Patent Publication Number: US-9897304-B2

Title: LED light re-direction accessory

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 15/215,964 titled “LED Lighting,” filed by Frank Shum on Jul. 21, 2016, which is a Continuation-in-Part of U.S. patent application Ser. No. 14/952,079 titled “LED Lighting,” filed by Frank Shum on Nov. 25, 2015, which claims the benefit of U.S. Provisional Application Ser. No. 62/141,010 titled “LED Lighting,” filed by Frank Shum on Mar. 31, 2015. 
     This application incorporates the entire contents of the foregoing applications herein by reference. 
    
    
     TECHNICAL FIELD 
     Various embodiments relate generally to improved LED (light emitting diode) lighting sources, and some embodiments relate particularly to lightweight improved thermal management. Other embodiments relate to optics with optional accessories with tailored distributions targeted for particular optical distributions. Other Embodiments relate to electronics necessary for operation of the LED system with legacy ballast. 
     BACKGROUND 
     The field of LED lighting has made tremendous progress, however thermal management remains a challenge, in particular where the high light output is required relative to the allowable size of LED lighting system. This is a particular issue, namely, to replace high light output and high light density lamps and fixture. One such area that remains a challenge is high intensity discharge (HID) Lamps that have very high light output. For example, a 400 W HID lamp of less than 300 mm long and 120 mm diameter will have more than 35,000 lumens. 
     Types of HID lamps include metal halide lamp, high pressure sodium lamp and low pressure sodium lamps. These types of lamps require a warm up period of 1 to 15 minutes to reach 90% of their full light output. After a lamp has been operating for a period of time and then extinguished, it cannot be immediately turned back on. Before the lamp can be turned back on, the arc tube must have a chance to cool down or the lamp will not restart. This period of time is called the restrike time. Restrike times for traditional probe-start MH lamps can take 15 minutes or longer while restrike times for pulse-start MH lamps are generally much shorter. The long warm up time and long restrike time are a disadvantage. HID lamps may also contain mercury, a hazardous material, and may have only moderate life spans of about 10,000-20,000 hours, some may have rapid lumen depreciation in the first 3000-5000 hours. 
     In addition, HID lamps are an omni-directional light source which may be difficult to efficiently redirect into a more useful and efficient distribution. The optics used for redirecting the light can be expensive and lossy. For example, a fixture light loss factor, or the optical loss may typically be around 30%. So the moderate efficiency of a HID lamp is immediately discounted by 30%. It is also typically difficult to control the light, resulting glare that is not only wasted but a source of visual discomfort. 
     SUMMARY 
     Apparatus and methods relate to a lighting system having a unique combination of one or more of the following sub systems including: a light emitting diode (LED), a heatsink, an electronic driver, a primary optic that redirects at least a portion of the raw LED light distribution into a primary optical distribution, a secondary optical accessory that redirects at least a portion of the primary optical distribution into a secondary optical distribution, and an electronic accessory. The system may be an optical system such as, for example, a lamp, a fixture, a luminaire, a module, an optical sub system or a light engine. The sub systems, may be novel alone or in combination with other sub systems. The sub systems, or a combination thereof, may be novel and need not be related to LEDs. 
     In various embodiments, a set of combined geometries may provide for improved air flow to a heatsink, thus improving thermal dissipation. In some embodiments, the heat sink construction may allow for reduced weight. 
     In various embodiments, optics may be used to tailor the light into predetermined optical distributions, thus increasing the efficiency of the system. In a some embodiments, the distribution may be tailored to have a cut off such that above certain angles, there is substantially little light. In various embodiments, a secondary optical accessory may be used to change the optical distribution, for example, to provide uplight or asymmetrical distributions. 
     In some embodiments, the LED system may be designed to be less than 4 lbs with the capacity to emit greater than 10,000 lumens. In some embodiments, the LED systems may be designed to operate from offline AC voltage sources. In various embodiments, the LED systems may be designed to operate from a ballast. In some embodiments, the LED systems may be designed to operate from offline AC voltage sources. In various embodiments, the LED systems may be designed to operate from a ballast and from offline AC voltage sources. 
     Although the technology described is particularly applicable to LED lamps such as PAR, MR, BR, HID shapes, it can also be applied to build LED fixtures or more generally any LED systems. In some embodiments, the LED lighting system may replace HID lamps used in high bay or low bay applications. In some implementations, references to high bay also apply to low bay implementations and vice versa. 
     In the illustrations and embodiments of this disclosure, the orientation of LED system is shown with LED pointing in a downward orientation so the air flow from bottom through the LED and/or optics into interior of the heatsink and outward through the back of the LED system. However, the orientation may be reversed so the inlet is the back of the LED system and the air outlet is the front of the system. In other embodiments, the LED system may be of a skewed orientation. As such, the embodiments are not necessarily restricted to any particular orientation. 
     The details of various embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  depicts an isometric view of an exemplary LED system. 
         FIG. 1B  depicts an exploded view of an exemplary LED system. 
         FIG. 2A  depicts a front view an exemplary LED embodiment. 
         FIG. 2B  depicts a conceptual view of exemplary opening or open regions between the LEDs. 
         FIG. 2C  depicts a conceptual view of exemplary openings of a LED. 
         FIG. 3  depicts a rear view of a primary optic having at least one optic. 
         FIG. 4A  depicts a raw light output distribution from an exemplary LED 
         FIG. 4B  depicts a reflector with a reflective surface redirecting at least a portion of a raw light output from an exemplary LED package. 
         FIG. 4C  depicts a light output distribution of a total internal reflection (TIR) lens. 
         FIG. 4D  depicts a light output distribution of a dielectric CPC. 
         FIG. 4E  depicts a light output distribution of a dielectric CPC with an output surface explicitly curved in a convex shape. 
         FIG. 4F  depicts a side view of an LED system having multiple LED packages  420  corresponding to one optic. 
         FIG. 5A  depicts a top view of an exemplary primary optic. 
         FIG. 5B  depicts a conceptual view of exemplary opening having at least three optics that form an outer perimeter. 
         FIG. 5C  depicts a conceptual view of an exemplary opening within an outer perimeter. 
         FIG. 6A  depicts a polar plot illustrating an exemplary optical intensity for a Lambertian optical intensity distribution of a raw light output from an LED. 
         FIG. 6B  depicts a plotted Cartesian light distribution where an x-axis is plotted from 0-90°. 
         FIGS. 6C, 6D, 6E, and 6F  illustrate characteristics of various different optical distributions. 
         FIG. 7A  depicts a cross section view of an exemplary LED system having a heatsink. 
         FIG. 7B  depicts a front view of an exemplary LED system having the optic removed for to reveal the LED locations. 
         FIGS. 8A, 8B, 8C, 8D, 8E, and 8F  depict various views of an exemplary LED system having a heatsink with elongated features. 
         FIGS. 9A-9B  depict various views of an exemplary LED system 
         FIGS. 10A-10B  depict an isometric view and a front view of an exemplary heat sink having at least two fins. 
         FIGS. 10C-10D  depict an isometric view and a front view of an exemplary heatsink having fins of different radial lengths. 
         FIGS. 10E-10F  depict an isometric view and a front view of an exemplary heatsink having an opening in the center. 
         FIGS. 11A-11B  depict an isometric view and a front view of an exemplary heatsink. 
         FIG. 11C  depicts an exploded view of an exemplary heatsink. 
         FIGS. 11D and 11E  depict an exemplary set of a pair of fins. 
         FIGS. 12A, 12B and 12C  depict an isometric view and a front view of an exemplary optical accessory. 
         FIG. 13A  depicts the front view of an exemplary optical system  101  having an optical accessory. 
         FIG. 13B  depicts a cross section view of an exemplary optical system having an optical accessory. 
         FIG. 13C  depicts an illustrative ray trace of a cross section of an exemplary optical system. 
         FIG. 14  depicts perspective view of an optical accessory. 
         FIG. 15  depicts a top perspective view of an exemplary optical accessory having an additional optical accessory region  1501  that is used to redirect the light from the interior of corresponding LEDs. 
         FIG. 16A  depicts a schematic of an exemplary 400 W Probe Start Metal Halide ballast designed to work with a probe start M59 Metal Halide lamp load. 
         FIG. 16B  depicts a schematic of a 400 W Pulse Start Metal Halide ballast designed to work with probe start M135 Metal Halide lamp load. 
         FIG. 17  depicts a schematic of an exemplary electronic LED driver designed to interface with a magnetic ballast. 
         FIG. 18  depicts a schematic of an electronic LED driver designed to interface with a magnetic ballast having a bridge, a switch controlled by a controller unit, a smoothing capacitor and a string of LEDs with total forward voltage V f . 
         FIG. 19  depicts possible methods by which a controller unit controls a switch. 
         FIGS. 20A, 20B, 20C, 20D, 20E, 20F, 20G, and 20H  depict various schematic of an exemplary single LED driver specifically designed to be able to be power by either a magnetic ballast or directly with the offline AC source V s . 
         FIGS. 21A, 21B, 21C, 21D, and 21E  depict various schematics of an exemplary electronic LED driver designed to be powered by a ballast or to be powered directly with the offline AC source. 
         FIG. 22  depicts a schematic of an exemplary electronic LED driver using a fly back topology designed to be powered by a ballast or to be powered directly with the offline AC source. 
         FIG. 23  depicts possible methods by which a controller unit controls a switch with at least two frequency components. 
         FIGS. 24A and 24B  depict control scheme schematics that allow for improved power factor and harmonic distortion. 
         FIG. 25  depicts a process by which the control scheme can determine the type of power source it is connected to. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     ILLUSTRATIVE EMBODIMENTS 
       FIG. 1A  depicts an isometric view of an exemplary LED system. As depicted, the LED system is in the form factor of a LED Lamp  100 . 
       FIG. 1B  depicts an exploded view of an exemplary LED system. With reference to  FIG. 1A , the LED system includes the following subsystems: a light emitting diode (LED)  101 , a heatsink  102 , an electronic driver  106 , a primary optic  103 , a secondary optic accessory  104 , and an electronic accessory  105 . 
     Each sub system  101 - 106 , having characteristics, features, permutations or variations described in further detail below. 
     LED 
     The LED referenced in this disclosure is intended to be very general in nature. The LED includes at least one light emitting semiconductor die and, optionally, packaged with phosphor or integral optic or external optic or mounted on to a PCB. 
     The LED having at least a portion of its spectrum emitting in the range 250 nm to 900 nm, such as, for example, UV, visible or infrared regions. 
     The LED may be packaged in a format that allows for mounting to a PCB. The PCB material, such as, for example, fiber glass resin material (e.g., FR4) or a metal core printed circuit board (MCPCB), may have improved thermal dissipation characteristics. The LED package may be a surface mountable device (SMD), chip on board (COB) or chip scale package (CSP) or other well know packaging methods. 
     In the event where there are at least two LEDs, the LEDs may have substantially similar spectrums or substantially dissimilar spectrums. For example, different spectrums may include a color that is red, orange, yellow, green, blue, indigo, violet, ultra violet or infra-red or different color temperatures of white. 
       FIG. 2A  depicts a front view an exemplary LED embodiment. With reference to  FIG. 1B , LED  101  includes one hundred and forty-four LED packages  201  mounted to a printed circuit board (PCB)  202 . The LEDs are arranged in an inner ring or perimeter  221 , a middle ring or perimeter  222  and an outer ring or outer perimeter  223 . The middle perimeter  222  does not cross the outer perimeter  223 . The inner most perimeter  221  does not cross the middle perimeter  222 . The word ring and perimeter are used interchangeably. As depicted, the outer ring has more LEDs than the inner ring. The inner ring  221  having twenty-four LED packages, the middle ring  222  having forty-eight LED packages, and the outer ring  223  having seventy-two LED packages. The outer ring  223  encircling, encompassing, enclosing or containing all the LEDs as well as the middle ring  222  and inner most ring  221 . The middle ring  222  containing the inner ring  221 . At least one open region  205   a  is contained between the middle ring  222  and the outer ring  223 . At least one open region  205   b  is contained between the inner ring  221  and the middle ring  222 . At least one open region  205   c  is contained within the inner ring  221 . The open regions  205   a ,  205   b  and  205   c  may allow for air flow. 
     Spreading the LEDs across multiple rings may provide advantages over a single ring containing all the LEDs or if all the LEDs were concentrated in a central region. The placing of LEDs across multiple rings may enable the LED to be thermally distributed more evenly across the surface contained within the outer perimeter and thereby lower thermal while enabling more LEDs to be disposed on the surface. In various embodiments, the LED may include at least one opening between the rings of LEDs. 
       FIG. 2B  depicts a conceptual view of exemplary opening or open regions between the LEDs. As depicted, a LED (e.g., the LED  101 ) includes at least 3 LEDs  207 - 209 , each LED  207 - 209  mounted on a printed circuit board (PCB)  211 - 213 , respectively. The PCBs  211 - 213  may be mechanically isolated or mechanically connect to each other. For example, the dotted lines may represent PCB, or other material, that mechanically connects to at least two of the PCB  211 - 213 . An outer perimeter  216  is formed by the outer LEDs  207 - 209 . The outer perimeter  216  containing, encompassing, encircling, or containing all the LEDs in the system. The PCB open region  221  is formed within the outer perimeter  216  and between the PCBs  211 - 213  allowing for air to flow between the LEDs. 
       FIG. 2C  depicts a conceptual view of exemplary openings or open regions between the LEDs. With reference to  FIG. 2B , the LED further includes an inner perimeter  226  contained within the outer perimeter  216 . As depicted, the inner perimeter is formed by three LEDs  227 - 229 . Each LED  227 - 229  mounts on a PCB  231 - 233 , respectively. At least one of the LEDs  227 - 229  forming the inner perimeter  226  may be different than the LEDs  207 - 209  forming the outer perimeter  216 . The outer perimeter  216  and the inner perimeter  226  do not cross each other. The outer perimeter  216  encloses the inner perimeter  226 . The PCBs  227 - 229  may be mechanically isolated or mechanically connect together. For example, the dotted lines may represent PCB, or other material, that mechanically connects at least two of the PCBs  227 - 229 . The inner perimeter  226  contains at least one inner open region  225  that allows for air flow between the LEDs. The inner perimeter  226  is completely contained by the outer perimeter  216 . The addition of the inner perimeters  226 , with optics (not shown), allows for the LEDs, and thus the LED generated heat, to be optimally spread across a surface defined and bounded by the outer perimeter, allowing for improved heat dissipation resulting and a more even temperature distribution across the heatsink surface. 
     In various embodiments, at least one of the LEDs  227 - 229  may be mounted near the edge or near the perimeter of the mechanics that comprise the LED optical system. In some embodiments, the LEDs  227 - 229  may be mounted within 25 mm of the edge of the optical system. With reference to  FIGS. 1B-2B , the outer ring of the LED  223  is mounted within 25 mm of the diameter edge of the heatsink  102 . 
     Primary Optic 
     The primary optic redirects at least a portion of light from at least one LED into a first optical distribution. The type of optic is intended to be very general and may accomplish the redirection of light through mechanisms such as reflection or refraction or combinations thereof. Reflective or refractive elements may include convex lens, concave lens, air compound parabolic reflector (air CPC), dielectric compound parabolic reflector (dielectric CPC), Fresnel lens, total internal reflection lens (TIR), gradient index lens, diffractive lens, micro lenses, micro structures, diffractive optics, segmented lens, RXI lens, light guide or light guide taper or combinations thereof. The primary optic may consist of a single optic or an array of optics. 
     In some embodiments, the LED system may include at least three LEDs, each LED having its own optic. Within an outer perimeter formed by the at least three LEDs, at least one open region may be formed within the optic and LEDs that allows for improved air flow when compared to an open region that is blocked. 
     In some embodiments, the LED system  101  has at least three LED packages and at least one optic. The optic may be shared by the LEDs. The optic may have an open region. An outer perimeter formed by the at least three LEDs includes at least one open region. The open region for the optic and the LEDs may allow for improved air flow. In an illustrative example, the optic may be a reflector, such as, for example, a prismatic reflector, a mirror, or an aluminum metal reflector. Such reflector structures may have an open structure that allows for air flow. 
       FIG. 3  depicts a rear view of primary optic having at least one optic  301 . With reference to  FIGS. 1A-3 , each optic  301  corresponds to at least one LED package  201  of the LED  101 . The optic  301  redirects at least a portion of the raw light output, from at least one LED package  201 , into a first optical distribution. As depicted, there are one hundred and forty-four optics  301 . The optics  301  are arranged such that an inner ring  321  of twenty-four optics corresponds to the LED packages  201  of the inner ring  221 , a middle ring  322  of forty-eight optics corresponds to the LED packages  201  of the middle ring  222 , and an outer ring  323  of seventy-two optics corresponds to the LED packages  201  of the outer ring  223 . The individual optics  301  are held together by a holder  302  to form a common mechanical unit held together for ease of assembly. The material for the optics may be substantially optically transmissive and include material such as acrylic, polycarbonate or glass. If the material is plastic, the material may be fabricated using injection molding or compression molding techniques. 
       FIG. 4A  depicts a raw light output distribution from an exemplary LED. As depicted, a raw light output  402  from an exemplary LED package  401  tends to be substantially Lambertian in distribution with a full width half maximum beam angle (FWHM) of about 120 degrees (120°). The purpose of the primary optic is redirect at least a portion of this raw output into an overall first optical distribution. In some embodiments, the first optical distribution has a FWHM&lt;120°, for example FWHM&lt;100° or FWHM&lt;90°. 
       FIG. 4B  depicts a reflector with a reflective surface redirecting at least a portion of a raw light output from an exemplary LED package. The total resulting light includes redirected and un-redirected light which form a first optical distribution  403 . A reflective surface  404  may be formed by a metal coating on to a substrate material of appropriate shape to reflect the incident light into at least a portion of the first optical distribution. In such a case, since the light does not penetrate the substrate material, the substrate material needs not be optically transmissive. In some embodiments, at least a portion of the reflective surface  404  may be substantially in the shape, or based on the shape, of a compound parabolic concentrator (CPC). 
       FIG. 4C  depicts a light output distribution of a total internal reflection (TIR) lens. Input refractive surfaces  406 ,  407  refract at least a portion of the raw light output  402  from the LED  401 . At least a portion of the light refracted by input surface  407  is further refracted by exit surface  409 . At least a portion light refracted by input surface  406  is reflected by TIR surface  408  and then refracted by exit surface  409 . The total resulting light forms a first optical distribution  410 . 
       FIG. 4D  depicts a light output distribution of a dielectric CPC. An input surface  412  refracts at least a portion of the raw light output  402  from the LED  401 . At least a portion of the light refracted by the input surface  412  is further refracted by an exit surface  414 . At least a portion of the light refracted by the input surface  412  is further totally internally reflected by a surface  413  and then refracted by an exit surface  414 . The total resulting light forms a first optical distribution  415 . In an illustrative example, the surfaces  414 ,  412  are substantially flat. In some embodiments, at least a portion of either of the surfaces  414 ,  412  are curved. 
       FIG. 4E  depicts a light output distribution of a dielectric CPC with an output or exit surface explicitly curved in a convex shape. As depicted, a first optical distribution  417  results from an output surface  416  being explicitly curved in a convex shape. The output surface  416  may advantageously reduce wide angle rays in the first optical distribution  415  to a distribution  417  with less wide angle light. The resulting distribution  417  may reduce glare. 
       FIG. 4F  depicts a side view of an LED system having multiple LED packages corresponding to one optic. As depicted, an optic  421  is shared by at least three of the LEDs  420  (third LED not shown). The optic  421  having an open region  422 . Within an outer perimeter, formed by at least three LEDs  420 , includes an open region  425 . In various embodiments, the outer perimeter may include multiple open regions. The open region  425 , as formed by the optic  421  and the LEDs  420  may allow for improved air flow  423 ,  424 . For example, the optic  421  may be a reflector, such as, for example, a prismatic reflector, or a coated mirror, or an aluminum metal reflector. Generally, such reflectors are open structures to permit air to flow freely. 
       FIG. 5A  depicts a bottom view of an exemplary primary optic. With reference to  FIGS. 1 and 3 , the LED system  101  includes an outer perimeter  501  formed from 72 outer optics  301 . The outer perimeter  501  encompasses all remaining optics  301 . All one hundred and forty-four optics  301  are joined together by a holder  302  to form a common mechanical unit. As depicted, the LED system  101  includes an outer ring  501 , a middle ring  510  and an inner ring  511 . Each ring  501 ,  510 - 511  having a plurality of LEDs. The outer ring  501  containing both the middle ring  510  and the inner ring  511 . The middle ring  510  containing the inner ring  511 . The ring  501  having at least one optic open region  502   a . The ring  510  having at least one optic open region  502   b . The ring  511  having at least one optic open region  502   c . The open regions  502   a - 502   c  allow for air flow. 
       FIG. 5B  depicts a conceptual view of exemplary opening in the optic having at least three optics that form an outer perimeter. At least three optics  503 - 505  form an outer perimeter  506  such that the outer perimeter  506  contains, encircles, or encompasses any remaining optics in the LED system (e.g., LED system  101 ). The optics  503 - 505  may be mechanically isolated or mechanically connect together. For example, the dotted lines may represent portion of a lens holder that mechanically connects at least two of the optics  503 - 505 . Each optic  503 - 505  corresponds to an LED package (e.g., LED package  201 ). The optic open region  508  is formed within the perimeter  506  between the optics  503 - 505 . The optic open region  508  may allow for air flow. 
       FIG. 5C  depicts a conceptual view of an exemplary opening within an outer perimeter. With reference to  FIG. 5B , a second inner perimeter  526  formed by an inner at least three optics  523 - 525  is contained within the outer perimeter  506 . In some embodiments, at least one of the LEDs corresponding to at least one of the optics  523 - 525  is different than at least one of the LEDs corresponding to at least one of the optics  503 - 505 . Each optic  503 - 505 ,  523 - 525  corresponds to an LED package. As depicted, the outer perimeter  506  and the inner perimeter  526  do not cross each other. The optics  523 - 525  may be mechanically isolated or mechanically connected together. For example, the dotted lines may represent a portion of a lens holder that mechanically connects at least two of the optics  523 - 525 . The inner perimeter  526  includes at least one inner open region  528  to allow airflow. The inner perimeter  526 , as depicted, is completely contained within the outer perimeter  506 . The addition of the inner perimeter  526 , with optics, allows for the LEDs to be optimally spread out across the surface defined and bounded by the outer perimeter  506  thus allowing for improved heat dissipation resulting in a more even temperature distribution across the heatsink surface. 
     In some embodiments, at least one optic may be mounted near the perimeter of the mechanics that compose the overall optical system. In various embodiments, at least a portion of the optic may be mounted within 25 mm of the edge of the LED system. With reference to  FIGS. 2A and 3A , the outer ring  323  of optics, corresponds to the outer ring  223  of LEDs. The outer ring  323  may be mounted within 25 mm of the diameter edge of the heatsink  102 . 
     Optical illuminous intensity distribution or optical light distribution is measured in how light is emitted at different angles from a light source. The total possible distribution is into a sphere, also known as four PI steradians (4π). A typical unit for visible light intensity is candela (cd) or lumens (l) per steradians. A typical representation of the light distribution is to slice through the sphere and plot the light intensity in the form of a polar plot where the radial units are in candela. 
       FIG. 6A  depicts a polar plot illustrating an exemplary optical intensity for a Lambertian optical intensity distribution of a raw light output from an LED. A LED emits a light  601  substantially into the lower hemisphere. A center optical axis  602  is at zero degrees) (0°) on the polar plot. For directional lighting applications including high bay, low bay, PAR, MR, BR, AR, the majority of light is intended to illuminate a useful area in front of the optical system in direction of the optical axis  602 . A Useful Region of light  603  is defined as ±50° from the center optical axis  602 . The region above ±50° but below ±90° is defined as the Glare Zone  604 . For the Lambertian distribution, significant light may be in the Glare Zone  604  which is not only wasted but a source of visual discomfort. It is highly desirable to minimize light emitted into the Glare Zone  604  and more efficiently redirect, via an optic, this light into the Useful Region  603 . The Useful Region  603  and the Glare Zone  604  form the lower hemisphere where the majority of light is generally emitted into. The upper hemisphere  605  defines a region called Uplight Zone  605 . The Uplight defines how well a light may illuminate the ceiling. In various embodiments, Uplight may or may not be required. 
       FIG. 6B  depicts a plotted Cartesian light distribution where an x-axis is plotted from 0-90° to show the optical intensity distribution in only one hemisphere. 
     The illuminance profile E(θ), at a plane of interest, is calculated by 
               E   ⁡     (   θ   )       =         I   ⁡     (   θ   )       ·       (     cos   ⁢           ⁢   θ     )     3         h   2             
where an intensity distribution I(θ) in candela at angle θ and h equals the height from the luminaire to a plane where the illuminance is to be calculated. The plane, for example, may be a work surface or a floor. One unit for illuminance is lumens per meter square (l/m 2 ) or lux. Note the illuminance E(θ) from equation
 
