in some embodiments according to the invention. 
         FIG. 11  is a block diagram illustrating a configuration of a solid-state lighting apparatus including particular CCT values in each of the LED segments in some embodiments according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS ACCORDING TO THE INVENTION 
     Embodiments of the present inventive subject matter are described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the present inventive subject matter are shown. This present inventive subject matter may, however, be embodied in many different forms and 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 present inventive subject matter to those skilled in the art. Like numbers refer to like elements throughout. 
     The expression “lighting apparatus”, as used herein, is not limited, except that it indicates that the device is capable of emitting light. That is, a lighting apparatus 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 following description of some embodiments of the inventive subject matter refers to “light emitting devices,” (LED) which may include, but is not limited to, solid-state lighting devices, such as light emitting diode devices. As used herein, “LED” includes, but is not limited to, direct-emission devices that produce light when a voltage is applied across a PN junction thereof, as well as combinations of such direct-emission devices with luminescent materials, such as phosphors that emit visible-light radiation when excited by a source of radiation, such as a direct-emission device. 
     In some embodiments, the present invention can be utilized in connection with bypass circuits, using the current sensed in the LED string and the temperature associated therewith, as described in co-pending and commonly assigned U.S. patent application Ser. No. 12/566,195 entitled “Solid State Lighting Apparatus with Controllable Bypass Circuits and Methods of Operating Thereof”, co-pending and commonly assigned U.S. patent application Ser. No. 12/704,730 entitled “Solid State Lighting Apparatus with Compensation Bypass Circuits and Methods of Operation Thereof” and co-pending and commonly assigned U.S. patent application Ser. No. 12/566,142 entitled “Solid State Lighting Apparatus with Configurable Shunts”, the disclosures of which are incorporated herein by reference. Temperature compensation is described in co-pending and commonly assigned U.S. patent application Ser. No. 13/565,166, (P1513), entitled “Temperature Curve Compensation Offset” the disclosure of which is incorporated herein by reference. 
     Referring to  FIGS. 2A and 2B , a lighting apparatus  10  according to some embodiments is illustrated. The lighting apparatus  10  shown in  FIGS. 2A and 2B  is a “recessed downlight” or “can” lighting fixture that may be suitable for use in general illumination applications as a down light or spot light. However, it will be appreciated that a lighting apparatus according to some embodiments may have a different form factor. For example, a lighting apparatus according to some embodiments can have the shape of a conventional light bulb, a pan or tray light, an automotive headlamp, or any other suitable form. 
     The lighting apparatus  10  generally includes a can shaped outer housing  12  in which a lighting panel  20  is arranged. In the embodiments illustrated in  FIGS. 2A and 2B , the lighting panel  20  has a generally circular shape so as to fit within an interior of the cylindrical housing  12 . Light is generated by solid state lighting devices (LEDs)  22 , which are mounted on the lighting panel  20 , and which are arranged to emit light  15  towards a diffusing lens  14  mounted at the end of the housing  12 . Diffused light  17  is emitted through the lens  14 . In some embodiments, the lens  14  may not diffuse the emitted light  15 , but may redirect and/or focus the emitted light  15  in a desired near-field or far-field pattern. The LEDs  22  may include LEDs of different chromaticities that may be selectively controlled to produce a desired intensity, correlated color temperature (CCT) and/or color rendering index (CRI) using various techniques discussed herein. 
     It will be understood that the term LED “segment” refers to a separately switched portion of an LED string. A segment can include at least one LED device, which can itself include a number of serially connected epi junctions used to provide a device that has a particular forward voltage, such as 3V, 6V, 9V, etc. where a single epi junction may have a forward voltage of about 1.5 volts. Each segment may include multiple LEDs that are connected in various parallel and/or serial arrangements. The segments LEDs may be configured in a number of different ways and may have various compensation circuits associated therewith, as discussed, for example, in commonly assigned co-pending U.S. application Ser. No. 13/235,103. U.S. application Ser. No. 13/235,127. 
     It will be understood that the term “targeted” can include configurations of the LED segments that are configured to provide a pre-defined lighting characteristic that is a specified parameter for the lighting apparatus. For example, a targeted spectral power distribution can be a spectral power distribution that is specified for the light provided by the apparatus as a result of dimming the light. In particular, the targeted spectral power distribution can describe the characteristic of the light that is generated at a particular dimming level. In some embodiments according to the invention, the targeted spectral power distribution can be specified on the packaging of the lighting apparatus or otherwise in conjunction with the advertising or marketing of the lighting apparatus. Furthermore, the targeted spectral power distribution can be associated with the lighting characteristics of two or more specified dimming levels, such as a low light level and a higher light level. Accordingly the targeted spectral power distribution can be provided as the light shifts from “full on” to more dimming as well a shift in the reverse direction toward “full on.” 
