Patent Publication Number: US-2012044675-A1

Title: Elongated LED Lamp

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 61/375,937 filed on Aug. 23, 2010, the disclosure of which is fully incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to elongated LED lamps that may replace elongated fluorescent lamps. 
     BACKGROUND OF THE INVENTION 
     Elongated and typically linear lighting is used in various ways, ranging from lighting products in a vending machine or a refrigerated showcase in a supermarket, to lighting surfaces of a desk or under a cupboard. Traditionally, linear illumination devices include cold cathode tubes, neon tubes and fluorescent tubes. Fluorescent lighting devices have been generally desired by most businesses because of their electrical efficiency and their ability to provide uniform lighting. However, fluorescent tubes require high voltages and power, resulting in power usage of several tens of watts per meter. Such high voltages require additional electrical insulation of the fluorescent tube and extra care while handling the tubes. Repairs of fluorescent lighting devices can be costly for both parts and labor. Moreover, the lifetime of a fluorescent lamp is not very long, resulting in need to frequently change them. Sometimes, in a large supermarket, an employee is dedicated only to replacing burned-out fluorescent lamps in the display cases. 
     Recently, light emitting diodes (hereinafter “LEDs”), are being used as alternative forms of lighting. LEDs provide many advantages in lighting. They require less energy than a fluorescent lamp. They also do not produce any significant amount of infrared light in their light beam as a byproduct of their operation. However, many available LED lamps suffer from various drawbacks. For instance, when the number of LEDs required to achieve adequate illumination is reached in many available elongated LED lamps, the illumination creates a pixilated look and multi-shadowing on an illuminated surface. Also, the heat that is generated by the LEDs must be conducted away from the LEDs to ensure proper functioning of the LEDs. 
     Another problem with some prior art LED lighting fixtures is that the fixtures often overheat. It is necessary to provide for the LED lighting fixtures to dissipate its waste heat into the surrounding structure of the lamp. If such provisions are inadequate, the LED will overheat and undergo irreversible damage, which shortens the LED&#39;s useful life. In many prior art arrangements, all the heat is concentrated at the site of the LED. It is therefore desirable to reduce the local heat load of each LED to increase its useful life and/or reduce the size of the associated cooling structures. 
     There is a need for an elongated LED lamp that can replace fluorescent tubes, while avoiding the pixelated look and multi-shadowing on an illuminated surface present in some LED lamps. 
     SUMMARY OF THE INVENTION 
     In one preferred example, an elongated LED lamp, comprises: an elongated side-light distribution arrangement comprising at least three sequentially arranged side-light distribution portions, a plurality of LED light sources respectively associated with said portions by having one LED light source primarily illuminating a respective portion, via a light coupling means, when the central axes of light emission from each of the LED light sources are not aligned with each other and by having one or a spaced pair of LED light sources, each located at an end of the portion, primarily illuminating a respective portion, via a light coupling means, when the associated LED light sources have central axes of light transmission aligned with each other; and each respective light coupling means transforms at least 15% of received light into an appropriate angular distribution needed for total internal reflection within an associated side-light distribution portion. 
     Beneficially, the foregoing elongated LED lamp can replace fluorescent tubes, while avoiding the pixelated look and multi-shadowing on an illuminated surface present in some LED lamps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages and features of the invention will become apparent from reading the detailed description of the invention below in conjunction with the drawing figures, in which: 
         FIGS. 1A and 1C  are respective top and a side views of a prior art lighting fixture showing LEDs located throughout the fixture. 
         FIG. 1C  is a cross sectional view of a prior art lighting fixture showing LED&#39;s located throughout the side-light distribution member. 
         FIG. 2  is a side plan view of an exemplary elongated LED lamp. 
         FIG. 3  is a side plan view of another exemplary elongated LED lamp. 
         FIG. 4  is a side plan view of still another exemplary elongated LED lamp showing respective pairs of a LED light source and a coupling means. 
         FIG. 5  is a cross sectional view of the LED lamp of  FIG. 4 , taken at arrows  5 ,  5  in  FIG. 4 . 
         FIG. 6  is a side plan view of another exemplary elongated LED lamp. 
         FIG. 7  is a cross sectional view of the LED lamp of  FIG. 6 , taken at arrows  7 ,  7  in  FIG. 6 . 
         FIG. 8  is a perspective view of the LED lamp of  FIG. 6 . 
         FIG. 9  is a side-plan view of a further exemplary LED lamp. 
         FIG. 10  is a cross-sectional view of the LED lamp of  FIG. 9 , taken at arrows  10 ,  10  in  FIG. 9 . 
         FIG. 11  is a side plan view of another exemplary elongated LED lamp. 
         FIG. 12  is a cross-sectional view of the LED lamp of  FIG. 11 , taken at arrows  13 ,  13  in  FIG. 11 . 
         FIG. 13  is a side plan view of a further exemplary elongated LED lamp 
         FIG. 14  is a cross-sectional view of the LED lamp of  FIG. 13 , taken at arrows  14 ,  14  in  FIG. 13 . 