                 I   ⁡     (   θ   )       ·       (     cos   ⁢           ⁢   θ     )     3         h   2           
declines rapidly with (cos θ) 3 . In order to have a more evenly illuminance E(θ), optical intensity distribution I(θ) needs to at least partially compensate by increasing in value with θ to counteract the decreases with (cos θ) 3 . In some embodiments, this compensation in I(θ) manifest itself as a peak of the optical intensity distribution I(θ) away from the center axis to an off axis region 15-45°. In various embodiments, the optical intensity results in a relative illuminance profile such that the variation, from center to a relative lateral distance of 0.7 from center, may be at least 40% of the center illuminance. Relative lateral distance is defined as the lateral distance D from the center axis  602  divided by height h, where the lateral distance is D=h·tan θ, and the height h of the LED system As such, the relative lateral distance is simply tan θ.
 
     The optical distribution created by at the at least one LED in combination with at least one optic may determine parameters such as glare, amount of light in the Useful Zone, Uplight, relative illuminance uniformity and level or illuminance. In various embodiments, the optical distribution may satisfy one or more of the following requirements:
         a. The peak of the optical intensity distribution I(θ) is not at the center axis but in a region 15°−40° from center.   b. The optical intensity I(θ) results in a relative illuminance profile such that the variation, from center to a relative lateral distance of 0.7 (tan θ=0.7), is at least 40% of the center illuminance.   c. At least 85% of the total light in the lower hemisphere is in the useful zone.   d. No more than 20% of light is in the glare zone.   e. The maximum candela in the glare zone  604  is no more than 15% of the center axis  602  candela.   f. At least 70% of the total light is in the useful zone  603  and at least 7.5% of light is in the up light zone.   g. At least 5% light is in the Uplight zone.       