     Furthermore, an LED can be characterized as having a particular spectral power distribution, which can affect various light characteristics of the light emitted by the LED. It will be understood that a spectral power distribution can be used to express the power per unit area per unit wavelength of an illumination (radiant exitance), or more generally, the per wavelength contribution to any radiometric quantity (such as radiant energy, radiant flux, radiant intensity, radiance, irradiance, radiant exitance, and/or radiosity, etc.). It will be further understood that, a spectral power distribution may be normalized in some manner, such as, to unity at 555 or 560 nanometers, coinciding with the peak of the eye&#39;s luminosity function, in addition to the light characteristics described herein, such as CRI, CCT, CX and CY, etc. 
     The spectral power distribution of the combinations of LED segments can create an overall spectral power distribution for the lighting apparatus which can change based on which of the LED segments are on and for how long each of the LED segments is on. This timing associated with the LED segments having associated spectral power distributions can affect the lighting characteristics of the lighting apparatus including the Color Quality Scale (CQS), the dominant wavelength, the GAI, peak wavelength, the S/P ratio, the nonlinear brightness, the luminous efficacy, and the like. 
     It will be understood that Color Quality Scale (CQS) is a quantitative measure of the ability of a light source to reproduce colors of illuminated objects, which was developed by The National Institute of Standards and Technology (NIST). The characteristic of “dominant wavelength” (and complementary wavelength) are ways of describing non-spectral (polychromatic) light mixtures in terms of the spectral (monochromatic) light that evokes an identical perception of hue. For example, in  FIG. 1 , a straight line drawn between the point for a given color and the point for the color of the illuminant can be extrapolated so that it intersects the perimeter of the space in two points. The point of intersection nearer to the color in question can indicate the dominant wavelength of the color as the wavelength of the spectral color at that intersection point. The point of intersection on the opposite side of the color space gives the complementary wavelength, which when added to the color in question in the right proportion will yield the color of the illuminant. CQS is further described in, for example,  VISUAL EXPERIMENT ON LED LIGHTING QUALITY WITH COLOR QUALITY SCALE COLORED SAMPLES , N ICOLAS  P OUSSET , CIE 2010  Lighting Quality and Energy Efficiency,  14-17 Mar. 2010, which is incorporated herein by reference. 
     Gamut Area Index (GAI) refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a certain output device. GAI is further described in, for example, Color Rendering: A Tale of Two Metrics by Mark S. Rea et al., 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 192-202, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20399, which is incorporated herein by reference. 
     The ratio of scotopic luminance (or lumens) versus photopic luminance in a light source (S/P ratio) is a multiplier that can be used to determine the apparent visual brightness of a light source as well as how much light, that is useful to the human eye, a source emits. The luminous efficacy of a source is a measure of the efficiency with which the source provides visible light from electricity. Luminous efficacy is a measure of the proportion of the energy supplied to a lamp that is converted into light energy. It can be calculated by dividing the lamp&#39;s luminous flux, measured in lumens, by the power consumption, measured in watts. 
     As appreciated by the present inventors, an LED fixture can be configured as separately switched LED segments, each of which can have a respective spectral power distribution. Further, particular LED segments can be populated with LEDs of a particular spectral power distribution that is the target value for dimming. In operation, an LED segment selection circuit can selectively control the current through the particular LED segments so that the overall spectral power distribution of light generated by the apparatus shifts toward a targeted spectral power distribution as dimming proceeds. For example, a full spectral power distribution may be provided by the switching circuit to switch current through a combination of all of the LED segments. 
     It will be further understood, that in some embodiments according to the invention, the term “LED segment” can include any configuration of LEDs that allow for the LED segments to be separately controlled. For example, in some embodiments according to the invention, an LED segment can be a string of LEDs that can be controlled (such as by dimming) separately from one or more of the other LED segments included in the LED fixture. Accordingly, in such embodiments according to the invention, the LED segments can be arranged as separately controllable banks of LEDs, where each bank can be configured to have a particular spectral power distribution. It will be further understood that the LEDs within each of the “banks” can be configured in any way (including serial and parallel arrangements) which allows the respective bank to be controlled separately from the other banks. 
     For example, in some such embodiments including “banks” as the LED segments, a first bank can be populated with LEDs of a particular spectral power distribution that is the target value for dimming, such as a particular CCT value. Furthermore, the other banks of LEDs can include LEDs having respective different particular spectral power distributions. In operation, an LED segment selection circuit can selectively control the current through the LED segments so that the overall spectral power distribution of light generated by the apparatus shifts toward a targeted spectral power distribution as dimming proceeds. For example, a full spectral power distribution may be provided by the switching circuit to switch current through a combination of all of the LED segments. 