         FIG. 15  is a side plan view of a yet another exemplary elongated LED lamp. 
         FIG. 16  is a cross-sectional view of the LED lamp of  FIG. 15 , taken at arrows  16 ,  16  in  FIG. 15 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The examples and drawings provided in the detailed description are merely examples, which should not be used to limit the scope of the claims in any claim construction or interpretation. 
     In the figures, various dimensions have been enlarged for clarity of explanation, such as a typical diameter of an LED lamp compared to its length. 
     Led Light Source 
     A LED light source is defined herein as one or more LEDs provided with a single pair of power leads and, typically also, a single lens for conditioning light output, and includes a printed-circuit board on which an LED or LEDs are mounted, which may have a metal core to assist in heat removal. 
     Prior LED Lighting Fixtures 
     Prior art  FIG. 1A  shows a prior art elongated LED lamp  200  that replaces a fluorescent tube. Many small LED light sources  204  are arranged in an array along the length of the lamp  200 . The array is on a circuit board (not shown) that is electronically connected to input power using electrode pins  201 . 
       FIG. 1B  shows a side view of the prior art lighting device of  FIG. 1 . 
     In  FIG. 1C , a cross-sectional view of the prior art light device of  FIG. 1A . 
       FIG. 1A  shows the cylindrical nature of the replacement LED lamp  200  having a transparent sleeve  202  as well as the width of the heat sink  205  on which &amp; LED light sources  204  are affixed. The heat sink  205  occupies approximately the full inner diameter of the transparent sleeve  202 , and, as with the other heat sinks described herein, may comprise aluminum or other thermally conducting material. 
     Central Path of TIR Light Propagation 
     In one example, the central axis of light emission from a respective light coupling means that receives light from a respective LED light source, is oriented transverse to a central path of total internal reflection (TIR) light propagation through an associated side-light distribution portion, such as in  FIG. 4 , where TIR represents total internal reflection. In another example, a central axis of light emission from a respective LED light source is positioned so that a central axis of light emission is aligned with a central path of TIR light propagation through an associated side-light distribution portion, as would be apparent to a person of ordinary skill, as in  FIGS. 2-3 , for example. 
     In one example, a respective light-extraction means is positioned in a direction opposite to an associated LED light source, as shown in  FIG. 13 , for example, with respect to a central path of light propagation along the length of a respective side-light distribution portion. This length would be the longest path, which would be linear length for a linear side-light arrangement. The length would be the longest non-continuous path that ends in a curve, for a curved arrangement. 
     The central path of light propagation of a respective side-light distribution portion is not shown in the respective FIGS. but would be readily apparent to a person of ordinary skill. 
     Discontinuous Side-Light Distribution Portions 
       FIGS. 2 and 3  show elongated LED lamps  300  and  400 , respectively, each of which contains an exemplary number of four side-light distribution portions  314 . Lamps  300  and  400  can replicate a typical length of a fluorescent lamp tube of about four feet (122 cm), and preferably provide an equivalent amount of illumination. 
     Compared to an LED lamp having only one LED at one end or LEDs at both ends, the LED lamps  300  and  400  have LED light sources  318  whose area is reduced proportionately. Based on the law of Etendue, as the area of the light source is reduced, the diameter of the light coupling means and the side-light distribution arrangement becomes proportionately reduced to maintain the angular distribution of light propagating through the system. 
     In the LED lamp of  FIG. 2 , each of LED light sources  318  supplies light to an associated light coupling means  311 ; “light coupling means” are described in more detail below. Each LED light source  318  is supported on an associated heat sink  320 . Each light coupling means  311  couples light into an associated side-light distribution portion  314 , which may be affixed to a support  308  with brackets  312 . Light-extraction means  310  are provided on side-light distribution portions  314  for extracting light from the side of the lamp  300 . “Light-extraction means” are described in more detail below 
     The LED lamp  300  of  FIG. 2  has end plates  304  that support electrode pins  302 . A transparent protective sleeve  306  protects the side-light distribution portions  314  and associated parts shown within the sleeve. 
     The elongated LED lamp  400  of  FIG. 3  contains like-numbered parts as in lamp  300  of  FIG. 2 , whose description with regard to  FIG. 3  is thus omitted. However, the orientations of the side-light distribution portions  314  in relation to the LED light sources  318 , for instance, differ as between  FIGS. 2 and 3 . For instance, in the center of the LED lamp  400  of  FIG. 3 , two LED light sources  318  are positioned adjacent to each other, with each having a respective heat sink  320 , an arrangement not present in LED lamp  300  of  FIG. 2 . 
