Patent Publication Number: US-7222995-B1

Title: Unitary reflector and lens combination for a light emitting device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates portable lighting apparatus and, more particularly, to optical, mechanical, and electrical features for the design, utility, and performance of portable task lighting and flash light apparatus using very small light emitting devices. 
     2. Description of the Prior Art 
     Lighting devices can be grouped into two basic applications: illumination devices and signaling devices. Illumination devices enable one to see into darkened areas. Signaling devices are designed to be seen, to convey information, in both darkened and well-lit areas. Widely available varieties of portable lighting apparatus, which may combine both the illumination type and the signaling type, employ a variety of lighting technologies in products such as task lamps and flashlights. Each new development in technology is followed by products that attempt to take advantage of the technology to improve performance or provide a lower cost product. For example, incandescent bulb technology in small and/or portable lighting products is being challenged by compact fluorescent lamp (CFL) bulbs, often in association with electronic ballast circuits. Other types of incandescent bulbs such as halogen lamps have become standard in a number of ordinary applications. High intensity discharge (HID) and other arc lighting technologies are finding ready markets in automotive and high brightness flood lighting, spot lighting, and signaling applications. 
     More recently, solid state or semiconductor devices such as light emitting diodes are finding use as compact and efficient light sources in a wide variety of applications. These applications include high intensity personal lighting, traffic and other types of signal lighting, automotive tail lamps, bicycle lighting, task lighting, flashlights, etc., to name a few examples. This technology is relatively new, however, and conventional products heretofore have suffered from a number of deficiencies. For example, current products utilizing light emitting diodes as light sources tend to be highly specialized and suited to only a single use, thus limiting their versatility as lighting devices or instruments for more ordinary uses. Further, such specialized devices tend to be expensive because of the relatively low production volumes associated with specialized applications. 
     Moreover, there exist certain lighting applications for which conventional light sources are unsatisfactory because of limitations in brightness, operating life, durability, power requirements, excessive physical size, poor energy efficiency, and the like. Newer light sources such as semiconductor light emitting diodes are very small, very durable, use relatively little power, have long lifetimes, and emit very bright light relative to the electrical power input. While some presently available products employ these semiconductor light sources, their full potential is frequently not realized. This may occur because of deficiencies in optical components and drive circuits, or interface components having particular combinations of structure and function are not available. Another factor may be that improvements in the design and configuration of multiple, small, high intensity light sources for maximum illumination efficiency and convenience of use have not been forthcoming. 
     An advance in the state of the art could be realized if such small, high intensity and high efficiency light emitting devices could be adapted to more general and more versatile lighting applications such as flood lighting or spot lighting. Such advances could occur if improvements in the components, circuits, and product architecture are developed and provided. 
     For example, in the field of lighting devices used by security personnel, there is a need for high intensity illumination in a battery powered, hand-held instrument that is very rugged, efficient in the use of power, and that provides a beam of light designed to illuminate dark regions of or indistinct objects within an area being patrolled or investigated. Many circumstances require a bright, well-shaped flood light beam for illuminating relatively large areas. Other situations require a more directed beam of light, to spotlight particular areas or objects. Ideally, both modes of illumination would be combined in a single instrument. 
     SUMMARY OF THE INVENTION 
     Accordingly, in one aspect of the present invention, there is provided a combination task lamp and flash light, comprising first and second elongated shells forming an elongated, tubular housing having a longitudinal axis, a first section at a first end for containing a plurality of light emitting device (LED) light sources and a second section at a second end for containing a power supply; the first section of the combination including a first directed array of LED/lens assemblies for providing flood light illumination and a second directed light array of at least one LED/lens assembly for providing spot light illumination. 
     In another aspect of the invention, there is provided a lens for a light emitting device (LED) comprising a combination of an aspherical reflecting surface and a spherical refracting surface. The aspherical reflecting surface has a focal point and a central axis of symmetry—i.e., an optical axis—for reflecting light rays emitted from a compact light source located approximately at the focal point in a forward direction and the reflected light rays are emitted approximately within a predetermined angle with respect to the optical axis. The spherical refracting surface is disposed in the path of the reflected light rays, centered on and normal to the central axis, concave in the forward direction of the reflected light rays and joins the aspherical reflecting surface at a boundary equidistant from the optical axis. The spherical refracting surface includes a plurality of N concentric annular surfaces, each annular surface having a cross section convex in the forward direction and disposed substantially at uniform radial intervals between the optical axis and the junction with the aspherical reflecting surface. 
     In another aspect of the present invention, there is provided a circuit for illuminating multiple light emitting devices, comprising a current selector circuit connected across a positive terminal and a negative terminal of a DC supply for selecting operating current from the DC supply to each of a first array and a second array of the multiple light emitting devices (LEDs); a switching regulator circuit connected across an output of the current selector circuit for respectively regulating first and second constant drive currents to the first array of LEDs and to the second array of LEDs; a first array of LEDs coupled between a first output of the switching regulator circuit and a common current sense device; and a second array of LEDs coupled between the first output of the switching regulator circuit and the common current sense device; wherein a voltage signal generated by the common current sense device is coupled to a sense input of the switching regulator circuit for regulating the constant drive currents supplied to the first and second arrays of LEDs. 
     In another aspect of the invention, there is provided a light emitting module comprising a frame configured as a heat sink having first and second opposite sides and a forward axis normal to the first side thereof. Each one of an array of a plurality N of light emitting assemblies (LEAs) connected to a source of current is mounted on the first side of the frame configured as a heat sink such that the central axis of light emission of each LEA is disposed at a non-zero first predetermined angle relative to the forward axis. The frame may include a printed circuit embodying an electric circuit coupled to the array of light emitting assemblies. 
     In yet another aspect of the present invention, there is provided an electric circuit comprising an electric circuit having an output and a single pole, single throw (SPST) switch having normally open (NO) first and second contacts and a latching mechanism operable by an actuating member. The switch is connected in the electric circuit for activating at least a conducting path in the electric circuit wherein the switch is sequentially operable in first, second, and third states corresponding respectively to latched engagement, momentary disengagement, and latched disengagement of the first and second contacts in the switch. The first state provides activation of the electric circuit in an OFF condition, the second state provides momentary activation of the electric circuit in an ON condition, and the third state provides latched activation of the electric circuit in an ON condition. 
     In yet another aspect of the present invention, there is provided a method of operating a single pole, single throw (SPST) switch in three distinct states in an electric circuit. The method comprises the steps of providing in an electric circuit having at least an output a SPST normally open (NO) switch for activating at least a conducting path in the electric circuit, the switch having first and second contacts and a latching mechanism operated by an actuating member; providing a first state wherein the latching mechanism is activated, the first and second contacts are engaged, and the electric circuit is in an OFF condition; providing a second, momentary state by exerting a first force upon the actuating member of the SPST switch, sufficient to disengage but not latch the first and second contacts, thereby causing the electric circuit to enter a temporary ON condition during the second state, wherein release of the first force upon the actuating member causes restoration of the first state; and providing a third state by exerting a second force greater than the first force upon the actuating member of the SPST switch, wherein the latching mechanism is activated and the first and second contacts are disengaged, causing the electric circuit to remain in an ON condition. A repeated exertion of the second force upon the actuating member of the SPST switch causes engagement of the first and second contacts, causing in turn the electric circuit to enter the OFF condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and other objects of the invention disclosed herein will be understood from the following detailed description read with reference to the accompanying drawings of one embodiment of the invention. Structures appearing in more than one figure and bearing the same reference number are to be construed as the same structure. 