     In still other embodiments according to the invention, the LED segments can be configured in a serial string arrangement, where each LED segment may be controlled using, for example, the phase or level of a voltage signal that is used to drive the LED segment as a string. Accordingly, in such embodiments according to the invention, the LED segments can be arranged as separately controllable portions the LED string, where each LED segment of the string can be configured to have a particular spectral power distribution. For example, the LED segment having the lowest forward voltage of all of the LED segments can be populated with LEDs of a particular spectral power distribution that is the target value for dimming. In operation, an LED segment selection circuit can selectively switch the string current through the LED segments so that the overall spectral power distribution of light generated by the apparatus shifts toward a targeted spectral power distribution as dimming proceeds. For example, a full spectral power distribution may be provided by the switching circuit to switch current through a combination of all of the LED segments. 
     As dimming proceeds, however, the spectral power distribution of the light emitted by the apparatus can shift from the full spectral power distribution to a targeted spectral power distribution. Conversely, as dimming is reduced, the spectral power distribution of light output from the apparatus can shift from the targeted spectral power distribution back to the full spectral power distribution. In some embodiments according to the invention, the targeted spectral power distribution can be provided by the spectral power distribution of a particular LED segment (which may be provided by either a singular LED or a combination of LEDs in the particular segment), whereas the full spectral power distribution can be provided by the combination of the spectral power distribution all of the LED segments, and the time during which each is on. Accordingly, the targeted spectral power distribution can shift the generated light to appear more vivid, warmer, or to have a particular color (e.g., greenish) as the light is dimmed. 
     The targeted spectral power distribution, as well as the full spectral power distribution, can be provided by the combination of the light characteristics described herein associated with the LED segments provided. For example, in some embodiments according to the invention, different LED segments can have different values of ones of the lighting characteristics, such as CRI, such that when the apparatus is dimmed, the increasing portion of power provided to the targeted LED segment increases so that the targeted LED segment has a greater influence on the spectral power distribution of the apparatus due to the particular spectral power distribution of the targeted LED segment to which the increasing portion of power is delivered during dimming. 
     Furthermore, the shift in the spectral power distribution may, in some embodiments according to the invention, be irrespective of other lighting characteristics associated with the LED segments. For example, in the example described above, even though the different LED segments may have different CRI values, those LED segments may have identical CCT values. Accordingly, during dimming the apparatus may shift towards the targeted spectral power distribution associated with the targeted LED segment despite the fact that the CCT values for the segments are the same. Accordingly, spectral power distributions of the respective LED segments may be different based on at least one lighting characteristic of those LED segments being different from one another. 
     As further appreciated by the present inventors, an LED fixture can be configured as separately switched LED segments, each of which can have a respective CCT value. Further, the LED segment providing the targeted value can be populated with LEDs of a particular CCT value that is the target value for dimming. In operation, an LED segment selection circuit can selectively control the current through the LED segments so that the overall CCT value of light generated by the apparatus shifts toward a CCT target value as dimming proceeds. For example, at full brightness, a full CCT value may be provided by the fixture through a particular combination of all of the LED segments being on. As dimming proceeds, however, the CCT value of the light emitted by the apparatus can shift from the full CCT value to a targeted CCT value. Conversely, as dimming is reduced, the CCT light output from the apparatus can shift from the targeted CCT value back to the full CCT value. In some embodiments according to the invention, the targeted CCT value can be provided by the CCT value of a particular LED segment (which may be provided by either a singular LED or a combination of LEDs in the particular segment), whereas the full CCT value can be provided by a combination of the CCT values all of the LED segments, and the timing during which the segments are on. 
     As further appreciated by the present inventors, an LED string can be configured as separately switched LED segments, each of which can have a respective CCT value. Further, the LED segment having the lowest forward voltage of all of the LED segments can be populated with LEDs of a particular minimum CCT value that is the target value for dimming. For example, in some embodiments according to the invention, an LED string can include three separately switched segments: a high-voltage segment, a mid-voltage segment, and a low voltage segment, where the low voltage segment includes LEDs with a CCT value of the intended minimum CCT value to be provided as the target for dimming. 
     When dimming (such as phase cut dimming) is applied to such a these configuration, an increasing portion of the power over a cycle can be delivered to the low voltage segment including the minimum value CCT LEDs as dimming proceeds. Therefore, in some embodiments according to the invention, as the solid-state lighting apparatus is dimmed the emitted light may more closely approximate incandescent lighting when, for example, the minimum value CCT LEDs are “warm” in color such as that provided by LEDs having a CCT value of about 1800K or ccxy (0.55, 0.41). 
     In some embodiments of the invention, the LED segments in the string can be arranged according to the respective CCT values for the LED segments. In some embodiments according to the invention, the LED segments in the string can also be arranged according to their respective forward bias voltage. For example, in some embodiments according to the invention, the highest value CCT LEDs are included in the high-voltage segment, the minimum value CCT LEDs are included in the low-voltage segment, and the midrange value CCT LEDs are included in the mid-voltage segment. 