       FIGS. 6B-6F  illustrate characteristics of various different optical distributions. The first optical distribution from an existing Acuity HID 400 W fixture. The second optical distribution illustrates an example of an LED Lambertian distribution. The third optical distribution from an LED Gaussian distribution. The fourth optical distribution from an exemplary LED target distribution. The characteristics of these optical distributions are also summarized in Tables 1 to 3. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Luminaire 
                 Lamp  
                 Fixture 
                 Light Loss 
                 Net  
               
               
                 System 
                 Lumens 
                 Efficiency 
                 Factor 
                 Lumens 
               
               
                   
               
             
            
               
                 Acuity HID 
                 40,000 
                  70% 
                 63% 
                 17,640 
               
               
                 LED Lambertian 
                 18,000 
                 100% 
                 85% 
                 15,300 
               
               
                 LED Gaussian 
                 18,000 
                 100% 
                 85% 
                 15,300 
               
               
                 LED Target 
                 18,000 
                 100% 
                 85% 
                 15,300 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Luminaire 
                 % Light in 
                 % Light in 
                 Lumens in 
                 Lumens in 
               
               
                 System 
                 Useful Zone 
                 Glare Zone 
                 Useful Zone 
                 Glare Zone 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Acuity HID 
                 78.5% 
                 21.5% 
                 13,841 
                 3,799 
               
               
                 LED Lambertian 
                 60.3% 
                 39.7% 
                 9,225 
                 6,075 
               
               
                 LED Gaussian 
                 72.6% 
                 27.4% 
                 11,115 
                 4,185 
               
               
                 LED Target 
                 99.7% 
                  0.3% 
                 15,260 
                 40 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Center 
                 Relative Max 
                 Center Lux 
                 Lux Variation 
               
               
                 Luminaire 
                 Candela 
                 Candela in 
                 @ 0° 
                 from Center 
               
               
                 System 
                 @ 0° 
                 Glare Zone 
                 (20 ft Height) 
                 (0-0.7) 
               
               
                   
               
             
            
               
                 Acuity HID 
                 6915 
                 69.8% 
                 186 
                 56% 
               
               
                 LED Lambertian 
                 4740 
                 64.3% 
                 128 
                 45% 
               
               
                 LED Gaussian 
                 7661 
                 33.0% 
                 206 
                 32% 
               
               
                 LED Target 
                 7662 
                  6.9% 
                 206 
                 59% 
               
               
                   
               
            
           
         
       
     
     The first optical distribution is an existing commercial luminaire, Acuity High Bay HID (THD 400MP A15 TB LPI) system. This Acuity HID fixture is used for reference to compare the later three LED systems. As summarized in Table 1, the Acuity HID fixture uses an HID lamp with an initial 40,000 lumens and a reflector with a 30% loss that is used to redirect the light. As such, the Acuity HID has fixture efficiency of 70%. In addition, the Acuity HID Fixture has a light loss factor of 63%. Light loss factor accounts for other loss issues, such as, for example, lamp lumen depreciation or dirt accumulation. Generally HID systems have a much higher lumen degradation than LED systems resulting in the HID having a worse light loss factor, at 63%, than an LED system, at 85%. The net lumens after fixture efficiency and the light loss factor is 17,640 lumens. The Acuity HID optical distribution  610 , as depicted in  FIG. 6B , is calculated based on 17,640 lumens.  FIG. 6F  depicts the cumulative integrated light from on center axis  602  to various angles and provides an indication of the total light in various zones. In the case of the Acuity HID Fixture,  FIG. 6F  and Table 2, illustrate that the Acuity HID optical distribution  650  has about 78.5% in the Useful Zone  603  while 21.5% of the energy is wasted in the Glare Zone  604 . As such, only 13,841 lumens are in the Useful Zone  603  while 3,799 lumens are wasted in the Glare Zone.  FIG. 6C  depicts the optical distribution normalized to a center value. As depicted, the HID normalized optical intensity distribution curve  620  shows that the maximum candela in the Glare Zone  604  is at very high 69.8% of the center candela value.  FIG. 6D  depicts a calculated illuminance in lux at a height equal to 20 feet (h=20). The X-axis is the relative lateral distance from center axis  602  and is calculated as lateral distance divided by the height, or simply tan θ. The HID illuminance  630 , corresponding to Table 3, illustrates a center peak of about 186 lux.  FIG. 6E  depicts the relative illuminance  640  uniformity normalized to the center axis illuminance.  FIG. 6E , and Table 3, illustrate the curve  640  showing the HID optical distribution results in a worst case of a relative illuminance of 56% at relative lateral distance of 0.7. 
     The second optical distribution is an example of a LED system with substantially Lambertian distribution  611  (reference  FIG. 6B ). Such a distribution is typical of a raw LED emission without redirection with an optic. The raw LED output is 18,000 lumens. Accounting for an after the fixture efficiency of 100% and a light loss factor of 85%, the net lumens are reduced to 15,300 lumens. The optical distribution of  611  is adjusted to reflect 15,300 lumens. With reference to Table 2 and the cumulative light curve  651 , the Lambertian optical distribution  611  has significant glare with about 39.7% of light (6,075 lumens) wasted in the Glare Zone  604  and only 60.3% (9,225 lumens) in the Useful Zone  603 . The resulting illuminance  631 , with reference to  FIG. 6D  and summarized in Table 3, has center value of 4740 lux which is significantly lower than the reference case of the Acuity HID of 6915 lux. The Lambertian distribution relative intensity  621 , with reference to  FIG. 6C  and summarized in Table 2, shows a relative maximum candela of 64.3% in the Glare Zone  604  relative to the center intensity. The curve  641 , with reference to  FIG. 6E  and summarized in Table 3, illustrates the Lambertian optical distribution results in a worst case of a relative illuminance of 45% at relative lateral distance of 0.7. 
     The Gaussian optical intensity profile is intended to represent a broad class of intensity profiles. The profile need not to be exactly Gaussian in shape but rather any optical distributions with a peak intensity substantially near a center optical axis of 0° then declining in intensity with higher angles, i.e. moving away from the center optical axis  602 . Such an optical intensity distribution I(θ) cannot compensate for the (cos θ) 3  fall off resulting in an illuminance profile that is generally not very uniform. Broadening the Gaussian cannot compensate for (cos θ) 3 , and may simultaneously lead to very high glare and significant reduction on axis illuminance. The Gaussian like shapes may typically be created with simple optics, such as, for example, simple lens, TIR, or simple reflectors. 
     With reference to  FIG. 6B  and Table 1, the third optical distribution  612  is an example of a LED Gaussian distribution that has been adjusted to reflect 15,300 lumens based on a total of 18,000 lumens discounted by an 100% fixture efficiency and an 85% light loss factor. The Gaussian shape and FWHM was further determined by setting the center peak to 7661 cd to match the fourth distribution  633 . Although the total lumens in this example are the same as the Lambertian distribution, the center peak intensity of 7661 cd is higher than both the Lambertian and the Acuity HID. However, the cumulative light curve  652  (reference  FIG. 6F  and Table 2) shows a relatively high glare of 27.4% of the total light in the Glare Zone  604 . This results in 11,115 lumens in the Useful Zone  603  and 4,185 lumens in the Glare Zone  604 . Also, the relative candela curve  622  (reference  FIG. 6C  and Table 3) shows a relative maximum candela of 33% in the Glare Zone  604 . Although the portion of glare light and maximum candela in Glare Zone  604  may be improved over both the Acuity HID and the Lambertian, the glare is still relatively high. In addition, the improvement in glare comes at the expense of illuminance uniformity. The illuminance curve  632  (reference  FIG. 6D  and Table 3) shows a center illuminance of 7661 lux, but the variation in illuminance  642  from center to a relative lateral distance of 0.7 is about 32% which is worse than both the Acuity HID and the Lambertian. 
       FIG. 6B  depicts a Target LED optical distribution  613  that has been adjusted to reflect 15,300 lumens based on a total of 18,000 lumens in accordance with a 100% fixture efficiency and an 85% light loss factor. Optical distribution  613  illustrates a general class of profiles that represents a preferred embodiment of the optical distribution. This class of profiles simultaneously provide an improved lower glare and an improved illuminance uniformity. The characteristic may be accomplished by partially compensating for the (cos θ) 3  illuminance fall off by increasing the optical intensity distribution I(θ) with angle θ, for certain range of angles. This results in a peak intensity away from a center axis in a region about 15-45° from center. The particular distribution  613  has a peak intensity at about 24°. Another characteristic, the intensity minimizes glare by bringing optical distribution down from the peak to a relatively low value in the Glare Zone  604 . This requires a much steeper roll off in intensity than may be characteristic of either the Lambertian or the Gaussian Intensity Distribution. With reference to  FIG. 6C  and summarized Table 3, the relative intensity  623 , as depicted, is less than 6.9% in the Glare Zone  604  from a peak of about 115% at 24°. This steep roll off occurs within 26°. The result is the cumulative light level curve  653 , as depicted in  FIG. 6F  and as summarized in Table 2, results in about 99.7% (15,260 lumens) of the total light in the useful zone with only 0.3% of the light in Glare zone (40 lumens). The glare may therefore be a significant improvement over optical distribution of Acuity HID, Lambertian or Gaussian. At the same time, as depicted in  FIG. 6D , the illuminance profile  633  is significantly higher over a relative lateral distance 0.7 starting with a center illuminance is 206 lux. In addition, the variation in illuminance from center to a relative lateral distance of 0.7 is about 59% of the center illuminance. Thus, of the four distributions, the Target distribution not only has the lowest glare but also the highest center candela, the highest illuminance, the highest center illuminance and the best illuminance uniformity. The LED Target optical distribution of  613 , with only a raw 18,000 lumens, significantly out performs the legacy Acuity HID fixture with more than twice the raw light level at 40,000 lumens. 
     In some embodiments, the characteristics of the Target optical intensity distribution is preferably achieved using the dielectric CPC optic depicted in  FIG. 6D  or the dielectric CPC optic with the curved output depicted in  FIG. 6E . 
     In some embodiments, the first optical distribution or the Target distribution, satisfies one or more of the following requirements:
         a. The peak of the optical intensity distribution I(θ) is not at the center axis but in a region 15°-45° from center.   b. The optical intensity distribution I(θ) results in a relative illuminance profile such the variation in illuminance from center to a relative lateral distance of 0.7 is at least 40% of the center illuminance.   c. At least 85% of the total light in the lower hemisphere is in the useful zone  603 .   d. No more than 20% of light in the glare zone  604 .   e. The maximum relative intensity in the glare zone  604  is no more than 15% of the center intensity.       

     Heat Sink 
     Heatsinks can be fabricated by multiple processes well known in the arts, such as, for example, diecasting, extrusion, skiving, folded fin, and sheet metal. The heat sink material may include aluminum, aluminum alloys, copper, copper alloys or a thermally conductive plastic. Such thermally conductive plastic can be fabricated from processes such as injection molding that have a thermal conductivity greater than 1 W/M-K. One company that supplies such thermally conductive plastic material is Celanese Corporation. Generally, heatsinks are constructed with a region of elongated features that have a large surface area composing of features such as pins or fins attached to a common base. The large surface area may be used to dissipate heat from the heatsink to the air. These elongated features are generally mechanically held together by attaching them to a common base. In some of the embodiments of this disclosure the base is substantially planar and serves as a mechanical structure where the LEDs and/or Optics are attached. 
       FIG. 7A  depicts a cross section view of an exemplary LED system having a heatsink. A LED system includes a heatsink  701 , at least 3 LEDs  702 , and a series of optics  703  that correspond to the LEDs  702 . The LED  702  are in thermal and mechanical contact with heat sink  701 . The heatsink  701  has a series of elongated features  704 , such as fins or pins, to dissipate the heat generated from the LED  702  to the ambient air. These elongated features  704  are mechanically attached to the heatsink base  706  that is substantially planar. The heatsink  701  having at least one opening such as  712  or  705 . At least three of the outer LEDs  702  forming an outer perimeter  711 . The series of optic  703  have at least one opening  713 ,  707 . The openings  713 ,  707  at least partially overlap at least one opening  705 ,  712  in the heatsink base  706 . Together these openings enable direct and unimpeded airflow flow along from the front of the LED system to the interior of the elongated regions  708 - 709  of the heatsink  701  and thereby improve thermal dissipation. 
       FIG. 7B  depicts a front view of an exemplary LED system having the optic removed for to reveal the LED locations. As depicted, at the LED system includes at least one inner perimeter  721  formed by at least 3 LEDs  720 . At least one of the LEDs  720  forming the inner perimeter  721  may be different than the LEDs  702  forming the outer perimeter  711 . The inner perimeter  721  does not cross cover the outer perimeter  711 . As depicted, the outer perimeter  711  encloses the inner perimeter  721 . Within the inner perimeter  721 , there is at least one opening, such as  712 , that allows for improved air flow. 
     Without such openings  705 ,  707 ,  712 - 713  or open regions  708 - 709 , the air would need to take an indirect path by flowing from front of the heatsink  701  around the edge of the heatsink  701  and then back towards the interior  709  of the heatsink  701 . This indirect circuitous route increases air flow resistance resulting in decreased air flow, and the process of flowing around the heatsink  701  heats up the air such that by the time the air reaches the interior  709  of the heatsink  701  there may be significantly less cooling capacity. The openings  705 ,  707 ,  712 - 713  therefore allow for substantially direct and improved airflow of cool air to the interior of the heatsink elongated region  704  resulting in significantly improved thermal resistance. 
     The air flow also exits  730  the elongated features directly above the elongated features thus enabling the air to flow in a low air resistance path that is substantially in a vertical axis from the front of the LED system to exit behind the LED system. 
     At least one opening  705 ,  707 ,  712 - 713  or open regions  708 - 709  improve air flow and satisfy at least one of the following criteria.
         a. The opening region in the heatsink base, optic and PCB is at least 25% of the outer perimeter area.   b. The improved air flow decreases thermal resistance by at least 5%, 10% or 20% than if such openings  705 ,  707 ,  712 - 713  were covered up.   c. The improved air flow reduces the average temperature of the heatsink by at least 5° C. than if such openings were covered up.   d. The improved air flow reduces the maximum temperature of the heatsink by at least 5° C. than if such openings were covered up.   e. The air flows in a substantially vertical flow path from the front of the optical system through the heatsink base into the elongated features and exiting directly above the elongated features.       