     Advantageously, the amount of materials and the weight of the LED lamps  300  and  400  of  FIGS. 2 and 3  can be reduced by a factor of four over a prior art configuration having a single LED light source for a single side-light distribution portion while still delivering an equivalent amount of illumination. The thermal load on each LED light source  318  in this case can be reduced by a factor of four. In another embodiment, the number of side-light distribution portions is greater than the four shown in  FIGS. 2 and 3 . For instance, up to 10 or more side-light distribution portions may be used, with corresponding gains in optical and thermal requirements. 
     In between each side-light distribution portion  314  of the embodiments of  FIGS. 2 and 3 , there may be a small area of darkness because the side-light distribution portions  314  and LED light sources  318  of adjacent fragments cannot overlap in space. Sometimes, the dark spaces are desirable as a way to accent the light and show decorative marks along the length of the lamps. If these are not desired, then a different embodiment of the claimed LED lamp, as shown in  FIG. 4 , for example, will minimize or eliminate the dark areas. 
       FIGS. 4 and 5  show elongated LED lamp  600  having LED light sources  601  whose central axes of light emission pass into associated light coupling means  602  in such a way that the central axes are not aligned with each other, and are instead oriented transverse to a central path of TIR light propagation though side-light distribution arrangement  610 . This contrasts with the light sources in  FIGS. 2 and 3 , for instance, in which the central axes of light transmission are aligned with each other. 
     A respective light coupling means  602  couples received light from each LED light source  601 , which is supported on a heat sink  603 . Each side-light distribution portion  609  of the side-light distribution arrangement  610  is primary illuminated by a respective pair of LED light source  601  and light coupling means  602  connected thereto via a respective connecting portion  604 . Each side-light distribution portion  609  can receive light from an associated LED light source  601  directly or by TIR light propagation within a light coupling means  602  and associated connecting portion  604 . The connecting portions  604  may not maintain the angular distribution of light received from the light coupling means  602 . 
     Light is extracted from each of the side-light distribution portions  609  by respective light-extraction means  605 . Residual light that is not extracted from the side-light distribution arrangement  610  on a first pass through the arrangement can be reflected back into the arrangement by mirrors  607 , which are supported by support structures  608 . 
     Each LED light source  601  is connected by wires to a power-regulating circuit  606 , with such wires shown diagrammatically in  FIG. 4 . Power-regulating circuit  606 , shown diagrammatically, converts AC power from electrodes (not shown) in a fluorescent lighting fixture, which engage the left-shown electrode pins  611 , to DC power with a preferably constant DC current. The power-regulating circuit  606  is preferably physically placed between the left-shown electrode pins  611  and the LED light source  601 . In addition, a transparent protective cover  612 , connected to end plates  611  extends along the length of the LED lamp  600 . 
     The connecting portion  604  is constructed to keep the light internal to itself through the use of TIR. The connecting portions  604  are in optical contact with the side-light distribution portions  609  so no light is lost as light moves from the connecting portion  604  to the side-light distribution portion  609 . “Optical contact” occurs when two surfaces are in optical contact, and light traveling from one surface to the next surface does not experience a reflection as it leaves one surface and enters the next surface. Either the medium through which the light passes is the same or has substantially the same refractive index. Ideally, the connecting portion  604  is constructed from the same material as the light coupling means  602  and the side-light distribution portion  609 . 
     In the embodiment of  FIGS. 4 and 5 , the amount of illumination emitted by the side-light distribution portions  609  may be increased by projecting more light into the side-light distribution portions without increasing their diameter, provided that no one light source  601  and light coupling means  602  pair violates the constraints of the law of Etendue. One advantage of this configuration is that the small dark areas, as present in the embodiments of  FIGS. 2 and 3  are eliminated. 
     In yet another embodiment of the claimed invention, distributing the total LED light sources along the length of a side-light distribution arrangement can provide thermal benefits since there are separate sites over which to distribute the fixed thermal load.  FIGS. 7-16  show such embodiments. 
     Continuous Side-Light Distribution Portions 
       FIG. 7  shows an exemplary circular cross-section for the LED lamp  700  of  FIGS. 6-8 , but other cross-sectional shapes may be utilized. Light-extraction means  702  may consist of a Lambertian scattering material such as white paint or a specular reflecting material such as a metallic material or coating. Further details of light-extraction means are described below. Light-extraction means  702  may run continuously along the length of the side-light distribution arrangement  701  or it may be segmented in various patterns depending on the desired illumination effect. Light-extraction means  702  direct light out of the side-light distribution arrangement  701  as shown by light rays  705 . The LED light sources  703  can be mounted on a heat sink  704 . 