     In some embodiments according to the invention, the selective switching of the string current through the targeted LED segment, can be provided using magnitude interval bits that indicate the present magnitude of the rectified AC voltage signal. For example, in some embodiments according to the invention, an analog to digital conversion can be carried out on the rectified AC voltage signal to provide digital values indicative of the magnitude. The digital values can be used to control the states of switches used to selectively bypass the string current around the respective LED segment. As a cycle of the rectified AC voltage signal proceeds, the digital values provide an indication of the magnitude which is then used to select which LED segments should receive the string current and which should not. During dimming, the targeted LED segment can be selectively switched using a low order digital values representing the magnitude. Accordingly, as dimming proceeds, and increased portion of the power from the rectified AC voltage can be provided to the targeted LED segment, which generate light having the targeted spectral power distribution or targeted CCT value as described during. 
       FIG. 3  is a block diagram illustrating a solid-state lighting apparatus in some embodiments according to the invention. According to  FIG. 3 , an ac voltage signal is provided to a rectifier circuit  310  by a dimmer circuit  305 . It will be understood that the dimmer circuit  305  can provide the ac voltage signal in accordance with what is referred to as “phase cut dimming” where, for example, the level of the ac voltage signal remains clamped to zero up until a specified phase of the cycle. Beyond the specified phase, the ac voltage signal is not clamped to zero. For example, in some embodiments according to the invention, the dimmer circuit  305  may be configured to dim the light provided by the apparatus  300  by clamping the ac voltage signal to zero up until 90 degrees of phase within the ac voltage signal cycle, where after the rectified ac voltage signal is not clamped for the remainder of the phase. 
     It will be understood that the dimmer circuit  305  can be a leading edge phased cut dimmer circuit, a trailing edge phase cut dimmer circuit, or the like. In some embodiments according to the invention, the dimmer circuit  305  can be a rheostat circuit to reduce the magnitude of the ac input signal in response to dimming. In some embodiments according to the invention, the dimming can also be provide dimming control using a digital interface, such as those described on the Internet at http://www.lutron.com/TechnicalDocumentLibrary/Diva_0-10Vsubmittal.pdf, the entirety of which is hereby incorporated by reference. 
     The rectifier circuit  310  provides a rectified ac voltage signal  335  to a current source  320  to generate an LED string current  330 . It will be understood that the current source  320  can be a voltage controlled current source that is configured to regulate the string current  330  in response to the rectified ac voltage signal  335 . In some embodiments according to the invention, the rectified ac voltage signal  135  can have a frequency of about 120 Hz where, for example, the ac voltage signal provided to the rectifier circuit  310  has a frequency of about 60 Hz. It will be understood, however, that embodiments according to the invention can utilize ac voltage signals having any useable frequency. 
     The current source  320  is coupled to an LED string  325  that includes a plurality of separately switchable LED segments 1-N, electrically coupled in the series with one another. In some embodiments according at the invention, each of the separately switchable LED segments is configured to emit light having a particular CCT value. In some embodiments according to the invention, the LED segments can be arranged in the string  325  to include at least one targeted LED segment N which is configured to shift the characteristic of the light generated by the apparatus from any full targeted spectral power distribution to, for example, a targeted spectral power distribution, as dimming proceeds. In some embodiments according to the present invention, the targeted spectral power distribution can be provided using LEDs in the targeted segment that have particular CRI values, CCT values, efficacy values, S/P ratios or any other lighting characteristic that is intended to be specified as a target light for dimming. 
     In some embodiments according to the invention, the LED segments can be arranged in the string  325  to include at least one LED segment having a targeted CCT value targeted for dimming. For example, in some embodiments according to the invention, LED segment N is characterized as having a particular CCT value which is different from the other LED segments. Accordingly, as dimming proceeds, the light output from the apparatus  300  and shift in full CCT value provided by the combination of all LED segments toward a targeted CCT value represented by LED segment N. 
     In some embodiments according to the invention, the LED segments can be arranged in the string  325  in descending order according to the respective CCT values of the segments. For example, in some embodiments according to the invention, LED segment N is characterized as having the lowest CCT value of all of the segments, whereas LED segment is 1 characterized as having the highest CCT value of all of the segments. Still further, LED segment 2 is characterized as having a CCT value that is greater than that of segment N but less than that of segment 1. 
     Furthermore, the LED string  325  can be configured so that the LED segments are also arranged in descending order according to the respective forward bias voltages of the segments. For example, LED segment 1 can be configured with LEDs so that the forward bias voltage is about equal to 80 volts, whereas LED segment 2 can be configured with LEDs so that the forward bias voltage thereof it is about equal to 40 volts, and segment N can be configured with LEDs so that the forward bias voltage thereof is about equal to 20 Volts. 