       FIGS. 8A-8F  depict various views of an exemplary LED system having a heatsink with elongated features.  FIG. 8A  depicts an isometric view.  FIG. 8B  depicts an explode view with an optic removed at a distance.  FIG. 8C  depicts a front view of a LED system with an optic removed to show at least three LEDs.  FIG. 8C  depicts a front view of the optic.  FIG. 8E  depicts the front view of the LED system.  FIG. 8F  depicts a cross section L-L of the LED system referenced to  FIG. 8E . A LED system  800  includes a heatsink having a series of pins  803 , a heatsink base  802 , at least three LEDs  804 , an array of optics  820 . The array of optics  820  consisting of at least three optics  824  that correspond to the at least three LEDs  804 . At least three of the outermost LEDs  804  form an outer perimeter  809  from which all the LEDs  804  are contained. Within the outer perimeter  804  there is at least one opening  806 - 805 ,  808  that allows for improved airflow. At least three of the outermost optics  824  form an outer perimeter  829 . Within the outer perimeter  829  there is at least one opening  826 - 825 ,  828  to allow for improved airflow. Each optic  824  corresponds to an individual LED  804 . Optics  824  redirect at least a portion of the raw light output from its corresponding LED  804  into a first optical distribution. The LEDs  804  and optics  824  are described in other parts of this disclosure. The openings in the heatsink  806 - 805 ,  808  at least partially overlap some of the openings  825 - 826 ,  828  in the optic  824 . For example, as depicted in  FIGS. 8E and 8F , the heatsink opening  806  at least partially overlaps the optic opening  826 , the heatsink opening  805  at least partially overlaps the optic opening  825  and the heatsink opening  811  at least partially overlaps the optic opening  821 . Together these openings  805 - 806 ,  808 ,  825 - 826 ,  828  allow for improved and more direct vertical airflow path  831 , 832  from the front  830  of the LED system  800  to the interior of the heatsink elongated features  803  and exiting  840  above the elongated features. The illustrated geometry may allow for the air to flow almost directly and unimpeded from front  830  of the system to the elongated pin feature  803  at the interior  831 , 832  of the heatsink. 
     In various embodiments, the outer LED perimeter  809  includes at least one inner perimeter  810 - 811 , each inner perimeter  810 - 811  is formed by at least three LEDs  804 . At least one of the LEDs  804  forming the inner perimeter  810 - 811  is different than the at least three LEDs  804  forming the outer perimeter  809 . The inner perimeters  810 - 811  have at least one opening  806 , 808  that allow for improved air flow. The inner perimeters  810 - 811  do not cross over the outer perimeter  809  and are enclosed by the outer perimeter  809 . Within the outer optic perimeter  829 , at least one inner perimeter  820 - 821  is formed by at least three optics  824 . At least one of the optics  824  of the least three optics  824  forming the inner perimeter  820 - 821  may be different than at least three optics  824  forming the outer perimeter  829 . The inner perimeters  820 - 821  have at least one opening  826 ,  828  to allow for improved air flow. If these such openings  826 ,  828  are blocked, the air  832  has to flow from front of the heatsink around the edge of the heatsink and then back towards the interior of the heatsink. This indirect circuitous route increases air flow resistance resulting in decreased air flow. This process of flowing around the heatsink base  802  heats up the air such that by the time the air reaches the interior of the heatsink there may be significantly less cooling capacity. The LEDs  804 , as depicted in  FIG. 8C , are substantially evenly distributed across the surface of the heatsink base  802  thus allowing for improved spreading of the heat load. The openings in the heatsink base  802  are also substantially evenly distributed across the surface of the heatsink thus allowing for a more even air flow into the interior of the heatsink. One consequence of more evenly distributing heat load across the heatsink base is the requirement to spread or conduct the heat across the heatsink base is substantially reduced. Rather much of the heat generated by the LEDs may directly conducted backwards to the heat dissipating features without the need for spreading across the base. In some embodiments, the lateral heat spreading across the surface of the base is substantially negligible. The reduced heat spreading requirement of the base i.e. reduced requirement for in plane lateral thermal conductivity allows for the base to be thin and allow for perforation in the heatsink base  802  with openings which reduces weight and improve air flow. In some embodiments, the heatsink base may be from 0.5-4 mm in thickness. In  FIGS. 8A-8F , The LEDs  804  are substantially thermal isolated from each other across the base of the heat sink base  802  and base is only connected by thin slivers  831  between the opening  808  that serves to hold the base as one single mechanical unit than for thermal conductivity across the base. 
     In certain applications, there may be a weight limit for the overall LED system. For example, Underwriters Laboratory (UL) standard 1993, “Self-Ballasted Lamps and Lamp Adapters” Section 5.4 limits the maximum weight up to 1.7 kilograms (kg) for LED Retrofit lamps intended to replace HID lamps with an E39 socket. Such Retrofit Lamps have been described, for example at ([00182]), in U.S. application Ser. No. 14/952,079, titled “LED LIGHTING,” filed by Frank Shum, on Nov. 25, 2015 and at  FIG. 29-30 , of U.S. Provisional Application Ser. No. 62/141,010, titled “LED Lighting,” filed by Frank Shum, on Mar. 31, 2015, the entire disclosures of which are hereby incorporated by reference. Generally, the heatsink may be a significant portion of the weight of an LED system. The LED system also includes the weight of the driver, optics, and driver housing, for example. The heatsink must therefore weigh substantially less than 1.7 kg. In some embodiments, the heatsink weighs less than 1 kg while still being capable for dissipating heat from an optical system generating more than 10,000 lumens. The fabrication process such as die casting or extrusion may require a minimum feature size and or aspect ratio. For example, both die casting and extrusion may have difficulty in fabricating features sizes less than 1 mm or having aspect ratio greater than 10 to 1. The dimensions, and therefore weight, of the heatsink dissipating features, such as fins or pins, may be determined by a fabrication limitation rather than requirements for heat dissipation. As such, the heatsink may be heavier than necessary. 
     In some applications where weight may be critical, sheet metal fins may be preferred. Sheet metal can achieve a thickness less than 1 mm, less 0.6 mm or less than 0.5 mm while simultaneously achieving an aspect ratio great than 20 to 1, or 40 to 1 or 80 to 1. 
       FIGS. 9A-9B  depict various views of an exemplary LED system having sheet metal fins. An LED system  906  includes a heatsink having a series of heat transfer members such as elongated sheet metal fins  901  attached to a heatsink base  902 . At least three of the LEDs  903  are in thermal communication with the heatsink. As depicted, the outer LEDs  903  form an outer perimeter  904 . The outer perimeter  904  includes at least one opening  905  to allow for improved air flow from the front  906  of LED system to the interior  907  of the heat sink. In some embodiments, the LED system includes at least one inner perimeter  914  formed by at least 3 LEDs  903 . At least one of the LEDs  903  forming the inner perimeter  914  is different than the LEDs  903  forming the outer perimeter  904 . The at least one inner perimeter  914  does not cross over the outer perimeter  904  and is enclosed by the outer perimeter  904 . The inner perimeter  914  includes at least one opening  915  to allow for improved and substantially direct and vertical air flow from the front  906  of LED system to the interior  907  of the elongated fins and exiting above the elongated fins  910 . 
       FIGS. 10A-10B  depict an isometric view and a front view of an exemplary heat sink having at least two fins. A heat sink includes at least two fins  1001 ,  1006 , which are substantially the same size, pointing radially to a common center and are in thermal contact to a base  1002 . At least one of the fins  1001 ,  1006  thermally and mechanically attaches to a center column  1011 . At least three of the outer most LEDs  1003 , form an outer perimeter  1004  having at least one opening  1005  formed between the combination of LEDs  1003 , the PCB and the optic to allow for improved air flow. The optional optic and the PCB are not shown. As depicted, the spacing between the fins  1001 ,  1006  at a heat sink perimeter  1009  is larger than the spacing of fins near the center region  1008 . In such a radial arrangement, optimum spacing may be generally difficult to achieve. For example, if fin spacing at the perimeter  1009  is optimized, the fin spacing near the center region  1008  becomes too close (e.g., &lt;3 mm) to allow for effective air flow. In some embodiments, at least one of the LEDs  1003  forming the inner perimeter  1014  may be different from the LEDs  1003  forming the outer perimeter  1004 . The inner perimeter  1014  does not cross over the outer perimeter  1004  and is enclosed by the outer perimeter  1004 . The inner perimeter  1014  includes at least one opening  1015  that allows for improved air flow. 
       FIGS. 10C-10D  depict an isometric view and a front view of an exemplary heatsink having fins of different radial lengths. As depicted, a modification is made to improve the spacing issue by using fins of at least two different radial lengths with a first fin  1001  with a first radial length and a second fin  1010  with a shorter radial length. The shorter fins  1010  are positioned towards the outer perimeter  1004 . In this configuration, the interior fin spacing  1018  is substantially improved over the center region  1008  while the fin spacing at the perimeter  1009 ,  1019  remain substantially unchanged. 
       FIGS. 10E-10F  depict an isometric view and a front view of an exemplary heatsink having an opening in the center. As depicted, a heatsink includes an opening  1012  in the center to allow for further improved airflow. 
     In  FIGS. 10A-10F , the portion of the heatsink base  1002  separated in two mechanical rings corresponding to outer perimeter  1004  and inner perimeter  1014 . The base  1002  itself cannot spread the heat from the outer perimeter  1004  to the inner perimeter  1014  thus the two perimeters are substantially thermally isolated from each other. The majority of the heat generated in each perimeter ring flows substantially directly through the base  1002  backwards into the heat dissipating feature of the fins. By spreading the LEDs  103  into multiple perimeter rings allows for a more even distribution of heat across the front surface of the outer perimeter of base  1002 . Within each perimeter ring  1004   1014 , the LEDs are substantially distributed uniformly across the circumference of the ring, which mean the heat generation along the ring is substantially uniform and temperature is substantially uniform, so heat need not be spread along the circumference of the ring. As the heat generated need not flow laterally, neither radially or along circumference, in base  1002 , the in plane lateral thermal conductivity of base  1002  is greatly reduced. This allow for the base  1002  to be made very thin and perforated with openings  1005   1015  for air flow. The openings  1005 ,  1015  and thinnest of the base  1002  has the additional advantage of allowing the base  1002  to be light weight. 
       FIGS. 11A-11B  depict an isometric view and a front view of an exemplary heatsink. With reference to  FIG. 1B , heatsink  102  includes at least two heatsink fins  1101 ,  1102 , each fin  1101 ,  1102  orientated in a radial pattern. At least one of the fins  1101 ,  1102  is connected thermally and mechanically to either a central column  1103  and, optionally, to a base  1104 . The connection method may include crimping, riveting, brazing, soldering or gluing. In various embodiments, at least one of the fins  1102  may be of a shorter radial length than the other fin  1101 . The short fin  1102  may be positioned towards an outer perimeter. In such an arrangement, the spacing  1105  between fins  1101  from near the center may increase leading to improved airflow and reducing temperature. Another benefit of a shorter fin may be reduced weight. 
       FIG. 11C  depicts an exploded view of an exemplary heatsink. As depicted, the heatsink  102  includes the center column  1103 , a plurality of fins  1101 ,  1102  and the base  1104 . 
       FIGS. 11D and 11E  depicts an exemplary set of a pair of fins. As depicted, fins  1101 ,  1102  are fabricated from a single piece of material, such as sheet metal, and folded into shape. The two fins  1101 ,  1102  are connected by a flat base region  1107 . The flat base region  1107  may be thermally and mechanically attached to the base  1104  or, alternatively, directly to a PCB. If directly attached to a PCB, the preferred method would be a thermally conductive glue, such as, for example, an epoxy, silicone, or thermal grease. In various embodiments, the flat base region  1107  may not be continuous but has openings  1108  between them. These openings  1108  allow for air to flow when assembled into the full heatsink  102 . 
     In some embodiments, the flat metal fins of  FIG. 9A-11E  may have holes. The purpose of this holes allow for air to flow though the fins which is advantageous if the optical system containing the fins is not mounted in a substantially vertical position. For example, if the optical system is at a skewed angle from vertical or lying horizontal. The holes allow for improved air flow in such orientations. In some embodiments, the hole area may be at least 20% of the surface area of any particular fin. 
     Optical Accessory 
     A secondary optic, or optical accessory, may be placed in front of the primary optic to redirect at least a portion of a first optical distribution into an overall secondary optical distribution. In some embodiments, the primary optical distribution may be modified by the optical accessory so the overall secondary optical distribution becomes one or more of the following: wider, asymmetrical, provide uplight, reduce glare such as in using louvers, diffuse the light, suitable for aisle lighting. 
     In various embodiments, the majority of primary light distribution passes through unaltered by the optical accessory. In some embodiments, between 5% and 75% of the primary distribution may be substantially unaltered. In various embodiments, openings, or open regions, in the optical accessory may pass light through the accessory unaffected. Although such open areas can be filled with a flat parallel window which does not substantially alter the direction of light passing through it, such windows still suffer from Fresnel reflection or a 4% back reflection from each of the two surfaces resulting in an about 8% loss in optical efficiency. Therefore, openings formed from an absence of material are advantageous as they provide maximum efficiency without Fresnel losses. Such openings also have the additional benefit of reduced weight and allowing for airflow. 
     In some embodiments, the optical accessory may be substantially round and can be rotated on its center such that any asymmetric secondary optical distribution of the accessory rotates with the accessory. 
       FIGS. 12A-12C  depict various views of an exemplary optical accessory. With reference to  FIG. 1B , the optical accessory  104  may be used to provide uplight. The optical accessory  104  includes an optical portion  1203  that redirects at least a portion of the primary optical distribution. In some embodiments, the optical accessory has an opening  1201  that allows for air flow. In various embodiments, the optical accessory  104  has mechanical attachment features that allow for mounting to a LED system. For example, the mechanical attachment features may include screws, snaps, or magnets. In an illustrative example, the mechanical attachment features enable easy rotation of the optical accessory  104  about its center relative to a LED system. As depicted, the optical accessory  104  is attached to the main structure through a series of snap features  1202 . The snap features  1202  are designed in such a way that allow for easy rotation of the optical accessory  104 . The snap features  1202  are designed to snap into a corresponding feature in the primary optic. 
       FIG. 13A  depicts the front view of an exemplary optical system having an optical accessory. The optical accessory  104  over laps and redirects at least a portion of the light from the outer ring of optic  323 . The opening  1201  in the optical accessory  104  allows for light from the middle ring  322  and the inner ring  321  to escape undisturbed. The opening  1201  further enables air flow to the optic opening  502 , the LED opening  205  and into the interior of the heatsink  102 . The opening  1201  may also reduce the weight of the optical accessory. 