     In  FIGS. 6-8 , the side-light distribution arrangement  701  can have the light-extraction means  702  running along its length. Each LED light source  703  is positioned in a direction transverse to the main path of TIR light propagation through the side-light distribution arrangement  701 . 
     As best shown in  FIG. 7 , the LED light sources  703  can be received partially or completely within the side-light distribution arrangement  701 . Preferably, the entire light-emitting surface of the LED light sources  703  is received within respective cavities in the side-light distribution arrangement  701 . The side-light distribution arrangement  701  inherently performs some angular transformation of the light it receives, at least 15% of received light, to support TIR propagation through side-light distribution arrangement  701 . This is due to an increase in area experienced by many light rays  705  travelling from the LED light sources  703  into the side-light distribution arrangement  701 . 
     Each LED light source  703  may be mounted to a heat sink  704  for dissipating heat from the light source. The LED light source  703 , in another instance, can be optionally connected to a different mounting structure. 
     The light from the LED light sources  703  is guided towards the light-extraction means  702  by the inherent light coupling means mentioned above. In this example shown in  FIG. 7 , the side-light distribution arrangement  701  includes a plurality of portions, each associated with a respective LED light source  703  and which primarily receives it light from that light source. 
     The light-extraction means  702  distributes the illumination from the LED light sources  703  so as to be able to create an evenly distributed illumination. An exemplary spacing of the light-extraction means  702  can be best seen in  FIG. 7 , which shows that such means  702  exists at two locations spaced apart on the circumference of side-light distribution arrangement  701 . 
     Optionally, a non-specular reflector  707  may be placed over the LED lamp  700  of  FIG. 7  to capture and redirect light that might otherwise be lost. Such captured and redirected light may amount to about 30% of the light directed downwardly by light-extraction means  702 . 
     The elongated LED lamp  700  of  FIG. 7  includes electrode pins  712 . One or more power-regulating circuits  706 , shown diagrammatically, may be supported on end plates  708 . In addition, a transparent protective cover  710 , connected to end plates  708  extends along the length of the LED lamp  700 . 
     In LED light source  800  of  FIGS. 9 and 10 , LED light sources  801  transmit light  803  to associated notches  805  The LED lamp  800  includes a transparent protective cover  806 , electrode pins  807 , power-regulating circuits  809 , and end plates  808 . Light rays  803  are propagated in a sideways direction, as shown by arrows  803 , using a specular reflective surface  802 . The light-extraction means  810  can be positioned on the same side as LED light source  801 . In one example, an associated LED light source is positioned within a circumference of the light-extraction means taken about a central axis of light transmission from a respective light coupling means oriented transverse to a central path of TIR light propagation through an associated side-light distribution portion. 
     In this embodiment, the reflective surfaces  802  causes a large amount of the light emitted by the LED light sources  801  to be sent sideways in the side-light distribution arrangement  811  below the angle required for TIR propagation along the length of the arrangement  811 . Similar to LED lamp  700  of  FIGS. 6-8 , LED light source  801  may be mounted on a heat sink  804 . Specular redirection of light may be achieved by total internal reflection or the use of a reflective surface. A non-specular reflector  814  may optionally be utilized to capture and redirect light passing through light-extraction means, for instance, that otherwise could be wasted. 
       FIGS. 11 and 12  show another embodiment where the side-light distribution arrangement  901  includes protrusions  907  designed to help guide light from the LED light sources  903  to reach light-extraction means  902 . Light-extraction means can be any of those described below, under Light-Extraction Means, and could alternatively be a reflective material. Each pair of protrusions  907  extend radially outward from a side-distribution arrangement  901  with a respect to a central path of TIR light propagation through the arrangement. As used herein, a side-light distribution arrangement comprises at least three side-light distribution portions, each of which is primarily illuminated by a single LED light source. 
     The protrusions  907  could be, but are not necessarily made to closely replicate non-imaging optical coupling means such as non-imaging light-coupling means described in detail below. The protrusions  907  also provide a level of collecting and directing of the light reflected or scattered from the light-extraction means  902  in a directed manner, as indicated by arrows  905 . The protrusions  907  may run continuously along the length of the side-light distribution portion. Alternatively, the protrusions  907  may, as indicated by phantom-line areas  910  that would be absent and cause the protrusions to constitute a plurality of discrete protrusions along the length of the side-light distribution arrangement  901 . 
     In one example, the protrusions  902  extend continuously along a majority of the length of the side-light distribution arrangement  901 . In a more preferred example, the protrusions extend continuously along at least 80 percent of the length of the side-light distribution arrangement  901 . Alternatively, the protrusions can extend along the length of the side-distribution arrangement in discrete portions. 