     The rectified AC voltage signal  335  can also be provided to an LED segment selection circuit  315 , which can be configured to selectively switch current to particular ones of the LED segments based on the magnitude of the rectified ac voltage signal. In particular, the rectified AC voltage signal can be provided to an analog to digital converter (ADC)  340  which can generate magnitude interval bits used to provide control signals  345 ,  350 , and  355  to respective LED segment switches 1, 2, and N. It will be understood that the ADC  340  can be included in the LED segment selection circuit  315  or separately. It will be further understood that the indication of the magnitude interval can be provided using other techniques. 
     As further shown in  FIG. 3 , the LED segment switches 1-N are coupled across respective ones of the LED segments 1-N. In operation, the control signals  345 ,  350 , and  355  switch according to the magnitude interval timing to open/close the respective LED segment switch 1-N. When the particular control signal opens the respective LED segment switch, the string current  330  passes through the LED segment, where as when the control signal closes the respective LED segment switch, the string current bypasses the LED segment. Accordingly, the control signals  345 ,  350 , and  355  can be used to separately switch the string current  330  through/around each of the LED segments as the magnitude changes. 
     As further shown in  FIG. 3 , capacitors can be provided across each of the LED segments to address issues, such as, flicker. For example, when a particular LED segment switch opens, the string current  330  passes through the respective LED segment and charges the respective capacitor. In contrast, when the particular LED segments switch closes, the string current  330  passes through the LED segment switch to bypass the LED segment, but the capacitor can provide current to the LED segment that is bypassed by the string current  330 , to remain illuminated. Still further,  FIG. 3  also illustrates that blocking diodes can be included to prevent the capacitors from discharging (through the LED segment switch) when the LED segment switch closed. 
       FIG. 4  is a graphical and table representation of selective switching of LED segments of the apparatus shown in  FIG. 3  along with the magnitude of the rectified AC voltage signal in some embodiments according to the invention. According to  FIG. 4 , a portion of the rectified AC voltage signal  335  is annotated with indications of the magnitude interval bits across the horizontal axis. As shown, the magnitude interval bits transition from a first state (000) up to a last state (111) and then transition down again to the first state (000). Moreover, transitioning of many magnitude interval bits corresponds to the increase and decrease in the magnitude of the rectified AC voltage signal. Accordingly, the magnitude interval bits can be used as an indication of the magnitude of the rectified AC voltage signal so that the string current  332  can be selectively switched to the appropriate combination of LED segments during the different intervals of the rectified AC voltage signal cycle. 
     For example, assuming that the LED string  325  includes three LED segments having forward bias voltages of 80 V, 40 V, and 20 V, respectively, when the magnitude of the rectified AC voltage signal is about 20 V, the magnitude interval bits are (001) which can be used to switch the string current  330  through LED segment 3 but to bypass the remaining LED segments. When the magnitude of the rectified AC voltage signal reaches about 40 V, the magnitude interval bits are (010), which switches the string current through LED segment 2 but bypasses LED segments 1 and 3. 
     When the magnitude of the rectified AC voltage signal reaches about 60 volts, the magnitude interval bits are (011), which switches the string current  320  through LED segments 2 and 3 but bypasses LED segment 1. When the magnitude of the rectified AC voltage signal reaches about 80 V, the magnitude interval bits are (100), which switches the string current  320  through LED segment 1, but bypasses LED segments 2 and 3. When the magnitude of the rectified AC voltage signal reaches about 100 V, the magnitude interval bits are (101), which switches the string current  320  through LED segments 1 and 3, but bypasses LED segment 2. 
     When the magnitude of the rectified voltage signal reaches about 120 V, the magnitude interval bits are (110), which switches the string current  320  through LED segments 2 and 3, but bypasses LED segment 1. When the magnitude of the rectified voltage signal reaches about 140 V, the magnitude interval bits are (111), which switches the string current  320  through LED segments 1, 2, and 3. Operations continue, but in reverse order until the magnitude interval bits are (000) thereby completing the cycle of the rectified AC voltage signal. 
     When the circuit of  FIG. 3  is subject to dimming and operates according to  FIG. 4 , an increasing portion of the power provided over the cycle is delivered to the targeted LED segment including the LEDs having the targeted spectral power distribution configured by the particular lighting characteristics as described herein. As shown in  FIG. 9 , as the dimming phase angle decreases toward the low end of the range, an increasing portion of the power from the rectified AC voltage is provided to the low-voltage segment, which may be the targeted LED segment that provides the targeted spectral power distribution to which the light output shifts during dimming. 