     In some embodiments, for the creation of uplight, there is at least one LED at a periphery near the edge of the mechanics. The mechanics may comprise the optical system or the heatsink  102 . The optical accessory creates up light by redirecting a least a portion of light emitting from the at least one LED at the periphery to create the up light. In various embodiments, a LED and a corresponding optic may be within 25 mm of an edge of the LED system that does not have the optical accessory. Advantageously, locating the LED near the edge of the mechanics may more easily allow for the redirection of at least a portion of light around the mechanics into uplight. In various embodiments, between 5% and 40% of the total light from the LED system is redirected into uplight. The optical accessory may have interior opening so that majority of the light passes through it unaffected. 
       FIG. 13B  depicts a cross section view of an exemplary optical system having an optical accessory. The cross section, at F-F, includes the heatsink base  1305 , a PCB  1303 , at least one LED package  1302 , a primary optic and the optical accessory  104 . The primary optic includes at least one optic  1301 , an optic holder  1306 , and a mating snap feature  1304 . 
       FIG. 13C  depicts an illustrative optical ray trace of a cross section of an exemplary optical system. The LED  1302  is located near the perimeter of the mechanics of the optical system. The mechanics compose an optical system such that a portion of an emitted light may be more easily redirected by the optical accessory  104  around the mechanics to form uplight  1310 . At least one portion of the emitted light from the LED  1302  is redirected by the optic  1301  into a first distribution  1315 . At least a portion of the first optical distribution  1315  is further redirected by the optical accessory  104  into an overall secondary distribution comprising of the unaffected light  1309  and the redirected light  1310 . In some embodiments, the primary optic  1301  may be in the form of a dielectric CPC with an input surface  1314 , a TIR reflector surface  1307  and a curved output surface  1308 . The optical accessory  104  includes an input surface, a first reflector surface  1313 , a second reflector surface  1312  and an exit surface  1316 . The input surface and the exit surface  1316  may share a portion of the same physical surface. The optical accessory  104  has series of snap features  1202  designed to mate to the main optical system via corresponding features in the optic  1304 . The snap features  1202  may be designed in such a way to allow for easy rotation of the optical accessory  104  by hand. 
       FIG. 14  depicts perspective view of an optical accessory. An optical accessory, as depicted, may be used to redirect a light into a more asymmetric profile. The optical accessory having at least two different regions, a first region  1403  and a second region  1404 . Each region arranged to redirect the light into substantially different distributions. The optical accessory further comprising an open region  1401  having similar function to the open region  1201 . The optical accessory includes a snap feature  1402  having similar function to snap feature  1202 . 
       FIG. 15  depicts a top perspective view of an exemplary optical accessory having an additional optical accessory region  1501  that is used to redirect the light from the interior of corresponding LEDs. The additional region  1501  may have an opening region  1502  to allow for improved air flow into the LED system. 
     In some embodiments, the optical accessory may be stackable so at least a portion of light may be redirected by each optical accessory. 
     Electronic Driver 
     The LED systems may be powered from at least two types of sources, such as, for example, directly from offline AC voltage source or from a ballast. 
     In the case of offline operation with AC voltage source  1701 , the electronic LED driver may be powered by AC line voltages including 100 VAC to 480 VAC and including frequencies 50 Hz or 60 Hz. Some popular voltages include 100, 110, 115, 120, 200, 220, 230, 208, 240, 277, 305, 380, 400, 415 or 480 VAC. The electronic driver technology for such offline supplies include switching mode drivers with various topologies, such as, for example, buck, boost, buck bust, flyback, or combinations thereof. 
     In the case of operation with a ballast, such as a magnetic HID ballast, certain challenges need to resolved, for example achieving an acceptable power factor (PF) and a total harmonic distortion (THD) at the input to the ballast. Additionally, preventing damage from pulse start ballasts with ignitors that generate approximately 2-5 kV pulses during the initial warm phase intended for an HID lamp may also need to be resolved. Examples of Pulse start 400 W HID ballast with ignitors include M135, M155, or SD51. An example of Probe start 400 W HID ballast without ignitors includes M59. 
     HID magnetic ballasts are designed for specific HID lamp load. For example, a M59 magnetic ballast is designed to power 400 W metal halide HID lamp with good power factor, generally &gt;0.9 or &gt;0.8 and a good THD, generally less than 32% or less than 20%. A LED lamp intended to directly retrofit to with the same HID ballast would require significantly less power, for example consume 150 W instead of 400 W. This presents a completely different load to ballast and may result in a poor power factor, for example a power factor less than 0.8, and a poor THD, for example a THD greater than 32%. The LED electronic driver must operate to trick the ballast in delivering a significantly lower power of about 150 W or about 200 W while maintaining a good PF and a good THD to the system. 
       FIG. 16A  depicts a schematic of an exemplary 400 W Probe Start Metal Halide ballast designed to work with a probe start M59 Metal Halide lamp load. A ballast  1601  includes a transformer  1606 , an output capacitor  1605 , a series of inputs  1602  and an output  1603 . The series of inputs  1602  includes multiple taps into the transfer allowing the ballast  1601  to operate at different AC voltage sources, such as 277V, 240V, 208V or 120V. In an illustrative example, a Metal Halide lamp load  1604  may be replaced with an electronic driver through a connection  1703 . During the initial operation of a HID lamp, where the HID lamp is in a cold state, the HID lamp has high impedance and the ballast  1601  operating in a relatively constant wattage mode delivers about 300V to the HID lamp. As the HID lamp warms up, the impedance drops resulting in a drop in voltage to about 130 V. 
       FIG. 16B  depicts a schematic of a 400 W Pulse Start Metal Halide ballast designed to work with pulse start M135 Metal Halide lamp load. A ballast  1611  includes a transformer  1616 , a capacitor  1615 , a series of inputs  1612  and an output  1614 . The series of inputs  1612  includes multiple taps into the transfer allowing the ballast  1611  to operate at different AC voltage sources, such as 480V, 277V, 240V, 208V or 120V. The Metal Halide lamp load  1614  may be replaced with an electronic driver through the connection  1703 . The initial high impedance of a HID lamp in a cold state results in an initial higher voltage across the lamps, for example, V i &gt;250V. The high voltage may be sensed by ignitor  1620  and causes it to generate 2-5 kV pulses to help expedite the warm up of HID lamps. Once a HID lamp warms up, the impedance drops to about 130V. The ignitor senses this drop in voltage and ceases firing. 
       FIG. 17  depicts a schematic of an exemplary electronic LED driver designed to interface with a magnetic ballast. A magnetic ballast  1702  (e.g., ballast  1601  or ballast  1611 ) is powered by an offline AC voltage source  1701 . The ballast  1702  is connected to the electronic LED driver  1704  via an electrical connection  1703 , for example an E39 or E40 lamp base. The electronic LED driver  1704  includes a capacitor  1708 , a rectifier bridge  1707 , a smoothing capacitor  1708 , and optional current and/or thermal fuses  1705 . The electronic LED driver  1704  powers LED  1709  with forward voltage V f . The input capacitor  1706 , disposed before the bridge, needs to be bipolar, such as a film type capacitor. The input capacitor  1706  serves as a partial shunt that diverts some of the output power and current from ballast  1702  back into the ballast  1702  instead of to the LED  1709 . The smoothing capacitor  1708  is intended to minimize the current ripple going into the LED  1709 . The power and LED forward current I f , into the LED  1709 , is controlled by the combination of the capacitance in capacitor  1706  and the LED  1709  forward voltage, V f . A M59 ballast, with an input capacitor  1706  of about 22 uF and a LED with forward voltage of about 140V, will result in approximately 150 W delivered to the LED  1709 . The value of the smoothing capacitor may be set to 1000s uF. In such a configuration, at the input to the ballast  1702 , the PF is about 0.89 with a relatively high THD, at 48%. 
     In some embodiments, the input capacitor  1706  may be reduced to 10 uF and the LED  1709  forward voltage V f  may be reduced to between 65V-75V. This results in an improved power factor of 0.92 and a significantly improved THD of 23% with power, about 200 W, delivered to the LED  1709 . The load voltage experienced by the ballast output is substantially equal to the LED forward voltage, which is well below the voltage needed for the ignitor to fire Voltage V i  of about 250V. Thus, in such an arrangement, the electronics driver components are protected from the ignitor high voltage pulses. 
     The LED  1709  has a forward Voltage V f  and a LED current I f . The LED  1709  may be the previously referenced LED  101  that is part of the overall LED system  100 . 
       FIG. 18  depicts a schematic of an electronic LED driver designed to interface with a magnetic ballast. The electronic LED Driver having a bridge, a switch controlled by a controller unit, a smoothing capacitor and a string of LEDs with total forward voltage V f . With reference to  FIG. 17 ,  FIG. 18  consists of the addition of a switch  1802  controlled by a controller unit  1803 . The switch  1802  may be a MOSFET, or any other device or combination of devices that have relatively low impedance when activated and have a current carrying capacity for at least a portion of time to shunt the power and current back into the ballast  1702 . The switch  1802  may be designed to selectively shunt a portion of the power and current from the ballast  1702  back to ballast  1702  thereby regulating the power into the string of LEDs  1709 . The controller unit  1803  may have selective sensor inputs. The selective sensor inputs may include a LED current from current sensor  1805 , the output voltage V B  from rectifier bridge  1707 , a voltage across capacitor  1708 , a temperature of the string of LEDs  1709  or a temperature of the electronic LED driver  1801  itself. The controller unit  1803  senses these inputs and controls the switch  1802  accordingly to regulate the LED forward current I f . The controller unit  1803  may simply be a selection of discrete components or more flexibly be a microprocessor or micro controller unit. If the controller unit  1803  is able to sense the phase of the input voltage, such as, for example, by monitoring the voltage V B  across the bridge  1707 , switching can be in phase or synchronous with the line frequency. In some embodiments, the controller unit  1803  may control the switch  1802  regardless of phase or in heuristic control manner that is asynchronous with the input voltage waveform. 
     The main purpose of the controller unit  1803  is to the control switch  1802  in a manner that regulates the LED current to some predetermined manner. One advantage of  FIG. 18  over  FIG. 17  is that the controller  1803  can regulate current I f  to the LED  1709  more precisely to accommodate variations in the line voltage V s . For example, V s  commonly varies at ≧10% and the controller unit  1803  can sense the LED current I f  and adjust the switch  1802  to maintain a substantially predetermined current level. Further, when the temperature of the system exceeds some predetermined value, either for safety or to prolonging the life of the system, the controller unit  1803  can reduce the current to the LED  1709  thereby reducing the heat generated regulate the over temperature, a feature known as thermal roll back. Another advantage of the controller unit  1803  may be configured to dim the system when less light is required. 
     In reference to  FIG. 18 , and assuming a constant supply voltage V s , the ballast  1702  may supply substantially a constant ballast current I Ballast  over a range of Ballast loads. Table 4 summarizes the maximum power delivered to the LED (I f ·V f ), using the schematic of  FIG. 18 , where ballast  1702  is a M59 HID ballast and switch  1802  is in an open state. By leaving switch  1802  in an open or deactivated, none of the current from the ballast is shorted back to itself, instead all the current is sourced to LED (I f =I Ballast ) which allows the determination maximum possible delivered power to the LED. In Table 4, the current I f  is substantially constant with changing LED forward voltage V f  resulting in the power delivered to the LED to be substantially proportional to the LED forward voltage V f . If there is no variation in ballast input voltage V s  and no variation in the components such as the ballast or LEDs, the system power can simply be maintained by setting the LED forward voltage and there is no need for incorporation of switch  1802  or controller  1803 . In reality, the AC source voltage can vary by at least +/−10% which leads to a ballast current to vary approximately proportionally or I Ballast αV s . Also, the ballast may vary from unit to unit and with aging which also affects the ballast current I Ballast . The addition of switch  1803 , and  1802  compensates for such variations. The activation of switch  1803  can only decrease the delivered LED power from the maximum possible delivered power, so it is necessary to set the LED forward voltage V f  such that the maximum possible deliver power is higher than the nominal power. In the nominal situation, the switch activates with the required duty cycle to reduce the delivered power to the desired nominal level. For example, in the case of Table 4, assume the nominal desired power is 175 W and assume the ballast current can vary I Ballast =2.6 A+/−15%. The system would be designed such the maximum possible power level at the nominal ballast current would be at least 15% greater than 175 W or about 201 W. This would correspond to a minimum required LED forward voltage of about V f ≧79.8V. To deliver only 175 W at V f =79.8V, the LED forward current need to be regulated to about 2.19 A instead of 2.6 A (175 W=79.8V·2.19 A). This may be accomplished by controller  1803  monitoring the LED forward current I F , using current sensor  1805 , and producing an appropriate duty cycle in switch  1802  such that average LED forward current is controlled to about I f =2.19 A, with the excess current bypassed by the switch back to the ballast. In such a scenario, the switch is always switching under nominal conditions with an appropriate duty cycle to maintain a LED forward current I f  less than the ballast current I Ballast  i.e. I Ballast  (2.6 A)&gt;I f  (2.19 A). However, if I Ballast  fluctuates away from it nominal current of I Ballast =2.6 A to I Ballast &lt;2.19 A, the switch can no longer regulate the LED current to I F =2.19 A, as at most can LED current I F  only be equal the ballast current to I B . Thus, to be able to maintain regulation around the nominal condition, at the nominal operating point, the LED forward current I f  must always less than the ballast current I Ballast  (I f &lt;I Ballast ), and switch  1802  is always switching to maintain this condition. In some embodiments at nominal operation conditions the LED current satisfy I f &lt;0.95 I Ballast  or I f &lt;0.9 I Ballast  or I f &lt;0.85 I Ballast    
     There are least four possible advantages of having the switch  1802  and controller  1803 :
         a. Maintains LED current to a predetermined level even there is a fault or variations in the system, including if the wrong ballast is used to power the LED electronic driver.   b. With an addition of a temperature, the switch can be used to reduce the LED current to maintain a predetermine temperature. This is especially important for example in a fault condition the abnormally raises the system temperature.   c. The switch can reduce current for dimming of the LED output.   d. The switch allows for a less stringent specification of the LED voltage as long as the LED voltage is above a minimum required value.       