         FIG. 1  illustrates one embodiment of a perspective view of a combination task lamp and flash light according to the present invention that provides both flood and spot light illumination; 
         FIG. 2  illustrates a perspective view of the embodiment of  FIG. 1  showing a preferred configuration of light emitting assemblies and the directionality of their respective emissions of light; 
         FIG. 3  illustrates a plan view of a flood light pattern on a flat target surface at a nominal distance from the embodiment of  FIG. 1 , showing the overlapping of beams of light from individual emitters; 
         FIG. 4A  illustrates a cross section profile of a solid body lens for use with each light emitting device in the embodiment of  FIG. 1 ; 
         FIG. 4B  illustrates an enlarged cross section of a portion of  FIG. 4A  to show detail thereof; 
         FIG. 4C  illustrates a cross section profile of the solid body lens of  FIG. 4A  in assembly with a light emitting device assembly; 
         FIG. 5  illustrates a block diagram of an electrical circuit for use in the embodiment of  FIG. 1  for powering and controlling the light outputs thereof; 
         FIG. 6A  illustrates a first portion of a schematic diagram of the electrical circuit of  FIG. 5 ; 
         FIG. 6B  illustrates a second portion of the schematic diagram of the electrical circuit of  FIG. 5 ; 
         FIG. 7  illustrates an exploded view of major parts and assemblies of the embodiment of  FIG. 1 ; 
         FIG. 8A  illustrates a perspective view of a rearward side of a light emitting module of the embodiment of  FIG. 1 ; 
         FIG. 8B  illustrates a perspective view of the forward side of the light emitting module illustrated in  FIG. 8A ; 
         FIG. 8C  illustrates a perspective view of a basic module portion of the light emitting module appearing in  FIG. 8B ; and 
         FIG. 8D  illustrates a side cross section view of the light emitting module of the embodiment of  FIGS. 8A and 8B . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , there is illustrated one embodiment of a perspective view of a portable, combination task lamp and flash light (also referred to herein as a portable lighting device  10  or “PLD  10 ,” that provides both flood and spot light illumination, and is constructed according to the present invention. The PLD  10  includes an elongated tubular housing  12  defined along a longitudinal axis  14 , having a first section  16  at a first end for containing a plurality of light emitting assemblies or light sources  22 , and further having a second section  18  at a second end for containing a power supply (See  FIG. 7 ). Visible through a clear side lens  24  in  FIG. 1  is a bezel  20  that locates the forward surfaces of four light sources  22  substantially in a row. The side lens  24  is an internal component of the housing  12  as will be further described with  FIG. 7 . The row of four light sources  22  may be denoted as a first directed array of light sources  22 . Any number of individual light sources  22  may be arranged in a variety of configurations to form a directed array. In the present illustrative embodiment, the configuration of four light sources  22  disposed in a row is selected to illustrate the principles of the invention in a specific product application. 
     In general, each of the light sources  22  may be a combination of a light emitting device (LED) and a lens assembly. The combination of an LED and a lens assembly may further be denoted as a light emitting assembly (LEA) or as a lens/LED assembly. An LED may be a semiconductor light emitting diode or it may be a light emitting device employing a different technology to produce light. A lens assembly may be a single, solid body of optical material having one or more predetermined optically responsive surface configurations or it may be constructed as a combination of separate, predetermined optical elements assembled into a single unit. In the illustrated embodiment, the lens is a solid body element having a plurality of predetermined surface configurations that is designed for use with certain types of light emitting diodes. 
     Continuing with  FIG. 1 , a clear top lens  28  of a second directed light array  26  is disposed in the end of the first section  16  of the elongated housing  12 . Although the clear top lens  28  indicates that a single light source is shown in the illustrative embodiment, it is possible that several individual light sources may be used to construct the second directed light array  26 . The second directed light array  26  visible through the clear top lens  28  may be configured as a spot light beam or as a flood light beam. Typically, with a PLD  10  having a first directed light array  22  configured to provide a flood light beam, the second directed light array  26  may be advantageously configured as a spot light beam. As will become apparent, when using very small or compact light sources, the type of light beam provided is largely dependent upon the lens assembly provided for the light source. Generally, the light source for the second directed light array  26  may be aligned such that its optical axis is coincident with or aligned parallel with the longitudinal axis  14 . In other applications, the alignment of the second directed array  26  may be disposed at an angle (fixed or adjustable) relative to the longitudinal axis. In such cases, the optical axis of the second directed light array  26  would be aligned at a non-zero angle with respect to the longitudinal axis. 
     At the end of the first section  16  of the elongated housing  12  a lens frame  30  disposed over the second directed light array of lens  26  is provided to protect the clear top lens  28 . The lens frame  30  may be formed as part of the elongated housing  12  or implemented as a separate component. It will be observed that the lens frame  30  has a three-sided, tubular shape, i.e., a substantially triangular shape wherein the three sides bulge slightly outward as with a convex surface. This triangular shape mimics the shape of the cross section of the elongated housing  12  in the first section  16 . In the illustrated embodiment, the triangular cross section of the first section  16  may be configured to merge with a substantially round or oval cross section of the second section  18 . The triangular shape is provided so that when the PLD  10  is placed on a horizontal surface, the PLD  10  naturally assumes an orientation so that the flood light beam from the first directed light array is projected upward at an angle from the horizontal. This is a useful feature when both hands must be free to work. 
     At the opposite end of the elongated housing  12 , the second section  18  may be configured to contain a power supply such as a battery pack. The external portions of the second section  18  may be formed as a handle or with other features to provide a comfortable or a non-slippery gripping surface. A removable end cap  32  may be provided for access to the interior of the second section  18  of the elongated housing  12  such as to replace a battery. In other applications the cap  32  may include a connector for a line cord (not shown in  FIG. 1 ) to supply external power to a power supply converter or battery charger contained within the second section  18 , for example. 