     For example, in some embodiments according to the invention, the LED segments in the string can be configured such that non-targeted LED segments include relatively low CRI LEDs but with relatively high efficacy, whereas the targeted LED segment can include higher CRI LEDs but with relatively low efficacy. In response to dimming, the targeting spectral power distribution can be provided by the shift from relatively high lumen per watt output light with high efficacy to light that is relatively low efficacy but has higher CRI. Moreover, the shift toward the targeted spectral power distribution can be provided despite the fact that other lighting characteristics between the LED segments may be the same. For example, in some embodiments according to the invention, a targeted LED segment can include LEDs that are configured to generate light having a CRI of about 95 at low efficacy, whereas other LED segments can generate light having higher efficacy but at a CRI of about 75. 
     A particular light having a full spectral power distribution can be generated by the combination of all of the LED segments when the light is full on, for example. When the light is dimmed, however, an increasing portion of the power from the rectified ac voltage to the LED string is increasingly provided to the targeted LED segment so that the light generated shifts from the full spectral power distribution toward a targeted spectral power distribution that is pre-defined by the LEDs included in the targeted LED segment. Accordingly, the targeted spectral power distribution can have different lighting characteristics than the full spectral power distribution provided by the combination of all LED segments. 
     For example, in some embodiments according to the invention, where the targeted LED segment includes a minimum value CCT, as the solid-state lighting apparatus is dimmed the emitted light may more closely approximate incandescent lighting when, for example, the minimum value CCT LEDs are “warm” in color. For example, when phase cut dimming is applied at about 45° of phase (using leading edge or trailing edge dimming) to the circuit of  FIG. 3 , warm colored dimming may be more efficiently provided (i.e. without the use of additional components specifically intended for the provisioning of warm light dimming) as the segment with the minimum value CCT LEDs is more heavily utilized whereas the higher voltage LED segments are utilized less (due to the dimming). 
     It will be understood that the control of the separately switchable LED segments can be provided according to any method by which the timing or magnitude of the rectified ac voltage signal may be determined. For example, in some embodiments according to the invention, the switching may be provided using the techniques described in commonly assigned U.S. Pat. No. 8,476,836, the disclosure of which is incorporated herein by reference. 
       FIG. 5  is a schematic diagram illustrating a solid-state lighting apparatus in some embodiments according to the invention. In particular, the circuit shown in  FIG. 5  includes a rectification circuit  525  that provides the rectified AC voltage signal  335 , and a more detailed illustration of an exemplary voltage controlled current source  520  that can regulate the string current  330  in response to the magnitude of the rectified AC voltage signal  335  applied to the LED string  325 . In operation, the solid-state lighting apparatus shown in  FIG. 5  operates to selectively switch the string current through different ones of the LED segments responsive to the magnitude of the rectified AC voltage such that the LED segments switch on/off sequentially in response to the variation in the rectified AC voltage. 
     According to  FIG. 5 , the functionality of the LED segment selection circuit  315  shown in  FIG. 3  is provided by separate switching circuits  505 - 515 , coupled across a respective one of the LED segments shown in the string  325 . In operation, the switching circuits  505 - 515  provide the same functions described above with reference to  FIGS. 3 and 4  so that the appropriate LED segment is switched in/out of the string given the present magnitude of the rectified AC voltage signal. It will be understood at the switching circuits  505 - 515  maybe separately configured to indicate their respective connection (and voltage) to the particular LED segment in the string  325 . For example, the resistors shown connected to each of the switching circuits can be selected to indicate the position of the switching circuit in the LED string  325 , and the forward biasing needed for the particular LED segment across which the switch is coupled. 
     It will be understood that the switching circuits  505 - 515  can be provided by any circuit that allows the control described herein. For example, in some embodiments according to the invention, the switching circuits  505 - 515  can be provided by a 100 V MOSFET switch which operates as described. In such embodiments, the 100 V MOSFET switch can operate in an input voltage range of about 7.5 V to about 100 V, and may provide control of rise and fall times to provide low EMI. 
     Still further, the circuit illustrated in  FIG. 5  provides alternative configurations for the LED string. In particular, the LED string  325  includes three separately switchable LED segments configured for inclusion in the lighting apparatus operating from a 120 V AC power source. The uppermost LED segment provides a high voltage (80V) LED segment configured to have an associated CCT value of about 3100K. The middle LED segment provides a mid-voltage (40 V) LED segment configured to have an associated CCT value of about 2400K to about 2100K. The lowermost segment provides a low voltage (20 V) LED segment configured to have an associated CCT value of about 1800 K (i.e., the lowest CCT value among all of the LED segments in the string). 
     It will be understood that the LEDs included in each of the LED segments can be selected to provide a particular spectral power distribution for the respective segment in which those LEDs are included. In some embodiments according to the invention, LEDs included in the respective LED segment are configured to have a spectral power distribution that is equal to the target spectral power distribution for that segment. For example, a spectral power distribution of the targeted LED segment can be defined by a combination of the lighting characteristics described herein, such as CRI, CCT, etc. 