     As shown in  FIG. 12  by light rays  905 , the light from LED light sources  903  will enter the protrusions  902 . The light-extraction means  902 , located along the top of the conical protrusion of the arrangement  901 , will direct the light back into the arrangement, creating an even illumination. 
     In  FIG. 12 , the LED light sources  903  may be mounted to metallic heat sinks  904 . Light rays  905  generated by LED light source are transmitted to the protrusions  907  and strike the light-extraction means  902 . The light rays  905  are then turned and directed out of the side-light distribution arrangement  901  because their angles now exceed the angle needed for TIR within the arrangement  901 . 
     The elongated LED lamp  900  of  FIGS. 11 and 12  include end plates  908  having power-regulating circuits  912  and electrode pins  916 . In addition, a transparent protective cover  906  is included. A non-specular reflector  914  may optionally be utilized to capture and redirect light passing through light-extraction means, for instance, that otherwise could be wasted. 
       FIGS. 13 and 14  show an alternative elongated LED lamp  1000 , wherein LED light sources  1003  are arranged as in the embodiment of  FIGS. 12 and 13 , but where the cross section of the side-light distribution arrangement  1001  is circular, as shown in  FIG. 14 .  FIGS. 15 and 16  show a similar LED lamp  1100 , but where light-extraction means  1101  is continuous along most of the length of the side-light distribution arrangement  1001 . 
     In LED lamps  1000  and  1100 , the light from light source  1003 , at least partially received within a cavity as in prior embodiments, is directed by the light-extraction means  1002  ( FIGS. 13-14 ) and  1101  ( FIGS. 15 and 16 ) out the side of the receptive side-light distribution arrangements  1001 . A non-specular reflector  1014  may be used to capture and redirect light passing through the light-extraction means  1002  or  1101 , for instance, that would otherwise be lost. 
     In  FIGS. 13 and 15 , light-extraction means  1002  or  1101  are applied over the length of the LED lamp  1000  or  1100 . The elongated LED lamps  1000  and  1100  may include specular mirrors  1005 , transparent protective covers  1008 , and end plates  1010  which includes a power-regulating circuit  1007 , similar to those described above. A reflector  1014  may be optionally be utilized, as shown in  FIG. 15 . 
     In  FIGS. 14 and 16 , LED light sources  1003  are mounted on metallic heat sinks  1004 . Light-extraction means  1101  is placed in a direction opposite to that of LED light source  1003 . A non-specular reflector  1014  may be optionally utilized. 
     The elongated LED lamp includes mirrors  1005 , end plates  1010 , a power-regulating circuit  1007  and electrode pins  1012 . 
     Non-Imaging Light Coupling Means 
     A “non-imaging” light coupling means, as used herein, tolerates minor manufacturing imperfections while retaining substantially the full functionality of an ideally formed non-imaging coupling means. 
     Normally, the light coupling means only transforms light from the light source into the proper angular distribution required by the side-light distribution arrangement. The side-light distribution arrangement normally only transports light down its length (via total internal reflection), delivering the light to the end opposite the light source. Also, the light-extraction means only extracts light transverse to the length of the side-light distribution arrangement; it does not collect light from a light source or perform any angular transformation of the light. 
     Regarding the light coupling means, its interiorly-directed reflective surface is normally the primary device for receiving light from a light source. It then transmits that light toward a light-receiving portion of a side-light distribution arrangement, which is discussed in later paragraphs. This reflective surface is typically specular if the light coupling means is hollow, or of the TIR-type if the light coupling means is solid, where TIR means total internal reflection. 
     The rules of non-imaging optics govern the configuration of the light coupling means at least approximately. As known in the art, the rules of non-imaging optics are concerned with the optimal transfer of light radiation between a source and a target. In contrast to traditional imaging optics, non-imaging techniques do not attempt to form an image of the source; instead, an optimized optical system for radiative transfer from a source to a target is desired. 
     The two design problems that non-imaging optics solves better than imaging optics are as follows, First, (1) concentration—maximizing the amount of energy applied to the target (as in solar power, for instance, “collecting radiation emitted by high-energy particle collisions using the fewest number of photomultiplier tubes”). Second, (2) illumination—controlling the distribution of light, typically so it is “evenly” spread over some areas and completely blocked from other areas (as in automotive headlamps, LCD backlights, etc.). 
     Typical variables to be optimized at the target include the total radiant flux, the angular distribution of optical radiation, and the spatial distribution of optical radiation. These variables on the target side of the optical system often must be optimized while simultaneously considering the collection efficiency of the optical system at the source. 