     Referring to  FIG. 2 , there is illustrated a perspective view of the embodiment of  FIG. 1  showing a preferred configuration of light emitting assemblies and the directionality of their respective emissions of light. As will be described further with  FIGS. 4A ,  4 B, and  4 C infra, each of the light sources  22  is an assembly of a light emitting assembly (including a light emitter or light emitting device) and a lens assembly. In  FIG. 2 , each of the light sources  22  is shown aligned with respect to an associated light emitter (designated as E 1 , E 2 , E 3 , and E 4 ) along an optical axis thereof. The light emitting assembly including the light emitter and the lens assembly share the same optical axis. In the example illustrated in  FIG. 2 , the optical axis (designated by a dashed line) of the light emitter of each light source  22  is disposed at an angle θ with respect to a normal reference line (designated as N 1 , N 2 , N 3 , and N 4 ) at the location of each light source  22 . It is known to persons skilled in the art that a “normal” reference line is oriented perpendicular to a plane surface, in this case to the plane surface  48  on which the focal point of the individual light emitter is located. The angle θ will be described in further detail herein below. 
     Each of the light emitters E 1 , E 2 , E 3 , and E 4  are shown mounted on the plane surface  48  in the interior of the elongated housing  12 . The light sources  22 , associated with each of the light emitters are not fully illustrated so that the relationship of the light emitters E 1 , E 2 , E 3 , and E 4  and the elongated housing  12  may be more clearly illustrated. In the illustrated embodiment, a light emitter may be a light emitting diode having an active element (See also  FIG. 4C ) mounted inside a hemispherical dome  40  on a base  42 . The base  42  may be attached to a substrate  44 , such as a printed circuit board. The substrate  44  may be a laminated structure that includes a bottom layer (not shown) of thermally conductive material such as aluminum. The aluminum layer provides an integral heat sink for the light source emitter assembly for low power applications and a suitable conductive bonding surface for higher power applications where more heat must be dissipated via an external heat sink in contact with the substrate  44 . In the illustrated example, the plane surface  48  is preferably configured as such external heat sink for conducting heat away from the light emitting assembly and dissipating it into the surroundings. A thermal compound of the type well known in the art may be placed in the interface between the substrate  44  and the plane surface  48 . 
     As described previously, an optical axis is defined for each of the light sources  22 . In the illustrated embodiment, the optical axes are defined at an angle θ with respect to the normal line defined for each of the light sources  22 . The same angle θ is used in this particular embodiment for all four of the light emitting assemblies for reasons which will be described. Thus, the optical axis  52  for the E1 emitter is shown by the dashed line labeled “E1 Axis” and bearing reference number  52 . Optical axis  52  is defined to be oriented vertically upward relative to the normal line  62  (N 1 ), from the perspective of the PLD  10 , at the angle indicated by the symbol θ. Similarly, optical axis  54  (the E2 axis) is defined to be oriented horizontally leftward relative to the normal line  64  (N 2 ), from the perspective of the PLD  10 , at the angle indicated by the symbol θ. Similarly, optical axis  56  (the E3 axis) is defined to be oriented horizontally rightward relative to the normal line  66  (N 3 ), from the perspective of the PLD  10 , at the angle indicated by the symbol θ. Likewise, optical axis  58  (the E4 axis) is defined to be oriented vertically downward relative to the normal line  68  (N 4 ), from the perspective of the PLD  10 , at the angle indicated by the symbol θ. Thus, each of the light sources  22  is oriented or aimed at the angle θ relative to a normal reference line perpendicular to the plane surface  48  at the location of the particular light source  22 . 
     Moreover, in an array of N light emitting assemblies supported on a common planar base having a normal forward axis, the individual optical axes of the light emitting assemblies will be disposed such that they diverge from a reference line parallel to the forward axis by the angle θ. Further, the individual planes containing the reference line and the optical axis of each light emitting assembly are disposed at substantially equal angles from each other, in the manner of spokes of a wheel when viewed from a point on the forward axis looking back toward the origin of the forward axis. This arrangement of the optical axes of the individual light emitting assemblies is shown in  FIG. 2  for an array of N=4 emitters arranged in a straight line on a flat common planar base. As will be described, the orientation of the optical axes of this array at the angle θ of approximately 5 degrees (5°), wherein each light emitting assembly provides a beam of light having a beam width angle of approximately 40 degrees (40°), a composite beam pattern of high brightness and uniformity of cross section is provided. 
     It should be appreciated that the optical axes of opposing pairs of light emitting assemblies in such an array diverge by twice the angle θ, which in the illustrated embodiment is 2×5°=10°. During the development of the present invention, it was discovered that the relationship between the amount of divergence between two light emitting assemblies in an array (here 10°) and the beam width angle of the individual light emitting assemblies in the array (here 40°) turns out to be an optimum relationship for producing a high brightness, high uniformity composite beam cross section. The relationship may be stated as the ratio of the divergence angle to the beam width angle. In this example it is one to four, or a “one quarter beam width” index or figure of merit. Thus, for a given beam width from a light emitting assembly having a substantially point source light emitter and a lens assembly configured to produce the given beam width, the optimum amount of divergence between two such light emitting assemblies or pairs of such light emitting assemblies turns out to be one quarter of the beam width of the individual light emitting assemblies. This index is very useful in devising arrays of light emitting assemblies to provide a particular composite beam of light or illumination pattern from the array, as will become more apparent in the detailed description which follows. 
     Continuing with the description of  FIG. 2 , when the plane surface  48  is a flat surface, all four of the normal lines at each of the light source positions are parallel to each other. In the illustrated embodiment, the light sources are disposed in a row because of the space limitations of the elongated tubular housing  12 . However, in an embodiment that allowed the four light sources to be clustered close together on a flat plane surface in a rectangular array, for example at the four corners of a square, the normal lines may be closer together and, in fact, a single normal line placed at the center of the array could serve as the reference for all four of the light sources. In such an embodiment, the light sources would still be advantageously oriented with their optical axes diverging from the common normal line by the angle θ. Further, each of the four light sources would also be divergent in a direction that is at right angles from the direction of divergence of each of its neighboring light source. Thus, the optical axes—and the respective light beams—of the four light sources are aimed in a manner that mimics the four compass directions N, W, S, and E, or, the four spokes of a wheel wherein the spokes are 90° apart. 
     The same aiming arrangement is provided in the illustrated embodiment of  FIG. 2 , where the four light sources  22  are arranged in a row. That is, the optical axes of the light sources  22  diverge in the compass directions N, W, S, and E, when viewed from the position of the longitudinal axis  14 , even though the light sources  22  are arranged in a single row and are somewhat more widely spaced. In either of the described embodiments, as illustrated in  FIG. 2  or in the preceding paragraph, from the perspective of the PLD  10 , the beam from light source E 1  diverges northward, E 2  diverges westward, E 3  diverges southward, and E 4  diverges eastward. Thus, the respective beam cross sections, as the composite beam is projected on a flat wall surface, will include some overlap. This characteristic will be shown in  FIG. 3  to be described. 