     The LED string  325   a , includes four separately switchable LED segments configured for inclusion in a lighting apparatus operating from 230 V AC power source. The upper LED segment provides a first high voltage (80V) LED segment configured to have an associated CCT value of about 3100K. In some embodiments according to the invention, The lower LED segment provides a low voltage (40 V) LED segment configured to have an associated CCT value of about 1800 K (i.e., the lowest CCT value among all of the CCT values for the LED segments in the string). 
     It will be understood that the LEDs included in each of the LED segments can be selected to provide a CCT value for the respective segment in which those LEDs are included. In some embodiments according to the invention, LEDs included in the respective LED segment are configured to have a CCT value that is equal to the target CCT value for that segment. For example, if the target CCT value for the lowest LED segment in  FIG. 5  is 1800 K., the LEDs included in that LED segment can each have a CCT value of 1800 K. 
       FIG. 10  is a block diagram illustrating a solid-state lighting apparatus in some embodiments according to the invention. According to  FIG. 10 , LED segments 1-N are provided in separately controllable respective LED segments arranged in banks. The LED segments 1-N can be separately controlled by an LED segment selection circuit  1015  using a LED segment control circuit  1040 . In some embodiments according to the invention, the LED segment control circuit  1040  can separately operate respective current sources  1020 - 1 -N for each of the LED segments responsive to input from the dimming circuit  305  to the LED segment selection circuit  1015 . For example, the current source  1020 - 1  can be used to control the current to LED segment 1, the current source  1020 - 2  can be used to control the current to LED segment 2, and the current source  1020 -N can be used to control the current to LED segment N. As further shown in  FIG. 10 , the current sources  1020 - 1 -N can draw current from a power source, such as a DC power source. Other power sources may also be used. 
     Each of the current sources  1020 - 1 -N can be set responsive to the input from the dimming circuit  305 . It will be understood that the dimming circuit  305  can be any circuit configured to communicate a level of dimming desired by a user or system. In some embodiments according to the invention, the dimming circuit  305  can also provide dimming control using a digital interface, such as those described on the Internet at http://www.lutron.com/TechnicalDocumentLibrary/Diva_0-10Vsubmittal.pdf, the entirety of which is hereby incorporated by reference. 
     In some embodiments according at the invention, each of the separately controlled LED segments 1-N is configured to emit light having a particular CCT value. In some embodiments according to the invention, the LED segments 1-N can be arranged to include at least one targeted LED segment N which is configured to shift the characteristic of the light generated by the apparatus from any full targeted spectral power distribution to, for example, a targeted spectral power distribution, as dimming proceeds. In some embodiments according to the present invention, the targeted spectral power distribution can be provided using LEDs in the targeted segment that have particular CRI values, CCT values, efficacy values, S/P ratios or any other lighting characteristic that is intended to be specified as a target light for dimming. 
     In some embodiments according to the invention, the LED segments 1-N can be arranged to include at least one LED segment having a targeted CCT value targeted for dimming. For example, in some embodiments according to the invention, LED segment N is characterized as having a particular CCT value which is different from the other LED segments. Accordingly, as dimming proceeds, the light output from the apparatus can shift from a full CCT value provided by the combination of all LED segments toward a targeted CCT value represented by LED segment N. 
       FIG. 11  is a block diagram illustrating a configuration of a solid-state lighting apparatus including particular CCT values in each of the LED segments in some embodiments according to the invention. According to  FIG. 11 , each of the LED segments 1-3 is characterized by a respective predetermined CCT value 1-CCT value 3, where LED segment 3 is the targeted segment for dimming. In some embodiments according to the invention, each of the CCT values corresponding to the particular LED segments can be located on Planckian locus in  FIG. 1 . Furthermore, it will be understood that the CCT values used herein include values that are within about seven Macadam ellipses of Planckian locus in  FIG. 1 . In some embodiments according to the invention, it will be understood that the CCT values used herein include values that are within about four Macadam ellipses of the Planckian locus in  FIG. 1 . Although three LED segments are shown in  FIG. 11 , it will be understood that any number of LED segments can be utilized in some embodiments according to the invention. 
     According to  FIG. 11 , in some embodiments according to the invention, LED segment 1 can be populated with LEDs such that the CCT value 1 for light emitted by the segment is equal to about 10000K to about 7,000K, LED segment 2 can be populated with LEDs such that the CCT value 2 for light emitted by the segment is equal to about 7000K to about 5000K, and LED segment 3 can be populated with LEDs such that the CCT value 3 for light emitted by the segment is equal to about 5000K to about 3000K. In some embodiments according to the invention, LED segment 1 can be populated with LEDs such that the CCT value 1 for light emitted by the segment is equal to about 7000K to about 5000K, LED segment 2 can be populated with LEDs such that the CCT value 2 for light emitted by the segment is equal to about 5000K to about 3000K, and LED segment 3 can be populated with LEDs such that the CCT value 3 for light emitted by the segment is equal to about 3000K to about 1000K. 