     Typically, a light coupling means at least approximately governed by the rules of non-imaging optics has a profile that changes from the inlet end toward the outlet end to condition the angular distribution of light provided to a rod-shaped side-light distribution arrangement. That is, as light propagates through the light coupling means, its angular distribution changes. In addition, the interior surface of a solid light coupling means may be configured to aid in the conditioning of light provided to a rod-shaped light pipe. 
     This change in the angular distribution of light conditions the light for distribution by the side-light distribution arrangement. Three examples are as follows. First, (1) the light may be conditioned to reduce the angular distribution of light to be significantly below the numerical aperture or acceptance angle of a side-light distribution arrangement so that it propagates along the entire length of the side-light distribution arrangement and is distributed out the opposite end. 
     In a second example (2), the angular distribution of light leaving the light coupling means can be higher but closer, or even beyond, the numerical aperture (NA) of the side-light distribution arrangement. In this case, the light leaving the light coupling means with a higher angular distribution will see a greater number of interactions with the sides of the side-light distribution arrangement, thereby increasing the opportunity for distribution out the side of the side-light distribution arrangement over a shorter distance. 
     In a third example (3), the profile of the light coupling means changes so that the light leaving the light coupling means is not only conditioned to cause the angular distribution to be within an intended NA, but also is conditioned to cause the light to be uniformly distributed among a greater number of angles. In this case, at least approximately governed by the rules of non-imaging optics, the profile of the light coupling means will typically grow in size and then decrease as it approaches and reaches the side-light distribution arrangement. Because the resulting light is conditioned so that light is present at a multitude of angles, light with higher angles will have more interactions with the side of the side-light distribution arrangement and will be distributed over shorter distances, and light with lower angles will see fewer interactions so will be distributed over longer distances. The result may be a more uniform distribution out of the side-light distribution arrangement along its entirety. 
     With respect to the light coupling means, the coupling means can have an increasing cross-sectional area from a light coupling inlet end and a light coupling outlet end. The change in area for the light coupling means can be of a non-monotonic function, for example, a compound parabolic curve. The increase in cross-sectional area of the light coupler may follow the pattern disclosed in U.S. Pat. No. 6,219,480, the disclosure of which is incorporated herein by reference. More specifically, the cross-sectional area of the light coupling means increases in a continuous manner, where “continuous” means that the cross section at a point along an axial length transitions to a next point without any substantial discontinuities. 
     Alternatively, the cross-sectional area of the light coupling means can increase and decrease in a continuous manner, where “continuous” means that the cross section at a point along an axial length transitions to a next point without any substantial discontinuities. 
     In another example, the cross-sectional area of the light coupling means increases or decreases in a continuous manner, where “continuous” means that the cross section at a point along an axial length transitions to a next point without any substantial discontinuities. For example, a central path of light propagation occurs from an inlet end to an outlet end, where a cross-section increases from a first cross-sectional area to a maximum cross-sectional area and then decreases in cross-section to a final cross-sectional area larger than the first cross-sectional area. 
     Side-Light Distribution Arrangement 
     A side-light distribution arrangement as used herein preferably comprises an elongated rod. By “elongated” it is meant being long in relation to width or diameter, for instance, where the “long” dimension can be both along a straight path or a curved path. 
     One end of the side-light distribution arrangement receives light from an associated light coupling means. The elongated rod has an elongated sidewall and light-extraction means along at least part of the elongated sidewall for extracting light through the sidewall and distributing said light to a target area. At least, the part of the side-light distribution arrangement having light-extraction means is preferably solid, although there may exist in the arrangement small voids caused by manufacturing processes, for instance, voids that have insubstantial impact on the side-light light-extraction and distribution properties of the side-light distribution arrangement. 
     A side-light distribution arrangement as used herein has a cross section along a main axis of light propagation through the pipe that is more round than flat. For example, the minimum cross-sectional dimension is preferably more than 50% of the maximum cross-sectional dimension. In a preferred embodiment, the cross-section of the side-light distribution arrangement is substantially circular. 
     Preferably, a side-light distribution arrangement is rigid, by which is meant that at 20 degrees Celsius the arrangement has a self-supporting shape such that the light pipe returns to its original or approximately original (e.g., linear or curved) shape after being bent along a main path of light propagation through the light pipe. However, if the side-light distribution arrangement is flexible, it is meant that the side-light distribution arrangement has a shape that will be bent to a shape that has a curvature when being bent along its longitudinal axis. 