     In the illustrative embodiment, the angle θ is a non-zero angle typically less than approximately ten degrees (10°). In the preferred embodiment, θ is approximately 5°. This amount of divergence provides an enhanced flood light pattern when projected on a plane surface at a distance of three to four meters, as shown in  FIG. 3 , to be described. Experimentation has shown that the angle θ is dependent on the design of the lens assembly, particularly the factors of the lens assembly that affect the angle β of the beam width. The beam width angle β is the angle between the sides of a cone that defines the locus of the light rays emitted from a light source located at the apex of the cone. Further, as described herein above, the beam width angle β, the optical axis divergence angle θ, and the properties and positions of the aspherical surfaces of the lens assembly may be adjusted according to the one quarter beam width index to produce the brightest, most uniform flood light pattern at a distance of three to four meters in the illustrative embodiment. The relationships of these parameters will become clearer in the description which follows. 
     In some embodiments, the plane surface  48  shown in  FIG. 2  may be curved to provide a particular orientation of the light emitting assemblies mounted thereon. Thus, with the focal points of the light emitting assemblies coincident with the plane surface  48 , bending the plane surface to provide a predetermined curvorients the optical axes of the individual light emitting assemblies to conform to other beam configurations. In such cases the forward axes may be defined at the location of each of the light emitting assemblies. Further, the optical axes of the individual light emitting assemblies may be oriented at non-zero or zero angles with respect to the reference forward axis at a particular location on the plane surface  48 . In yet other embodiments the curvature or departure from flat of the plane surface  48  may be adjustable, either in production or by the user, to produce several beam outputs adapted to different applications. In the example described above, bending the plane surface  48  is by way of illustration and not intended to limit the choice of design or method available to the designer. Other design configurations may of course be implemented to configure the mounting surface for the light emitting assemblies with the desired curvature. 
     Referring to  FIG. 3 , there is illustrated a plan view of an overall flood light pattern projected on a flat target surface at a nominal distance from the embodiment of  FIG. 1 , showing the overlapping of beams of light from individual emitters to form a composite beam  80 .  FIG. 3  will be best understood when viewed in combination with  FIG. 2 . Each of the regions identified in  FIG. 3  are distinguished by the relative amount of shading applied to the various regions. Thus, light emitter E 1  having an optical axis  52  provides a projected beam cross section or pattern  82 . Similarly, light emitter E 2  having an optical axis  54  provides a projected beam cross section or pattern  84 . Similarly, light emitter E 3  having an optical axis  56  provides a projected beam cross section or pattern  86 . Likewise, light emitter E 4  having an optical axis  58  provides a projected beam cross section or pattern  88 . 
     Continuing with  FIG. 3 , the result of combining the respective patterns  82 ,  84 ,  86 , and  88  produces the overlap region  90  in the center portion of the composite beam  80 , where all four of the beams overlap. In this central region  90 , the pattern resembles a square with rounded sides that bulge outward, roughly approximating a round region. Three of the beam cross sections from light emitters overlap in the four regions identified with the reference number  92 . Two of the beam cross sections from light emitters overlap in the four regions identified with the reference number  94 . The four regions identified with the reference number  96  results from the light emitted by a single light emitter. One characteristic about the composite beam pattern  80  produced by all four light beams is that it is approximately round and provides a brightness that is substantially uniform at all angles around the center of the pattern and varies uniformly with distance from the center. Such a pattern balances the light outputs to maximize the utility in a flood lighting application. 
     The degree of overlap in the projected composite beam pattern  80  of  FIG. 3  may be adjusted by variations in the angle of the respective optical axes of the individual light emitters. For lighting instruments intended for illumination at certain distances or within a specified range of distances, the optical axis angles of the light emitters may be adjusted accordingly. In the preferred embodiment illustrated and described herein, the angle of the optical axes relative to the reference normal is approximately 5° to provide the pattern illustrated in  FIG. 3  on a target approximately 3 to 4 meters away. In the illustrated embodiment, the optical axes are disposed at a fixed angle because the individual light emitters are mounted on a single heat dissipating frame (heat sink) to be described in detail herein below with  FIG. 8C . In other embodiments the angles of the optical axes may be configured to be adjustable to increase the versatility of the PLD  10 . Further, the symmetry of the overall pattern is readily apparent in  FIG. 3 ; however, the symmetry is dependent on the uniformity of the alignment of the respective optical axes as will be appreciated by those skilled in the art. 
     Referring to  FIG. 4A , there is illustrated a cross section profile of a solid body lens assembly  100  for use with each light emitting device of the first directed array of LEDs  22  in the embodiment of  FIG. 1 . The lens assembly  100  may be molded or cast from a clear, optical grade material having an index of refraction n within the range n=√2 to 2.00, and preferably within the range of n=1.45 to 1.60. Thermoplastic materials such as polycarbonate (PC), polymerized methyl methacrylate (PMMA, or “acrylic”), or polyethylene terephthalate (PET) are generally suitable. In the preferred embodiment, polycarbonate (PC) is selected for its stability within the temperature range of −60° F. to +270° F., as compared to acrylic having an upper temperature limit of approximately 160° F. (PMMA Grade 8). While both PC and acrylic have a refractive index n=1.49, acrylic has slightly better light transmission (92% vs. 89%) and better resistance to ultraviolet (uv) radiation, the higher temperature limit of PC is determinative in this application wherein the lens units are fairly close to the heat sink surfaces within the elongated housing  12 . 
     Many variables affect the selection of material for the lens and the production of the lens. These factors include (a) the purity of the material, which must have the clarity of pure water (“water clear”); (b) the density of the material vs. the computer model of it; (c) the dimensions and tolerances of the lens; (d) the response of the material to temperature changes and nearby heat sources; (e) the method of manufacture; and (g) the produceability of details of the lens surface in a cost effective die and process. An additional consideration is the material selected for the over lens components ( 24 ,  28  in  FIG. 1 ) which is also polycarbonate. Important factors in the selection of the material for the over lens  24 ,  28  are light transmission ability, refractive index n, and the distance between the lens assembly  104  and the over lens  24  or  28 . 
     The lens assembly  100 , or, simply, lens  100 , is shown in cross section in  FIG. 4A  as aligned along its centerline or optical axis  102 . The lens  100 , when implemented as a molded or cast solid body unit, is bounded by several surfaces, all concentric about or centered on the optical axis  102 . Further, as shown in the figure, the lens  100  is oriented to the right, defined as the forward direction  104  of the emission of light from the lens  100 . When an active light emitting device is located at a focal point  106  of the lens  100 , the emitted light is reflected and refracted in the lens to direct it in the forward direction  104  and disperse the light uniformly within a cone-shaped beam along the optical axis  102 . The cone-shaped beam is said to have a beam width defined by the beam angle β. In the preferred embodiment, the beam angle β is approximately 40°. Although such lenses are frequently known as “collimating lenses,” this term is only accurate if the light rays forming the beam emerge from the lens substantially in parallel. In the lens  100 , the light rays emerge from the lens  100  in angles relative to the optical axis varying from zero to approximately 20°+/−5°. This angle is often called the “half angle” of the beam, denoted herein by the Greek letter α. The beam angle denoted by β is thus equivalent to two times the half angle α. The beam emitted from the lens  100  will be further described with  FIG. 4C . 