     
       
         
           
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 LED Forward 
                 Ballast 
                 Maximum Possible 
               
               
                 Voltage 
                 Current 
                 Power to LEDs 
               
               
                 V f   
                 I Ballast   
                 I Ballast  · V f   
               
               
                 (Volts) 
                 (Amps) 
                 (Watts) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 59.1 
                 2.66 
                 157 
               
               
                 61.8 
                 2.61 
                 161 
               
               
                 64.8 
                 2.60 
                 168 
               
               
                 67.7 
                 2.58 
                 175 
               
               
                 70.7 
                 2.55 
                 180 
               
               
                 73.6 
                 2.55 
                 188 
               
               
                 76.7 
                 2.53 
                 194 
               
               
                 79.8 
                 2.53 
                 202 
               
               
                   
               
            
           
         
       
     
     In some embodiments, the controller unit  1803  also regulates the LED current while improving the PF and/or THD at the input to the ballast. 
     In various embodiments, the system consists of a HID ballast, an electronic driver, and a LED string. The HID ballast may have a set of inputs powered by an AC voltage source and a set of outputs to power the electronic driver. The ballast sourcing a ballast current I Ballast  at its output. The electronic driver having at least a rectifier and a switch. The rectifier inputs are connected to the ballast output and the rectifier output is connected to the LED string. The switch being connected in parallel across the bridge output and across the LED string such when the switch is deactivated, the ballast current I Ballast , substantially flows to the LED string and when the switch is activated, the switch substantially shorts the LED so the ballast current I Ballast  is diverted through the switch back the ballast thus bypassing LED string. The switch is switched in a pattern to maintain a desired forward current I f  into the LED. The LED forward voltage is set to a minimum value, such that under nominal conditions the average ballast current is always less than the LED forward current, I f &gt;I Ballast . In some embodiments, there may also be a temperature sensor and the switch is switched in a pattern to reduce the current into the LED and to maintain a predetermined temperature set point. In further embodiment, there may be a capacitor across the LED to smooth out the current ripple and a diode before the capacitor to block the capacitor current flowing back to the switch. 
       FIG. 19  depicts possible methods by which a controller unit controls a switch. A scheme  1910  shows the equivalent rectified offline voltage source  1701  or V s . Note the rectified bridge voltage V B , will have same periodicity as the scheme  1910  but may of a different, non-sinusoidal shape due to distortion from a ballast. Nevertheless, the bridge voltage V B  may be used to sense the periodicity of the offline voltage V s  which may be of a fixed phase offset. Schemes  1920 - 1970  show possible schemes to control the switch  1910  relative in timing to the phase of rectified voltage  1910  to regulate the LED current with possible benefit to improve PF and/or THD at the input to the ballast. 
     In scheme  1920  and  1930 , the switch  1802  is controlled in phase or with a fixed phase offset with rectified voltage V B    1910 , and there is a single on/off cycle within each cycle of the rectified voltage V B    1910 . As such, the frequency of the scheme  1920  is the same as the scheme  1910  which is twice the line voltage frequency Vs  1701 . The scheme  1920  is symmetrical within the cycle whereas a scheme  1930  is intended to represent a class of schemes where the pulse of an arbitrary shape need not be symmetrical within the cycle. By intentionally offsetting the pulse from the peak of the voltage, the load can crudely be made to seem to be inductive or capacitive thus such pulse pattern is intended to improve PF or THD at the input to the ballast. The pulse pattern may also be used to simulate a nonlinear load to generate harmonics to cancel out harmonics in the ballast to overall improve THD. In some embodiments, the equivalent impedance, whether linear or nonlinear may vary within the duty cycle. Such control scheme is later described with reference to  FIGS. 23-25 . 
     In scheme  1940 , the switch  1802  is controlled in phase or with a fixed phase offset with rectified voltage V B , but there is not a full on/off cycle of the switch  1802  within each cycle of the rectified voltage V B , thus the frequency of the scheme  1940  is lower than the scheme  1910 . 
     In scheme  1950 , the switch  1802  is controlled in phase or with a fixed phase offset with rectified voltage V B , but there is more than a single on/off cycle of the switch  1802  within each cycle of the rectified voltage V B . Thus, the frequency of 1940 is higher than 1910. In some embodiments, the frequency may be 2×, 4×, 10×, 100×, 1000×, 10,000× that of the rectified line frequency or alternative &gt;10 KHz. One advantage of a higher frequency system is it more regularly charges the capacitor  1708  thus reducing the required capacitance. In various embodiments, the switching frequency may be equal or great than 2× the rectified line frequency but still of a sufficiency low frequency, for example less than &lt;10× rectified line frequency, such that the inductance the output of the ballast does not impede the shutting of current back to the ballast. For example, a typical inductance of the output winding of a M59 ballast is about 1000 mH. In other words, the ballast output may have sufficient inductance that if the switch  1802  is operated at too high a frequency, it may not effectively shunt the current and power from the ballast back into the ballast. 
     In scheme  1960 , the switch  1802  is controlled out of phase with rectified voltage V B . This scheme  1960  may more broadly encompass the switch patterns and frequency of the  1920 - 1950  but out of phase with rectified voltage V B  of the scheme  1910 . Such a class of asynchronous control include heuristic control, for example only switching as necessary to keep the voltage or current controlled to some predetermined range. Such a control scheme  1960  is simpler in that the complexity of sensing the phase, then syncing to the phase of the input voltage is not needed. 
     In scheme  1970 , the switch  1802  controlled in phase with rectified voltage V B  of the scheme  1910 , but the switching pattern is intended to be arbitrary within each period but repetitive in each subsequent period. For example, in the specific scheme  1970 , the frequency is higher at the beginning of the cycle and changed smoothly to a lower frequency. Such a scheme will more precisely simulate capacitive or inductive needed to improve PF and THD at the input to the ballast. 
       FIGS. 20A-20F and 21A-21D  depict various schematic of an exemplary single LED driver specifically designed to be able to be power by either a magnetic ballast or directly with the offline AC source V s . Such an implementation has the advantage in that a single product can address both types of power sources. However, this increases complexity as the driver must resolve one or more of the following issues:
         a. Achieve acceptable PF and low THD for both types of power sources. Acceptable PF for example may be &gt;0.7, &gt;0.8 or &gt;0.9. Acceptable THD for example may be &lt;50%, &lt;32%, &lt;20%.   b. Prevent damage from a ballast containing ignitors that may fire high voltage pulses.   c. Sense the type of power source to configure both in hardware or software the type of control schemes to accomplish # 1  or # 2  above.       

     In  FIGS. 20A-20F and 21A-21D , a set of dotted lines is used to indicate when the AC offline voltage source  1701  is connected to the driver input connection  1703  and a set of solid lines are used to indicate when the ballast  1702  is connected to the driver input connection  1703 . Note, it is not intension to connect both the AC Offline voltage source  1701  and the ballast  1702  simultaneously to the driver  2001  input connection  1703 . 
     In  FIG. 20A , the electronic driver  2001  has a switch  2002  that is similar to prior switch  1802 , and a controller  2003  that is similar to prior controller  1803  and includes all the control and switching schemes  1920 - 1970 , but this time rather than regulating the current I f  in the LED  2009 , the combination of controller  2003  and switch  2002  may be designed to regulate either the voltage or current entering regulator  2010 . The regulator  2010  may then be used to regulate the current I f  to LED  2009 . A diode  2011  is prevents current from the regulator  2010  flowing backwards through switch  2002 . The regulator  2010 , for example, can be a switching mode regulator, such as, for example, a buck, boost, buck boost, fly back or combination therefore including multiple switching stages. Alternatively, the current regulator  2010  can be a linear regulator. An optional current sensor  2016  may measure the current going through the switch  2002 . 
       FIG. 20B  shows a possible embodiment of  FIG. 20A  where the regulator  2010  consists of a first stage including a diode  2011 , a capacitor  2008  and a second stage regulator  2011 . The regulator  2011  has regulated voltage V SC  at its input. Controller  2003  regulates voltage V SC . By using a two-stage method of  20 B, the voltage regulation of V SC  need not be very tight. For example, if the regulator  2011  is a buck boost current regulator, the input V SC  may vary, for example, either higher or lower than the LED forward voltage V f . 
     In an embodiment for  FIG. 20B , the maximum regulated voltage at V B  should always be less than the ignitor trigger voltage V i , by doing so, the ignitor may be prevented from firing its high voltage pulses. For example, if the controller  2003  senses the bridge output voltage V B  is approaching ignitor trigger voltage V i , then the switch  2002  may be activated to short, for at least a portion of time, in a manner to ensure the V B &lt;V i . During the portion of time the switch  2113  is activated, the switch  2113  substantially shorts the bridge output voltage V B  to be near 0V which is less than the ignitor trigger voltage. 
     In some embodiments, the current regulator  2011  is a buck regulator. The voltage V sc  across the capacitor  2008  is substantially regulated by the controller  2003  and switch  2002  to be higher than the LED  2009  forward voltage V f  but less then ignitor trigger voltage V i  preventing the ignitor from firing. 
     In another embodiment of  FIG. 20B , the capacitor  2008  is designed to have the necessary capacitance to absorb a sufficient amount of energy from the ignitor pulse to bring down the peak pulse voltage to an acceptable level that do not damage the driver components which is generally below the voltage rating of the components. As an example, we can calculate the necessary capacitance C 2008  to sufficiently absorb the pulse energy from a M59 ballast ignitor by using the following parameters about the ballast: M59 output winding inductance is about H B =1 Henry or 1H, M59 output short circuit current is about I SC =4 A, the maximum voltage at the ballast output is about V Z   _   M =250V, and the voltage rating of the capacitor  2008  is about V R =450V. Then the necessary capacitance C 2008  is given by the following formula: 
     
       
         
           
             
               C 
               2008 
             
             ≥ 
             
               
                 
                   I 
                   SC 
                   2 
                 
                 · 
                 
                   H 
                   B 
                 
               
               
                 
                   ( 
                   
                     
                       V 
                       R 
                     
                     - 
                     
                       V 
                       
                         Z 
                         ⁢ 
                         _ 
                         ⁢ 
                         M 
                       
                     
                   
                   ) 
                 
                 2 
               
             
             ≥ 
             
               
                 
                   4 
                   2 
                 
                 · 
                 1 
               
               
                 
                   ( 
                   
                     450 
                     - 
                     250 
                   
                   ) 
                 
                 2 
               
             
             ≥ 
             
               256 
               ⁢ 
               
                   
               
               ⁢ 
               uF 
             
           
         
       
     
     Note the voltage rating of the capacitor  2008  also needs to also be sufficient to accommodate the worst case offline voltage. For example, if offline voltage source has a nominal RMS voltage V s =277 VAC with a maximum 10% over voltage then the voltage rating of the capacitor V R  needs to higher than the peak of this AC line under worse or:
 