     The preferred embodiment of the side-light distribution arrangement is one that includes a constant cross-sectional area, within manufacturing tolerances known to a person of ordinary skill. Such constant cross-sectional area is within a + or −5% deviation. In one example, a useful embodiment of the system may include a monotonically increasing cross-sectional area of the side-light distribution arrangement. The increasing cross-sectional area reduces the angular distribution of light passing through the light coupling means, so as to enable the light rays to propagate at higher angles while maintaining total internal reflection. 
     The decreasing cross-sectional area aids in extraction of light from the sides of the side-light distribution arrangement, because the angles of light effectively become steeper with respect to the covering surface of the side-light distribution arrangement. 
     The side-light distribution arrangement may have a nearly constant cross-sectional area. The term “nearly constant” cross-sectional area indicates a generally constant cross-sectional area with + or −5% deviation. The cross-sectional area of the side-light distribution arrangement may become “gradually larger” starting from the inlet end and moving towards the second end of the side-light distribution arrangement. Alternatively, the cross-sectional area of the side-light distribution arrangement may become “gradually smaller” starting from the inlet end and moving towards the second end of the side-light distribution arrangement. When defining “gradually larger” or “gradually smaller,” the cross-sectional area increases or decreases in a continuous manner, where “continuous” means that the cross section at a point along an axial length transitions to a next point without any substantial discontinuities, as disclosed in the foregoing &#39;480 patent. The change in cross-sectional area is of a monotonic function. 
     Light-Extraction Means 
     Now specific examples of the light-extraction means will be discussed. Light-extraction means may be of various types whose selection will be routine to those of ordinary skill in the art. For instance, three types of light-scattering means are disclosed in U.S. Pat. No. 7,163,326, entitled “Efficient Side-light Luminaire with Directional Side-Light-Extraction,” assigned to Energy Focus, Inc. of Solon, Ohio. In brief, these three types are (1) discontinuities on the surface of a side-light distribution arrangement, (2) a layer of paint on the surface of a side-light distribution arrangement, and (3) a vinyl sticker applied to the surface of a side-light distribution arrangement. 
     In more detail, (1) discontinuities on the surface of a side-light distribution arrangement may be formed, for instance, by creating a textured pattern on the side-light distribution arrangement surface by molding, by roughening the side-light distribution arrangement surface with chemical etchant, or by making one or more notches in the side of a side-light distribution arrangement. 
     In another example, the light-extraction means may comprise a layer of paint exhibiting Lambertian-scattering and having a binder with a refractive index about the same as, or greater than that of, the core. Suitable light-extraction particles are added to the paint, such as titanium dioxide or many other materials as will be apparent to those of ordinary skill in the art. Preferably, the paint is an organic solvent-based paint. 
     In yet another example, the light-extraction means may comprise vinyl sticker material in a desired shape applied to the surface of the side-light distribution arrangement. Appropriate vinyl stickers have been supplied by Avery Graphics, a division of Avery Dennison of Pasadena, Calif. The film is an adhesive white vinyl film of 0.146 mm, typically used for backlit signs. 
     In another example, the light-extraction means may be continuous, intermittent, or both, along the length of a side-light distribution arrangement, for instance. An intermittent pattern is shown in the above-mentioned U.S. Pat. No. 7,163,326 in  FIG. 15A , for instance. To assure that the light-extraction means appears as continuous from the point of view of the observer in a target area to be illuminated, the target area should be spaced from the side-light distribution arrangement in the following manner: the spacing should be at least five times the length of the largest gaps between adjacent portions of paint or other light-extraction means along the main path of TIR light propagation through the side-light distribution arrangement. 
     Additionally, the foregoing light-extraction patterns may be of the specular type, scattering type, or a combination of both. Generally, a scattering extractor pattern for light on an elongated side-light distribution arrangement tends to provide light onto a target area, along the length of the side-light distribution arrangement, with a moderate degree of directional control over the light in the length direction. In the direction orthogonal to the length, the scattering extractor pattern density and the cross sectional shape of the elongated side-light distribution arrangement provide a smooth target distribution that is free of localized spatial structure but still provides good directional control. Scattering extractor patterns are relatively insensitive to fabrication errors. 
     In contrast, as used herein, a specular extraction pattern can provide light along the length of a side-light distribution arrangement with more localized control than can a scattering extraction pattern. 
     The following is a list of reference numerals and associated parts as used in this specification and drawings: 
     