     In some embodiments according to the invention, as dimming proceeds, the LED segment selection circuit  1015  can separately control the LED segments 1-3 using current sources so that an increasing portion of the power is provided to the targeted LED segment (i.e. LED segment 3). It will be further understood, however, that in some embodiments according to the invention, any of the LED segments can be the targeted LED segment. For example, in some embodiments according to the invention, LED segment 1 or 2 can be LED segment that is targeted during dimming. 
       FIG. 6  is a schematic representation of an LED package including the LED segments illustrated in  FIG. 5  in some embodiments according to the invention. According to  FIG. 6 , a single LED package  940  is configured to include three segments which correspond to a segments described above in reference to, for example,  FIGS. 3-5 . The single LED package  940  can include a low-voltage LED segment  650  rated at about 22 V provided by coupling fourteen epi junctions in series with one another (where each at the junctions has a forward bias voltage of about 1.5 V). The single LED package  940  also includes a mid-voltage LED segment  670  rated at about 44 V provided by coupling two sets of fourteen epi-junctions in series with one another (where each at the junctions has a forward bias voltage of about 1.5 V). The single LED package  940  also includes a high-voltage LED segment  660  rated at about 88 V provided by coupling four sets of fourteen epi-junctions in series with one another (where each at the junctions has a forward bias voltage of about 1.5 V). The single LED package  940  also includes electrical i/o terminals for each of the LED segments. 
       FIG. 7  is schematic representation of a plurality of the LED packages shown in  FIG. 6  coupled in series together in a solid-state lighting apparatus in some embodiments according to the invention. In particular, each of the low-voltage segments  650  in the respective single LED packages  940  can be coupled together in series in the arrangement shown in  FIG. 7 . Similarly, each of the mid-voltage segments  670  and high-voltage segments  660  can be coupled together in series. 
       FIGS. 8A and 8B  are a perspective and a cross-sectional view of a solid-state lighting apparatus including the LED packages illustrated in  FIG. 7  in some embodiments according to the invention. According to  FIG. 8 , a housing  905  is coupled to an electrical connector  900  that is configured to releasably coupled to a standardized electrical fixture, which may be, for example, an Edison style or any other type of standardized electrical fixture. 
     A post  915  protrudes from the housing  905  and includes an outer surface that faces radially outward in a direction  920 . The plurality of the LED packages  950  is electrically coupled in series with one another, and is spaced apart on the outer surface around a circumference thereof. The illustrated arrangement may provide for improved incandescent style dimming by arranging the LED packages according to the present invention around the circumference if, for example, one or more one of the LED packages (entirely or partially) fails. 
     As described herein, an LED string can be configured as separately switched LED segments, each of which can have a different CCT value. Further, the LED segment having the lowest forward voltage of all of the LED segments can be populated with LEDs of a particular CCT value that is the target value for dimming. For example, in some embodiments according to the invention, an LED string can include three separately switched segments: high-voltage segment, a mid-voltage segment, and a low voltage segment, where the low voltage segment includes LEDs with a CCT value that is equal to the intended minimum CCT value to be provided during dimming. 
     When dimming (such as phase cut dimming) is applied to such a configuration, more of the instantaneous power provided over a cycle is delivered to the low voltage segment including the minimum value CCT LEDs. Therefore, in some embodiments according to the invention, as the solid-state lighting apparatus is dimmed the emitted light may more closely approximate incandescent lighting when, for example, the minimum value CCT LEDs are “warm” in color such as that provided by LEDs having a CCT value of about 1800K or ccxy (0.55, 0.41). 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present inventive subject matter. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element is referred to 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 as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     It will be understood that when an element is referred to as being “on” another element, the element can be directly on another element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Spatially relative terms, such as “below”, “beneath”, “lower”, “above”, “upper”, and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the Figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the Figures. 
     Embodiments of the inventive subject matter are described herein with reference to plan and perspective illustrations that are schematic illustrations of idealized embodiments of the 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, the inventive subject matter should not be construed as limited to the particular shapes of objects illustrated herein, but should include deviations in shapes that result, for example, from manufacturing. Thus, the objects illustrated in the Figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the inventive subject matter. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present 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” “comprising,” “includes” and/or “including” when used herein, 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. 
     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 present inventive subject matter belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. The term “plurality” is used herein to refer to two or more of the referenced item. 
     It will be understood that, as used herein, the term light emitting diode may include a light emitting diode, laser diode and/or other semiconductor device which includes one or more semiconductor layers, which may include silicon, silicon carbide, gallium nitride and/or other semiconductor materials, a substrate which may include sapphire, silicon, silicon carbide and/or other microelectronic substrates, and one or more contact layers which may include metal and/or other conductive layers. 
     In the drawings and specification, there have been disclosed typical preferred embodiments of the inventive subject matter and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the inventive subject matter being set forth in the following claims.