 V   R ≧277·1.1·√{square root over (2)}≧431V
 
     Therefore, a capacitor with a voltage rating of 450V will be suitable for being powered by both an offline voltage source Vs=277V and by a M59 ballast. 
     In other scenarios, the capacitor  2008  has a capacitance C 2008 ≧100 uF, ≧200 uF or ≧500 uF with a voltage rating V R ≧200V, ≧450V or ≧750V. Such large capacitance values are generally much larger than typically present in EMI filters with capacitance on the order of &lt;10 uF or &lt;1 uF. 
     One advantage of correctly sizing the capacitor  2008  with sufficient capacitance is it will be able to continuously sustain ignitor pulses, for example in circumstance where controller  2003  or the current regulator  2012  cannot guarantee V B &lt;V i . Such circumstances may include, if the control circuit is missing, malfunctions, disabled or there is noise, surges in the power line. 
     In various embodiments, the controller  2003  may be designed to activate the switch  2010  if the rectified bridge  1707  voltage V B  is sensed to be approaching or be above a certain level limit voltage V c , such as, for example, V c &gt;200V, V c &gt;250V, V c &gt;300V. It is desirable the limit voltage V c  is less than the ignitor trigger voltage V i  to suppress the ignitor in the ballast from firing. The switch  2002  stays in an activated shunt position until such a time it will not cause the ballast output voltage to rise above the ignitor trigger voltage, V i . For example, an energy storage unit in the regulator  2010 , such as the capacitor  2011 , may sufficiently drain to a level where the opening of the switch  2008  will cause the charging of the energy storage unit. In such a condition, the charging of the storage unit will result in a relative low impedance in the regulator  2010  resulting in a lower voltage V B  that should be below the ignitor trigger voltage or V B &lt;V i . 
     One key issue may be the switch  1705  of  FIGS. 20A-20B  needs to be deactivated (off) or in a high impedance mode, when the driver  2001  is directly connected to the offline voltage source  1701 , otherwise it will short circuit the line voltage and cause the fuse or other components  1705  to exceed their current rating. This can be prevented if the controller  2003  can sense if the driver is connected to ballast  1702  or directly connected to offline voltage source  1701 . In some embodiments, this sensing is accomplished by monitoring the current I s , using current sensor  2010 . The short circuit current I s  will be significantly higher when connected to offline voltage source  1701 , I s (offline), than when connected to Ballast, I s (ballast). In other words, I s (offline)&gt;&gt;I s (ballast). For example, the short circuit ballast current I s (ballast) for a M59 ballast I SC (ballast)≈4 A RMS or 7 A Peak, whereas, assuming Vs=120V AC and a switch resistance of 5 ohms, the short circuit current of the offline voltage source I s (offline)≈24 A RMS or 32 A peak which is significantly higher than I SC (ballast)≈4 A. The sensing should occur within a relatively short time period, for example &lt;0.25 seconds, &lt;0.5 seconds, &lt;1 second, or &lt;2 seconds during the initial power up of the driver to prevent the potential of a short circuit current in switch  2002  from damaging the driver in the case it is connected to offline voltage source  170 . 
     When the electronic driver of  FIG. 20B  is operated directly from the offline voltage source  1701 , the switch  2002  is deactivated and the system is essentially a regulator  2012  with a large capacitor on the front. Generally, such a capacitor on the input side of the driver results in poor PF and poor THD performance. In a further improvement, as depicted in  FIG. 20C , the capacitor  2008  has a series switch  2026 . The switch  2026  is controlled such that when powered from a ballast  1702 , the switch  2016  switches the capacitor in parallel with the regulator  2012 . When powered directly from an offline power  1701 , the switch  2016  switches out the capacitor to improve PF and THD performance. 
     In an alternative embodiment to improve PF and THD, as shown in  FIG. 20D , the capacitor  2008  of  FIG. 20B  is replaced with a Valley Fill capacitor arraignment consisting of capacitors  2014 ,  2013  and diodes  2015 . The advantage of such a system, the switch  2016  may not be required thus reducing complexity. Another advantage may be that total voltage rating for the capacitor  2018  is reduced and split between capacitor  2014  (V C2 ) and  2013  (V C1 ) so each individual capacitor can be of a lower rating. However, the individual capacitance values of the capacitors  2013 ,  2014  needs to increase such that their combination in series is similar to total required capacitance of the capacitor  2008 . 
     In an alternative embodiment, as shown in  FIG. 20E , the switching associated components  2002 ,  2003 ,  2010  are intentionally removed such that the system is a regulator  2012  with a valley fill circuit front end. The advantage of such a system may be reduced complexity as no switching (outside of regulator  2012 ) may be needed and the system does not need to sense if it is powered by a ballast or powered directly to offline voltage source. The disadvantage may be without the switch  2002  to shunt the power, the PF and THD of the system will likely suffer. 
       FIG. 20F  shows an improvement to  20 E, where the capacitor  2017  is placed in front of bridge. The benefits of the capacitor  2017  include improved THD, PF when operating with a ballast, and a reduced peak from the ballast. The capacitor  2017  is similar in specification and performs the same function as already described for the capacitor  1706 . For example, the capacitor  2017  needs to be bipolar, such as a film type capacitor, and serves as a partial shunt that diverts some of the output power and current from the ballast  1702  back into the ballast  1702  instead of to the components after the bridge. 
     The valley fill circuitry shown in  FIGS. 20D-20F , and elsewhere referenced, in this document can be modified further to improve THD and PF by using the modifications shown in  FIGS. 20G-20H . A resistor  2018  may be added to the Valley Fill Circuitry.  FIG. 20H  shows a further improvement of a version of a Valley Fill Circuitry where two additional capacitors  2019 - 2020  are added with a center tap  2021  that is connected to the input side of the bridge. The capacitors  2019 - 2020  may maintain current flow during a longer portion of the voltage cross over and thereby improve PF and THD. To fill in the cross over point requires only a very small amount of power so the capacitance value of the capacitors  2019 - 2020  may be of a magnitude smaller than the capacitors  2013 - 2014 . A resistor  2022  in series with the capacitor  2013  may be added to reduce current spike. Such a circuit may be capable of PF&gt;0.9 and THD&lt;20%. 
     The function of the Valley Fill circuitry, previously described, to be capable of at least one or more of the following functions:
         a. Sized with sufficient capacitance and voltage rating to absorb the pulses from an ignitor when operated from a ballast, such as ballast  1702 .   b. Sized with sufficient capacitance to smooth out the voltage V SC  to the current regulator  2012 .   c. Improve PF and THD operation when operated directly from an offline AC voltage source  1701 .       