     Continuing with  FIG. 4A , the optical properties of the lens  100  are determined by five kinds of surfaces, all of which are located at the physical boundaries of the lens  100 . The first surface to be described is an aspherical reflecting surface  108  having a focal point  106  on the optical axis  102 . The aspherical reflecting surface  108  reflects light rays emitted from a light emitting source located approximately at the focal point  106  in the forward direction and comprises substantially all of the outer boundary of the lens  100 . The reflecting surface  108 , having a curved profile defined by an aspherical polynomial, provides total internal reflection of light rays emitted from the light emitting source located at or near the focal point  106  that exceed a so-called “critical angle” to be defined herein below. The polynomial may generally be of the form of a parabola or other generalized polynomial and may readily be defined by persons skilled in the art using optical design software available for the purpose. For example, in the illustrated embodiment, the curve of the aspherical reflecting surface  108  is of the general form
 
 y=a+b   1   x+b   2   x   2   +b   3   x   3 .
 
As will be understood by persons skilled in the art, the coefficients of the independent variable x in the above equation may be chosen based on the particular surface profile desired.
 
     A second boundary of the lens  100  may be defined by a spherical refracting surface  110  disposed in the path of light rays emitted from the source, centered on and normal to the optical axis and positioned there along so that the light rays emerging from the lens  100  within a predetermined angle—the aforementioned half angle α—with respect to the optical axis  102 . The spherical refracting surface  110  is concave in the forward direction. The radius of the surface  110  in the illustrative embodiment is 17.0 mm relative to a point forward of the surface  110  along the optical axis  102  and its outer perimeter intersects the outer perimeter of the aspherical reflecting surface  108  at a radius of 9.36 mm from the optical axis in the illustrated embodiment. The outer perimeter of the surface  110  is defined at a distance of 11.65 mm forward of the plane normal to the optical axis at the rear-most boundary edge  114  of the lens  100 . The spherical refracting surface  110  may further include a plurality of N concentric, ring-like annular surfaces  120 , each annular surface having a cross section that is convex in the forward direction and disposed substantially at uniform radial intervals between the optical axis and the intersection with the aspherical reflecting surface. The purpose of the N concentric annular rings  120  is to provide correction for corona that appears just outside the principle beam pattern illustrated in  FIG. 3 . This “Gaussian” correction minimizes the corona and improves the uniformity of the distribution of light within the composite beam cross section provided by the PLD  10 . The number and dimensions of the annular rings  120  are determined empirically for a given application. The cross section of each of the annular rings  120  may be substantially hemispherical. In the illustrated embodiment, centered along the optical axis and within the smallest diameter annular ring, a fragment of a hemispherical surface  122  may be provided to adjust the beam pattern falling on a distant object. At least N=3 annular surfaces have been found to be a suitable number, with N=7 to be preferable, as shown in  FIG. 3 , for the target distances of three to four meters. 
     A third boundary of the lens  100  may be defined by a hollow cylindrical surface  112  having a longitudinal axis coincident with the optical axis  102 , disposed within the aspherical reflecting surface  108 , and extending in the forward direction  102  from a plane normal to and intersecting the optical axis  102  approximately at the rear-most boundary edge  114  of the lens  100 . The cylindrical surface  112  also defines a hollow interior space  130  that extends to a distance  116  of approximately 5.15 mm from the plane normal to the rear-most boundary edge  114 . As will be described herein below, the boundary edge  114  serves as a seat against which a light emitting assembly makes contact with the lens  100 . Further, the distance  116  is defined by the circumferential point around the radius of the cylindrical surface  112  that also lies on the surface of a reference cone having the same diameter at that point as the cylindrical surface  112  and an apex at the focal point  106 . It is along this circumferential point that an aspherical refracting surface  118  (to be described) intersects the cylindrical surface  112 . This distance of this circumferential line of intersection (between the cylindrical  112  and aspherical refracting  118  surfaces) from the normal plane  114  is determined by a “critical angle” (shown in  FIG. 4C ) defined as one-half of the included angle (i.e., the beam width angle β) of the reference cone. 
     The critical angle α, in the context of the present discussion, refers to the included angle of light emission from a light source located at the focal point  106  within which the emitted light would not be reflected by the aspherical reflecting surface  108 . The critical angle α is equivalent to the half angle of the beam of light that emerges from the lens  100 , and corresponds to an optimum beam cross section that, when merged with identical beams from a specified number of like light emitting sources arranged in a closely-spaced array, provides the brightest, most uniformly illuminated pattern of projected light. The critical angle α for producing a high-brightness, uniform projected beam is an empirically determined function of the number of light emitters and the characteristics of the lens elements used for the emitters. Generally, high brightness is achieved with multiple light emitting devices arranged to project overlapping individual beams of light on the target surface. The critical angle α can be thought of as an angle of disposition that defines the beam cross sections of the individual lenses for the light emitting devices, and may be different for each lens when the number of light emitting devices used in a particular array is different. The number of light emitting devices used in a particular array depends on various factors such as product packaging, available power, heat dissipation, the target distance, manufacturing costs, etc. 
     A fourth boundary of the lens  100  may be defined by an aspherical refracting surface  118  disposed in the path of light rays emitted from the source and centered on and normal to the optical axis. Further, the surface  118  is positioned along the optical axis  102  so that light rays emerging from the light source located at the focal point  106  and within the critical angle α with respect to the optical axis  102  are properly directed by the spherical refracting surface  110  to emerge from the lens  100  within the required half angle to produce the desired beam width angle β. In the illustrated embodiment the aspherical refracting surface  118  is a parabola concave in the forward direction and its outer perimeter intersects the outer perimeter of the cylindrical surface  112  at a boundary equidistant from the optical axis and at an appropriate linear distance along the optical axis  102  that is defined by the critical angle α. 
     It should be appreciated that the combination of the four kinds of concentric surfaces  108 ,  110 ,  112 , and  118  described herein above—all surfaces of revolution about the optical axis  102  form and define the outer surface, i.e., the physical boundaries, of the lens  100 . It will also be apparent that the four lens surfaces are maintained in a fixed relationship with each other in all copies of the lens  100  because of the solid body construction of the lens  100 . This construction provides ruggedness, repeatability, and is amenable to the use of simple manufacture and assembly processes as will be appreciated by persons skilled in the art. Other features of the lens  100  include a circumferential ridge  124  surrounding the perimeter  128  of the lens  100 . The ridge  124  includes a forward face  126  for use as a mounting surface. The mounting of the lens  100  will be further described with  FIG. 8B . The hollow space  130  within the cylindrical surface  112  provides space for certain structural elements of the light emitting device to be described herein below. 
     The fifth kind of surface at the boundaries of the lens  100  is the compound surface profile resulting from the combination of the spherical refracting surface  110  and the series of annular rings  120  as shown in  FIGS. 4A and 4B . 