       
         
           
               
               
             
               
                   
               
               
                 Reference Numeral 
                 Part 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 200 
                 LED lamp 
               
               
                 201 
                 Electrode Pins 
               
               
                 202 
                 Sleeve 
               
               
                 204 
                 LED light source 
               
               
                 205 
                 Heat sink 
               
               
                 300 
                 LED lamp 
               
               
                 302 
                 Electrode Pins 
               
               
                 304 
                 End plates 
               
               
                 306 
                 Protective sleeve 
               
               
                 308 
                 Support 
               
               
                 310 
                 Light-extraction means 
               
               
                 311 
                 Light coupling means 
               
               
                 312 
                 Bracket 
               
               
                 314 
                 Side-light distribution portion 
               
               
                 318 
                 LED light source 
               
               
                 320 
                 Heat sink 
               
               
                 400 
                 LED lamp 
               
               
                 600 
                 LED lamp 
               
               
                 601 
                 LED light source 
               
               
                 602 
                 Light coupling means 
               
               
                 603 
                 Heat sink 
               
               
                 604 
                 Connecting portion 
               
               
                 605 
                 Light-extraction means 
               
               
                 606 
                 Power-Regulating Circuit 
               
               
                 607 
                 Mirror 
               
               
                 608 
                 Support Structure 
               
               
                 609 
                 Side-light distribution portion 
               
               
                 610 
                 Side-light distribution arrangement 
               
               
                 611 
                 Electrode pins 
               
               
                 612 
                 Protective cover 
               
               
                 700 
                 LED lamp 
               
               
                 701 
                 Side-light distribution arrangement 
               
               
                 702 
                 Light-extraction means 
               
               
                 703 
                 LED light source 
               
               
                 704 
                 Heat sink 
               
               
                 705 
                 Light rays 
               
               
                 706 
                 Power-regulating Circuit 
               
               
                 707 
                 Reflector 
               
               
                 708 
                 End plate 
               
               
                 710 
                 Protective cover 
               
               
                 712 
                 Electrode Pins 
               
               
                 800 
                 LED lamp 
               
               
                 801 
                 LED light source 
               
               
                 802 
                 Reflective surface 
               
               
                 803 
                 Light ray 
               
               
                 804 
                 Heat sink 
               
               
                 805 
                 Notches 
               
               
                 806 
                 Protective cover 
               
               
                 807 
                 Electrode Pins 
               
               
                 808 
                 End Pins 
               
               
                 809 
                 Power-regulating Circuit 
               
               
                 810 
                 Light-extraction means 
               
               
                 811 
                 Side-light distribution arrangement 
               
               
                 814 
                 Reflector 
               
               
                 900 
                 LED lamp 
               
               
                 901 
                 Side-light distribution arrangement 
               
               
                 902 
                 Light-extraction means 
               
               
                 903 
                 LED light source 
               
               
                 904 
                 Heat sink 
               
               
                 905 
                 Light ray 
               
               
                 906 
                 Protective cover 
               
               
                 907 
                 Protrusions 
               
               
                 908 
                 End plate 
               
               
                 910 
                 Phantom-line area 
               
               
                 912 
                 Power-regulating Circuit 
               
               
                 916 
                 Electrode Pins 
               
               
                 1000 
                 LED lamp 
               
               
                 1001 
                 Side-light distribution arrangement 
               
               
                 1002 
                 Light-extraction means 
               
               
                 1003 
                 LED light source 
               
               
                 1004 
                 Heat sink 
               
               
                 1005 
                 Mirror 
               
               
                 1006 
                 Protective cover 
               
               
                 1007 
                 Power-regulating circuit 
               
               
                 1008 
                 Protective cover 
               
               
                 1010 
                 Power-regulating Circuit 
               
               
                 1012 
                 Electrode Pins 
               
               
                 1100 
                 LED lamp 
               
               
                 1101 
                 Light-extraction means 
               
               
                   
               
            
           
         
       
     
     While the principles of the invention have been described herein, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation as to the scope of the invention. Other embodiments are contemplated within the scope of the present invention in addition to the exemplary embodiments shown and described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the following claims.