     The following summarizes the embodiments of  FIGS. 20A-20H . A LED driver that may be powered by least two different external power sources, the first power source being a ballast and the second power source being an AC voltage source. The LED driver including a bridge rectifier, the input of the bridge connected to the external power source, the output of the bridge connected in parallel to a switch, and also in parallel with a regulator. A regulator may be designed to regulate the current to one or more LEDs. 
     In some embodiments, the sensing the presence of either the ballast or the AC voltage source occurs with a predetermined length of time after the power up of the system. A sensor detects the presence of either the ballast or the AC voltage source. The sensing occurs during the power up of the system. The switch may be deactivated or in a high impedance mode when AC voltage source is detected. If a ballast is detected, the switch periodically activates according a predetermined scheme to regulate the current or the voltage going into the current regulator. 
     In various embodiments, at least one equivalent capacitor may be connected in parallel with the bridge output. The capacitor may be of sufficient capacitance to absorb the pulses from an ignitor such that the resulting pulse voltage is reduced &lt;500V. The equivalent capacitor may be arranged in a Valley Fill circuit arrangement. In some embodiments, the switch and its associated circuitry may be removed. 
     The driver  2001  of  FIGS. 20A-20H  may include further elements, not shown, such as EMI filters, PF correction or THD correction circuitry. For example, a simple EMI filter includes a PI filter having 2 capacitors arranged in parallel to bridge output with either one or both sides of the capacitor connected by one or more inductors. The EMI filter can be placed before and after the bridge rectifier. 
       FIGS. 21A-21D  depict various schematics of an exemplary electronic LED driver designed to be powered by a ballast or to be powered directly with the offline AC source. In the prior implementations of  FIGS. 20A-20D , the switch  2002  may be designed to deactivate or be in a high impedance when connected directly to the offline AC source  1701  so that the regulation of the LED current I f  is taken over by current regulator  2010 , whereas in  FIGS. 21A-21D , the switch  2112  in combination with the controller  2113  is implemented to regulate the LED current when powered by ballast  1702  or powered directly by the offline AC source  1701 . As such, the switch  2112  may not be deactivated when powered to offline AC source  1701 . 
       FIG. 21A  depicts the LED driver  2101  having a switch mode regulator  2115 , the bridge  1707 , optional temperature and/or the current fuse  1705 , a EMI filter  2114 . The EMI filter  2114  can be placed after the bridge as shown or before the bridge, or both. The switch mode regulator  2115  regulates the forward current, I f  to LED  1709 . The switch mode regulator  2115  includes at least one equivalent inductor  2114  and a switch  2112  controlled by controller  2113 . The switch  2112  and the inductor  2114  are connected in such a method that, at low frequency (e.g., DC to 240 Hz), will substantially shunt or short current from the one side of the bridge back to the return side of the bridge. This is necessary in the case of being powered by a ballast and is an example of switching mode topologies (e.g., Boost, Buck-Boost, SEPIC, CUK, Flyback, Forward, Push-Pull, half bridge, resonant LLC) that will shunt the output of the bridge at low frequencies. However, a boost topology will not accomplish this. The combination of the inductor  2114 , the switch  2112  and the controller  2113  substantially regulate the current I f  to the LED  1709 . In some embodiments, there may be at least two distinct schemes to control the switch  2112 . A first scheme when powered with a ballast  1702  and a second when directly power with the offline AC source  170 . In various embodiments, there may be a third switching scheme during initial power up of the system. The third switch scheme may be used to achieve at least two functions: The first function may be to detect if the power source may be the ballast  1702  or an offline AC voltage source  1701 , and the second function may be to ensure there is not an over current short circuit situation when hooked to the offline AC voltage source  1701  or alternatively an overvoltage situation when powered by ballast  1702 . For example, when the system powers up, the system connects to an offline AC voltage source  1701  and switches at a relatively high frequency, for example a switch scheme with substantial frequency content &gt;10 KHz where the inductor  2114  at the frequency content is specified at a value that has non-negligible impedance and served to limit the maximum current. As such, a short circuit current may be prevented, as would be the case with a low frequency switching scheme that would short circuit and damage the system. However, if the detected current, either through the switch  2112  or the controller  2113 , is not as would be expected from an offline AC voltage source  1701  then the controller will change the switching scheme to that used for a ballast, such as, for example, a switching scheme with substantial frequency content &lt;10 KHz or &lt;1 KHz or &lt;240 Hz. The lower frequency may be necessary as the ballast output winding will have an impedance value significantly higher than the inductor  2114 , for example &gt;10×. As such, the inductor  2114  becomes negligible and the switching frequency content necessary to function with the ballast may be substantially lower, for example, 10× lower than the case with the offline voltage source  1701 . The switching scheme both for high and low frequency include those already described in  FIG. 19 , such as those intended to improve PF and THD. 
     The EMI filter  2114  includes at least one of the following two functions: a first function of filtering out EMI and EMC noise from a regulator and a second function absorbing the pulses from the ignitor in the ballast such the resulting pulse are at an acceptable value. A portion of the EMI filter may compose of a Valley Fill circuitry. 
     In  FIG. 21B , the regulator  2115  is configured in the form similar to a boost converter where the inductor  2114  is connected before the switch  2112 . When the controller  2113  senses the electronic driver is directly powered by an offline AC source  1701 , it switches the switch  2112  to a high frequency as would be expected in a switching mode power supply, for example &gt;10 kHz. The entire unit performs as a boost converter where the inductor  2114  has non-negligible impedance. However, when the controller  2113  senses it is connected to the ballast  1703 , the controller  2113  switches at a much lower frequency, for example &lt;10 KHz, &lt;1 KHz, &lt;240 Hz or for example, at 120 Hz. At this lower frequency, the inductor  2114  is of substantially negligible impedance and the system sustainably operates the same as depicted in  FIG. 18 . When operating in a boost converter mode the LED voltage must always be higher than the peak voltage of input offline AC source  1701 . In the event where the offline voltage source  1701  is Vs=277 VAC, the peak voltage is 391V so the LED string must be greater than the voltage which would require many LEDs to be string together. Another issue may be the higher voltage has more stringent component and safety requirement. 
       FIG. 21C  shows an improvement to  FIG. 21B  where diode  2120  is added to connect the output of the bridge  1707  to the capacitor  2108  so that in the event that a pulse is generated by the ballast  1702 , the diode  2111  conducts this energy to the capacitor  2108  to at least partially absorb the energy to an acceptable level. The calculation for the necessary capacitance for the capacitor  2108  is the same as previously described with reference to  FIG. 20B . One advantage of this arrangement may be that the capacitor  2108  is after the switch  2112  and the inductor  2114 , rather than directly at the input as in case of  FIGS. 20B-20F , and the switch  2112  in combination with the inductor  2114  can be configured to switch in such a manner to optimize for PF. 
       FIG. 21D  shows the implementation of the regulator  2115  in the form of a SEPIC with addition of the capacitor  2117  and the inductor  2118 .  FIG. 21E  shows the implementation of the regulator  2115  in the form of a CUK converter with addition of the capacitor  2117 , the inductor  2119 , and the diode  2111  removed and replaced with diode  2120  in a new position. 
     In  FIG. 22 , the electronic driver  2101  is configured in the form similar to a flyback converter with the addition of the transformer  2214 . The switch  2112  is connected in series with the input winding of the transformer  2214  and connects the transformer output winding to return or ground. The transformer input winding serves a dual function as the inductor  2114  as described previously. When the controller  2113  senses the electronic driver  2101  is directly connected with the offline AC source  1701 , it switches the switch  2212  at higher frequency as would be expected in a switching mode power supply, for example &gt;10 kHz. The entire unit performs as flyback converter where the transformer  2214  has non-negligible impedance. However, when the controller  2113  senses to the ballast  1703 , the controller  2113  switches at a much lower frequency, for example &lt;10 KHz, &lt;1 KHz, &lt;240 Hz or, for example, at 120 Hz. At this lower frequency, the inductor  2114  may be of a substantially negligible impedance and the system sustainably operates the same as  FIG. 18 . 
     In a further embodiment to  FIGS. 21A-21E , when connected to a ballast, the controller  2113  controls the switch  2112  in a combination of at least two substantially different frequency content, a higher frequency component  2330 ,  2332  and a lower frequency component  2331 . The lower frequency component  2331  may be sufficient to shunt a portion of the power and current from the ballast back into the ballast thereby bypassing the LED. The lower frequency component  2331 , for example, &lt;10 KHz, &lt;1 KHz or at 120 Hz, being at the such a lower frequency than the impedance of the inductor  2114 , or the equivalent inductor of the first winding of the transformer  2214 , may be negligible. The higher frequency component  2330 ,  2332  is sufficient to effectively transfer power to the LED through the transformer  2214  or the inductor  2114 . The higher frequency for example may be &gt;10 kHz. In some embodiments, the controller  2113  ensures the output voltage of the ballast  1703  or that the bridge voltage V B  is always below the voltage that triggers the ignitor in the ballast, for example, &lt;200V, &lt;250V, &lt;300V. 
     The trace  2320 , as depicted in  FIG. 23 , shows the equivalent rectified offline voltage source  1701  V s  or the rectified ballast output voltage V z . Note the rectified bridge voltage V B , will have the same periodicity the line voltage V s , but may be of a different and non-sinusoidal shape due to distortion from ballast. Nevertheless, the bridge voltage V B  may be used to sense the periodicity of the offline voltage V s . The schemes  2321 - 2322  are examples of how the controller  2113  may be used to control the switch  2112  in the presence of a ballast  1702 . Both schemes  2321 - 2322  have at least two distant frequency components, a lower frequency component  2231  intended to shunt the power and current from the ballast, and a higher frequency component  2231  intended to transfer power across the transformer  2214  or the inductor  2114 . 
       FIG. 22  depicts a preferred implementation of an electronic driver that is both compatible with an offline voltage source  1701  and with a ballast  1702 . A fly back topology provides isolation and a flexible LED forward voltage may not be dependent on the source voltage at the input to the driver. 
     The following summarizes the illustrations depicted in  FIGS. 21A-21E  and  FIGS. 22-23 . A LED driver that can be powered by least two different external power sources, a first external power source being a ballast and a second power source being an AC voltage source. The LED driver includes a bridge rectifier, the input of the bridge connected to the external power source, the output of the bridge connected switch in series with an inductor. A sensing mechanism that detects the presence of either the ballast or the AC voltage source. The sensing occurs during the power up of the system. A switch may be activated by at least two different switching patterns, a first switching pattern when powered by a ballast and a second switching pattern when powered by an AC voltage source. The switch activation pattern shorts the inductor to the bridge return and may be designed to regulate the current into the LED for both power sources. The first switching pattern to have a lower frequency content than content than the second switching pattern. 
       FIG. 24A  depicts a control arrangement for an LED driver  2421  that incorporates power factor correction. The power conversion circuit  2420  is constructed such that its input current is forced to be substantially proportional to the signal V c . In this case the signal V c  is created by the multiplication between the rectified voltage V B  and the error signal V Error  or V c =(V B ·V Error ) or I in α(V B ·V Error ). The equivalent resistance R D  the driver presents to the AC source  1701  is R D  a R D αV B /I in  which simplifies to R D α1/V Error . The V Error  signal can be kept to a relatively constant average value by filtering its frequency content with a low pass filter  2411  such that it changes at a rate that is much lower than the AC input frequency (bandwidth of the filter  2411 &lt;60 Hz/10 for example). If V Error  is kept relatively constant, then the equivalent resistance R D  will also be relatively constant. The output current feedback  2116  adjusts the V Error  Signal to keep the LED string current I f  at a constant value as set by the LED current set point  2410  or V IS . Some other components in the system include  2414  a sensor detect the rectified line voltage, a multiplier  2412 , an input current sensor  2405  and a LED current sensor  2105 . The power conversion circuit may have energy storage components such capacitors that is used to store input current for a portion of the AC line voltage cycle, then later releasing the stored energy to the LED in another portion of the AC line voltage cycle. The power conversion circuit may be capable to present very high impedances similar to an open circuit or very low impedance such a short circuit. 
     In  FIG. 24B  the inclusion of a waveform generator  2413  is used affect the signal V c . In such an arrangement, the control arrangement becomes capable of presenting real and reactive and non-linear impedances to at the electronic driver  2431  input  1703 . For example, the input current may be shifted in phase with respect to the input voltage V B , making the driver appear as a parallel combination of capacitance or inductance and resistance to the ballast. The waveform generator can also generate harmonics of the power line frequency resulting in a nonlinear load. This allows the input current to be any wave shape by summing the correct harmonics components. This may be advantageous when the electronic driver  2431  is connected to a ballast as the ability to present an inductive, capacitor or nonlinear to load may be used to improve power factor or THD at the input to the ballast. To further improve PF and THD, the impedance, linear and/or nonlinear need not be constant but change within a half cycle of the line frequency. The higher harmonic nonlinear load presented to the ballast may be necessary to cancel out the harmonic distortion created by the ballast which may not be possible purely linear reactive, capacitive or resistive impedances. 
     The control scheme described for driver  2431  may be implemented using topologies similar to electronic driver  2001  or  2101  where the power conversion circuit composes of at least a switch similar in function as switch  2002  or  2112  and where the waveform generator  2413  may result in power conversion circuit  2420  to switch with waveforms similar to  FIG. 19 . 
     The optimal current wave shape or non-linear impedance to optimize the input power factor and distortion of the ballast may be set by the waveform generator. If the waveform generator is configured to provide the input voltage or a scalar multiple of the input voltage to the multiplier the control arrangement of  FIG. 24B , it then may become functionally equivalent to the control arrangement of  FIG. 24A . This arrangement can therefore be configured to operate from a ballast or directly from the AC line. 
       FIG. 25  shows a process for selecting the operational mode of the driver and for configuring the control circuit for optimal ballast input power factor and harmonic distortion for multiple ballast types. When the driver first wakes up after application of input power it begins by testing the input impedance of the AC source to determine if it connected to the AC grid (low impedance) or to a ballast (high impedance). If input power is determined to be provided by a ballast the configuration is set for a typical ballast. Further testing of the ballast impedance is then done to determine which ballast type is present. The ballast type is then used to set the specific transfer function for optimal power factor and distortion at the ballast input 
     Electronic Accessory 
     In one embodiment of the LED system, there is an Electronic Accessory located in the front center portion of the LED system, an optimum location for the Electronic Accessory as: 
     a. This is at airflow inlet thereby experiencing the coolest air. 
     b. The front surface generally has unobstructed view of the area of interest which is useful if the electronic accessory is, for example, a visible or infrared camera. The front also allows unobstructed emitting and receiving of wireless signals, for example, radio frequency such as WiFi, Bluetooth, Z-Wave, Thread, Zibgee or other wireless signals. The front surface is also particularly advantageous for unobstructed optical communication signals such as LiFi to and from the lighting system. 
     c. The center location allows for an optical accessory with a center opening to be easily placed over the electronic accessory and rotate around the accessory without interference. 
     In some embodiments, the electronic accessory has electrical connections to draw power from the main lighting unit including 12V, 5V or 3.3V. Another set of electrical connections may send a dimming signal, for example 0-10V, PWM back to dim the main LED system. There may also be data communication lines using protocols such as SPL, I2C, SPI in order for the electronic accessory to communicate with the main lamp assembly. The electronic accessory further has wireless communication capabilities to receive data to dim the light. The wireless unit may also emit data signals to communicate with other lighting system as well to a control unit. 
     In other embodiments, the electronics accessory may also contain one more sensors such as day light sensors, occupancy, temperature, GPS location, world clock, altitude, humidity, vibration, acceleration. 
     A further embodiment of the GPS may include high sensitivity or ultra-sensitivity that allows for an accurate location within buildings. A GPS sensor may be highly advantageous in combination with wireless communication as it allows the LED system to report back its position. This may be highly advantageous for occasions such as in initial setup or commissioning of the systems where the location of the lamps is needed, for example, identifying certain lamps controlled within which zones. This may be also paired with other remote sensors in addition to an optional GPS sensor to more easily determine for which sensors control which lights and within which zones. Without GPS, the location of every sensor and led system must be manually recorded during the initial installation and marked onto some floor plan. With the proposed GPS sensor, both the lighting locations and or other optional sensors can be automatically generated. 
     In some embodiments, the electronics accessory may contain one or more display lights. Such display lights may communicate some information, such as, for example, need for maintenance, replacement, fault condition, availability of a parking spot, location of an item in a warehouse etc. 
     In various embodiments, the electronics accessory may contain one or more audio elements, such as, for example, speakers, microphones, or buzzers. Such audio elements may be useful, for example, in a public announcement (PA) system. 
     In some embodiments, the electronic accessory may be stackable so that additional electronic functions may be added. In such a stacked arrangement, it may be advantageous that the electrical interconnections are arranged so they also be easily stacked like a LEGO block. 
     Although various embodiments have been described with reference to the Figures, other embodiments are possible. For example, in the embodiment of  FIGS. 8A-8F , the heatsink base  802  may thermally connect to the pins  803  to define a thermally conductive path extending proximally along a heat transfer axis that defines an axial fluid communication path (e.g., airflow paths  831 ) to conduct heat generated by the LED source substantially proximally to exhaust to ambient atmosphere. In the embodiment of  FIGS. 9A-9B , the elongated sheet metal fins  901  thermally attach to the heatsink base  902  to define a thermally conductive path extending proximally along a heat transfer axis defining an axial fluid communication path (e.g., vertical air flow from the front  906  of LED system to the interior  907  of the elongated fins and exiting above the elongated fins  910 ) to conduct heat generated by the LED source substantially proximally to exhaust to ambient atmosphere. 
     In the embodiment of  FIGS. 10A-10F , spacing between the fins  1001 ,  1006  at an outer perimeter  1004  is larger than the spacing of fins  1001 ,  1006  near the center region  1008  to define a thermally conductive path extending proximally along a heat transfer axis that defines an axial fluid communication path to conduct heat generated by the LED source substantially proximally to exhaust to ambient atmosphere. In the embodiment of  FIGS. 10C-10D , the first fin  1001  has a first radial length and a second fin  1010  has a shorter radial length. The fins  1001 ,  1010  are arranged to define a thermally conductive path extending proximally along a heat transfer axis defining an axial fluid communication path to conduct heat generated by the LED source substantially proximally to exhaust to ambient atmosphere. 
     In  FIGS. 11A-11E , the fins  1101 ,  1102  thermally connect thermally and mechanically to either the central column  1103  and/or to the base  1104  such that one or more thermally conductive paths extend proximally along a heat transfer axis that defines an axial fluid communication path to conduct heat generated by the LED source substantially proximally to exhaust to ambient atmosphere. 
     In some embodiments, the construction of a heatsink, such as the heatsink of  FIGS. 8A-11E , may require less metal thereby reducing the weight of a LED system. The heatsink may, advantageously, have more airflow passageways when compared to a conventional LED system to minimize impedance. In various embodiments, the heatsink may increase the operating life of a LED system because of the heatsink may lower the operating temperature of the LED system. In some embodiments, the LED system may be optimized for vertical orientation by providing a substantially straight path for air to flow. 
     In various embodiments, with reference to  FIG. 2C , the outer perimeter  216  may define a first polygon and the inner perimeter  226  may define a second polygon such the first polygon encompasses the second polygon. In some embodiments, the outer perimeter  216  may share a portion of the outer perimeter  216  with a portion of the inner perimeter  226  such that the first polygon shares a boundary with the second polygon, for example, as depicted in  FIGS. 8D and 9A . 
     In some embodiments, a first plurality of LEDs may be projected unto a first plane while a second plurality of LEDs may be projected unto a second plane. In various embodiments, the first plane and the second plane may be the same plane. In various embodiments, the first plane and the second plane may be substantially parallel to each other and may not intersect each other such that when viewed from a top perspective, the LEDs defining the first plane encompass the LEDs defining the second plane. 
     In various embodiments, an LED-based lighting system with enhanced convective through-flow in an approximately vertical orientation may include a light generation module comprising a plurality of LED sources arranged to illuminate along an optical axis in a distal direction. The plurality of LED sources may be spaced apart from each other by one or more open regions. For each one of the plurality of the LED sources of the light generation module may include a heat transfer member in substantial thermal communication with the LED source such that the heat transfer member has a thermally conductive path extending proximally along a heat transfer axis that is substantially parallel to the optical axis. When in operation, the heat transfer member conducts heat generated by the LED source substantially proximally. The LED-based lighting may further include an optic module having a plurality of optics spaced apart from each other by one or more optic open regions such that each optic corresponds to at least one of the LED sources. Each optic open region may correspond to one of the open regions when the optic module is aligned with the light generation module. The open regions defining at least one or more apertures such that the at least one or more optic apertures defined in the one or more optic open regions aligns with a corresponding one or more apertures in the open region to define an axial fluid communication path through the one or more apertures and the one or more optic apertures, the axial fluid communication path parallel to the optical axis to remove heat from one or more of the heat transfer members, wherein each of the axial communication paths extends proximally to the exhaust to ambient atmosphere. 
     A number of implementations have been described. Nevertheless, it will be understood that various modification may be made. For example, advantageous results may be achieved if the steps of the disclosed techniques were performed in a different sequence, or if components of the disclosed systems were combined in a different manner, or if the components were supplemented with other components. Accordingly, other implementations are contemplated.