     Referring to  FIG. 4B , there is illustrated an enlarged cross section of a portion of  FIG. 4A  to show details thereof. A portion of the spherical refracting surface  110  is shown, having superimposed thereon the partially hemispherical cross section of three adjacent annular ring surfaces  120 . The illustration in  FIG. 4B  clearly shows the radial separation between adjacent annular ring surfaces  120 . In the illustrated embodiment, the spherical refracting surface  110  has a radius of 17.0 mm relative to a point along the optical axis  102  forward of the lens  100 . Each annular ring  120 , spaced at 1.338 mm intervals, has a cross section radius of 1.60 mm. The flat portion of the spherical refracting surface  110  between each annular ring  120  is approximately 0.25 mm. 
     Referring to  FIG. 4C , there is illustrated a cross section profile of the solid body lens  100  of  FIG. 4A  in combination with a light emitting device assembly  139  (which may also be called LED assembly  139  or LED unit  139 ). The light emitting device assembly  139  includes the light emitting device  140 , the base  142 , the hemispherical shell  144 , and the substrate  146  as will be described. The combination of the solid body lens  100  and the LED assembly  139  will be called the lens/LED assembly  155  herein below. In the description which follows, a plurality of the lens/LED assemblies  155  will appear in some figures being described, but not separately identified in the figures with the reference number  155  to avoid confusion with the structures being described and their relationship with each other. Structures shown in  FIG. 4C  having the same reference numbers used in  FIGS. 4A and 4B  are identical.  FIG. 4C  thus includes a light emitting device  140  (shown in phantom) mounted on a base  142 . The light emitting device  140  is enclosed within a transparent hemispherical shell  144  mounted on the base  142  such that the center of the hemispherical shell is coincident with the emitting point of the light emitting device  140 . The base  142  is in turn mounted on a substrate  146 . The base  142  and the hemispherical shell  144  are typically integral parts of the semiconductor package containing the light emitting device  140  (in this case a light emitting diode). The substrate  146  may be a printed circuit board. In the illustrative embodiment the substrate  146  is a laminated structure of a printed circuit and an aluminum base layer that acts as a heat sink. One suitable LED assembly  139  is a Luxeon® type LXHL-PW01 white, Lambertian emitter available from the Lumileds Lighting, Inc., San Jose, Calif., USA. This emitter is also available as an assembly (including the emitter, base, substrate, and hemispherical shell) as a Luxeon® type LXHL-MW1D “Star Base” with the white, Lambertian emitter. The “Star Base” configuration corresponds to the LED assembly  139  described herein. In alternative embodiments, the LED  140  in the LED assembly  139  may be an incandescent light emitting bulb, a gas discharge light emitting unit, an arc discharge light emitting unit, a halogen light emitting bulb, a fluorescent light emitting unit, an organic light emitting unit or a light emitting unit that emits light through any physical mechanism when initiated or driven by an electrical power source. 
     The light emitting device assembly  139  or LED unit  139  is typically available as a preassembled LED unit  139  from the manufacturer, assembled at the factory in planar arrays on a single printed circuit substrate for shipment to the customer. The customer need only separate or ‘break off’ a small section of the planar array, for example, a strip of four LED units  139 , for assembly into products that employ an LED unit  139 . In other applications, individual LED units  139  may be separated for installation in a product. An example of the latter is the illustrated embodiment (See, for example,  FIG. 8D  infra) wherein each LED unit  139  in an array of a plurality of LED units  139  is installed in a recessed area having a different angular orientation than the other LED units  139  in the array. 
     Returning to the description of the lens/LED assembly  155  of  FIG. 4C , when assembled together with the lens  100 , the transparent hemispherical shell  144  fits within the inside diameter of the cylindrical surface  112 . The base  142  of the light emitting device  140  is placed against the rear-most edge  114  of the lens  100 . This places the light emitting device (LED)  140  approximately at the focal point  106  of the aspherical reflecting surface  108 , in the correct position for light emitted from the LED  140  to be formed by the lens  100  into the beam of light having the characteristics previously described. It will be appreciated that the transparent hemispherical shell  144 , since its center is coincident with the point of emission of the light from the LED  140 , passes the emitted light substantially without reflection or refraction into the space  130  bounded by the cylindrical surface  112  and the aspherical refracting surface  118 . Light emitted within the critical angle α passes through the aspherical refracting surface  118 . Light emitted outside the critical angle α passes through the cylindrical surface  112  or is reflected toward the aspherical refracting surface  118 . The critical angle is shown in  FIG. 4C  as the angle α between the optical axis  102  and the dashed lines  148  and  150 . In the preferred embodiment, the critical angle α, which is equivalent to the half angle of the beam width, is 20°+/−5°, and the beam width β is equal to twice the critical angle α or 40°+/−10°. Light passing through the cylindrical surface  112  will thus be reflected by the aspherical reflecting surface  108  before being refracted by the spherical refracting surface  110  as it exits the lens  100 . The dashed boundary lines  152  and  154  define the nominal boundary of the beam of light emitted by the lens  100 . The boundary lines  152  and  154  of the light beam are parallel to the lines  148  and  150  illustrating the critical angle α. 
     To summarize several of the features of the optical system of the illustrative embodiment of the present invention, a unitary lens and light emitting device combination (lens/LED assembly  155 ) is provided that produces a highly uniform beam of light, corrected for distortions and gaps in illumination, throughout a full beam width angle β in the range of 40°+/−10°. This lens/LED combination or light source unit is illustrated herein to demonstrate its use in arrays of such light source units to provide optimum flood illumination from a portable, hand held task lamp product. The unitary lens may be formed as a solid body plastic lens which incorporates all of the necessary optical surfaces in a single piece unit, including the pattern-correcting spherical refracting surface, concave in the forward direction of illumination, that smooths out intensity variations in the overall illumination pattern. The light source unit provided by this lens/LED combination may be used singly or arranged in many different arrays formed of a plurality of such light source units for use in a wide variety of applications. 
     Referring to  FIG. 5 , there is illustrated a block diagram of an electrical circuit  160  for use in the embodiment of  FIG. 1  for powering and controlling the light outputs thereof. The purpose of the circuit is to drive two different arrays of LEDs, the first array and the second array, each at a constant brightness, from a single drive circuit. Driving each of the arrays at a constant brightness from the single drive circuit requires providing a constant current to the respective arrays, which may require different current levels to provide the specified brightness for the particular illumination pattern. The current levels are independently regulated for each array of LEDs by the electrical circuit. Further, the array of LEDs to be utilized is selected by operation of switches in the circuit by the user. The first array in the illustrated embodiment includes a plurality of LEDs and provides a flood light illumination. The second array in the embodiment example includes at least one LED and provides a spotlight illumination. The basic circuit includes a DC supply voltage  162 , a current selector circuit  172 , a switching regulator circuit  182 , and first  192  and second  202  arrays of light emitting devices (LEDs). Optional circuits, which will be described separately, include a strobe circuit  240 , a dimming circuit  260 , and a low battery indicator  270 . 
     The DC power supply  162  includes a positive terminal  164  and a negative terminal  166 . The positive terminal  164  is connected to a positive supply voltage bus  168 , which may also be called a supply bus  168  herein. The negative terminal  166  is connected to a negative supply voltage bus  170 , which may also be called a common bus  170  herein. In the illustrative embodiment, three rechargeable, 1.2 Volt, “D” cell, nickel-metal-hydride (NiMH) cells are utilized to provide the DC power supply for the PLD  10 . The current selector circuit  172  includes an input terminal  174 , a common terminal  176 , and an output terminal  178 . The input terminal  174  is connected to the supply bus  168  and the common terminal  176  is connected to the common bus  170 . The switching regulator circuit  182  includes an input terminal  184 , a common terminal  186 , and an output terminal  188 . The input terminal  182  is connected to the output terminal  178  of the current selector circuit  172  through a node  180 . The common terminal  186  of the switching regulator circuit  182  is connected to the common bus  170 . 
     Continuing with  FIG. 5 , the first array of LEDs  192  includes a positive terminal  194  and a negative terminal  196 . The positive terminal  194  is connected to the output terminal  188  of the switching regulator  182  through a node  190 . The negative terminal  196  of the first array of LEDs  192  is connected though a node  198  and a series current sense resistor  200  to the common bus  170 . The second array of LEDs  202  includes a positive terminal  204  and a negative terminal  206 . The positive terminal  204  is connected to the output terminal  188  of the switching regulator  182  through the node  190 . The negative terminal  206  of the second array of LEDs  202  is connected though the node  198  and the series current sense resistor  200  to the common bus  170 . The current sense resistor  200  may also be called a common current sense resistor  200 . The sense resistor  200  may also be called a common current sense device  200  herein because, in some embodiments, the resistor may be replaced by other elements such as an active circuit. 
     Working backwards through the basic circuit just assembled, a few other details will be described. The second array of LEDs  202  includes an input terminal  208 , which is connected through a series resistor  216  to a drive output  218  of the current selector circuit  172 . The signal coupled from the drive output  218  is a control signal to be described infra. The first array of LEDs  192  also includes an output terminal  210 , which is connected through a node  212  to a sense input  214  of the switching regulator circuit  182 . The current selector circuit  172  includes a first control terminal  220  and a second control terminal  230 . Connected between the first control terminal  220  and the common bus  170  is a first SPST switch  222 . Connected between the second control terminal  230  and the common bus  170  is a second SPST switch  232 . 
     The first  222  and second  232  switches respectively provide ON/OFF control of the first  192  and second  202  arrays of LEDs. Both switches  222  and  232  may preferably be single pole, single throw (SPST), normally open (N.O.) switches. In  FIG. 5  (and also in  FIG. 6A ), the symbols for the first  222  (SW 1 ) and second  232  (SW 2 ) are N.O. switches shown with their contacts in the closed position. This is correct as will become apparent in the description to follow. In the preferred embodiment, the first and second switches  222  and  232  are actuated with a push ON, push OFF switching action. The actuator is preferably operated by a push button. However, in other embodiments a lever, rocking button, rotating collar, or any type of actuator having a back-and-forth travel or a repeating rotational travel may be employed. Still other embodiments may employ touch-sensitive or proximity sensitive switch mechanisms requiring no moving parts. Switches having no moving parts or latching mechanisms may require a programming feature to provide the required action described herein as will be apparent to persons skilled in the art. As will become apparent in the description for  FIG. 6A  to follow, the first  222  and second  232  switches are operated in a non-obvious manner that provides three operating states for each SPST, N.O. switch: OFF, momentary ON, and ON. 
     Continuing with  FIG. 5 , a strobe circuit  240 , which may be provided as an optional circuit to operate the first and second LED arrays of the PLD  10  in a continuous or strobed (flashing) mode, includes a positive terminal  242  connected to the supply bus  168 , and a negative terminal  244  connected to the common bus  170 . A switch terminal  246  on the strobe circuit  240  is coupled to the common bus  170  through a strobe switch  248  (also called SW 3 ). The strobe switch  248  is preferably a SPST switch having normally closed (N.C.) contacts, and provides ON/OFF control to the strobe circuit  240 . An output terminal  250  of the strobe circuit  240  is connected via a line  252  to an input terminal  254  of the current selector circuit  172 . The strobe circuit  240  includes an oscillator which supplies a gating signal via the line  252  to control the current selector circuit  172  when activated by the strobe switch  248 . 
     A dimming circuit  260  may be provided as an option to control the brightness of the first  192  or second  202  array of LEDs. It is available primarily as a power saving feature but may also be useful when the high brightness available from either of the LED arrays  192 ,  202  is not needed. An example would be when the target area to be illuminated by the PLD  10  is closer than three to four meters. The dimming circuit  260  includes a first terminal  262  and a second terminal  264 . The first terminal  262  is connected to the node  212 . As will be described herein below, node  212  is a connection point to the current sense circuit for the first  192  and second  202  arrays of LEDs. The second terminal  264  of the dimming circuit  260  is connected through a SPST switch  266  having N.O. contacts to the node  180 . The switch  266  (also called (SW 4 ) may be a push ON, push OFF switch for activating or deactivating the dimming circuit. 
     A low battery indicator circuit  270  having a positive terminal  272  and a negative terminal  274 , respectively connected to the supply bus at node  180  and to the common bus  170 , may be included in the illustrated embodiment of the PLD  10 . The DC supply voltage  162  in the illustrated embodiment of the PLD  10  is provided by a battery pack. As will be described, the low battery indicator circuit  270  senses the voltage available at the node  180  and provides a visual indicator when the terminal voltage of the battery pack drops to a predetermined threshold. 
     Referring to  FIG. 6A , there is illustrated a first portion of a schematic diagram of the electrical circuit of  FIG. 5 . Some of the structural features of  FIG. 6A , previously described in  FIG. 5  and identical therewith, bear the same reference numbers. Other structures in  FIG. 6A  having a counterpart in  FIG. 5  will be so identified. For example, the positive supply bus  300  in  FIG. 6A  is the counterpart of supply bus  168  in  FIG. 5 , and the common bus  302  is the counterpart of the common bus  170  in  FIG. 5 . Several key structures of  FIG. 6A  having counterparts in  FIG. 5  will include the counterpart reference number in parentheses, as  300  ( 168 ),  302  ( 170 ), and so on. 
     Continuing with  FIG. 6A , a battery  310  ( 162 ) is connected to the circuit  160 , its positive terminal connected through a resettable fuse  308  to the node  300  ( 168 ) and its negative terminal connected to the node  302  ( 170 ). The node  300 ( 168 ) provides the connection to the positive supply voltage bus  300 ( 168 ), also known as the supply bus  300 ( 168 ). The node  302 ( 170 ) provides the connection to the negative supply voltage bus  302 ( 170 ), also known as the common bus  302 ( 170 ). A capacitor  312  connected between the nodes  300  and  302  absorbs transients and noise from the supply  300  ( 168 ) and common  302  ( 170 ) buses. A quad NAND gate  314  (also called U 1 ), which may be a type 74AC00SC integrated circuit, is coupled with a P-channel FET transistor  316  (also called Q 1 ), which together function as the current selector  172  of  FIG. 5 . The P-channel FET  316  may be rated at 4.5 Amperes, 20 volts in the illustrated embodiment. 
     The quad NAND gate  314  is connected in the electrical circuit  160  as follows. As a preliminary condition, the FET  316  is connected in the supply bus  300 ( 168 ) between the nodes  300  ( 168 ) and  304  ( 180 ) as follows. The drain terminal of the FET  316  is connected to the positive terminal of the battery  310  ( 162 ) via the node  300  ( 168 ). The source terminal of the FET is connected to the load side of the FET  316  at a node  304  ( 180 ). The gate terminal of FET  316  is connected to the respective anodes of first  318  and second  320  steering diodes. The cathodes of the first  318  and second  320  steering diodes are connected to output pins  3  and  11  of the first  314 A and second  314 B NAND gates in the quad NAND gate  314  (U 1 ). The positive supply or Vcc terminal  14  of the quad NAND gate  314  is connected to the supply bus at node  300 ( 168 ). The negative supply or Vss terminal of the quad NAND gate  314  (U 1 ) is connected to the common bus at node  302 ( 170 ). 
     Pins  2  (of the first NAND gate  314 A (U 1 A)) and  13  (of the second NAND gate  314 B (U 1 B)) are connected together at a node  254 . Node  254  is connected to a node  250 . Node  250  is connected to the supply bus  300  ( 168 ) through a pull up resistor  374 , and also to the output pin  3  of a gated oscillator  364  (integrated circuit U 4 ). The gated oscillator  364  is part of an optional strobe circuit to be described. Without the strobe circuit in place, the node  250  is tied to the positive supply voltage at node  300  ( 168 ) through the pull up resistor  374 . The pull up resistor is provided to maintain pins  2  and  13  of the first  314 A and second  314 B NAND gates at a logic HIGH, unless the pins  2  and  13  are required to be driven LOW by the action of a signal applied to the node  254  to provide an auxiliary control function. Such an auxiliary control function may include a strobe function or any other function that requires interruption of current to the illumination drive circuitry that may be included in a particular embodiment. The interruption to the drive circuitry may be timed, as for providing a strobe function, or untimed, to provide a temporary OFF condition under manual control, for example. The operation of a strobe circuit, identified by reference number  240  in  FIG. 5 , will be described later to illustrate the control effect of signals present at node  254 . 
     Continuing with  FIG. 6A , the inputs  9  and  10  (tied together) of the third NAND gate  314 C (U 1 C), shown configured to operate as an inverter, are coupled to the output pin  11  of the second NAND gate  314 B (U 1 B). This arrangement provides a separate, second drive signal to control the operation of the second array  202  of LEDs. The second array  202  of LEDs is enabled to operate when selected by pressing the second ON/OFF switch  232 , causing the output of the second NAND gate to go LOW and the output pin  8  of the third NAND gate  314 C (U 1 C) to go HIGH. A HIGH output from the third NAND gate  314 C (U 1 C) will cause a second N-channel FET  360  (Q 3 ) to conduct, thereby causing the second array  202  of LEDs to illuminate, as will be described. As this occurs, and as will be described, the first array  192  of LEDs will not be activated even though it has been enabled by pressing the first switch  222 . 
     The operation of the current selector  172  in  FIG. 6A  proceeds as follows. The first NAND gate  314 A (U 1 A) and the second NAND gate  314 B (U 1 B), are respectively operated by the first  222  and second  232  ON/OFF switches (SW 1  and SW 2 ) to gate ON or OFF the FET  316  that is coupled in series with the positive DC supply voltage on the supply bus  300 ( 168 ). The outputs of the first  314 A and second  314 B NAND gates are connected via the respective steering diodes  318  and  320  to the gate of the FET  316 . If the output of either the first  314 A or second  314 B NAND gate is a logic LOW, the FET  316  is enabled to conduct current, thus supplying operating current to the switching regulator circuit  182 . As an initial condition, the input pin  2  of NAND gate  314 A and pin  13  of NAND gate  314 B, which are tied together at node  254 , are held HIGH by the action of resistor  374  and the respective inputs, pins  1  and  12  of the NAND gates  314 A and  314 B are held LOW by the action of the first  222  and second  232  ON/OFF switches. (An exception to this condition, to be described infra, occurs when a strobe circuit  240  is included in the circuit and has been activated.) From this initial condition, the output pin  3  of the first NAND gate  314 A switches LOW when the first ON/OFF switch  222  is pressed, opening its contacts and causing a HIGH signal at input pin  1  of U 1 A by the action of resistor  322 . Similarly, the output pin  11  of the second NAND gate  314 B switches LOW when the second ON/OFF switch  232  is pressed, opening its contacts and causing a HIGH signal at input pin  12  of U 1 B by the action of resistor  324 . In this way, operating current for either of the first  192  or second  202  LED arrays is supplied to the switching regulator  182  by causing the FET  316  to conduct. 
     The foregoing operation of the first  222  and second  232  ON/OFF switches demonstrates the unusual use of the SPST, N.O., push-ON, push-OFF switches having first and second contacts to provide three operating states. The usual application of this type of switch is a first state in which the contacts are disengaged, thus disconnecting the circuit path in which the switch is used, and a second state in which the contacts are engaged, thus connecting the circuit path in which the switch is used. However, in the present invention, each of these SPST switches is sequentially operable in the first, second, and third states corresponding respectively to latched engagement of the contacts of the switch, momentary disengagement of the contacts of the switch, and latched disengagement of the first and second contacts of the switch. In this sequence, the first state (contacts engaged) operates to place the electric circuit in an OFF condition, the second state (contacts disengaged but not latched) provides activation of the electric circuit in a momentary ON condition, and the third state (contacts disengaged and latched) provides activation of the electric circuit in a latched ON condition. The first state corresponds to non-operation of the switch. Pressing the push button of the switch with less pressure than necessary to cause it to latch moves the contacts from a closed (engaged) condition to a momentarily open (disengaged) condition, which is the second state. Pressing the push button of the switch with sufficient pressure to cause it to latch moves the contacts from a closed (engaged) condition past a detent in the switch mechanism to a latched open (disengaged) condition, which is the third state. As noted previously, when the contacts are disengaged, the current selector circuit is turned ON to supply current to the first or second array of LEDs depending upon which of the two ON/OFF switches was pressed. Conversely, when the contacts are engaged, the FET  316  is turned OFF, inhibiting the current supply to the first or second array of LEDs. 
     Before describing the operation of the switching regulator circuit  182 , some characteristics of the first  192  and second  202  LED arrays need to be described. In the illustrated embodiment, semiconductor light emitting diodes are selected for the light emitting devices of the PLD  10 . For the first array  192 , four each white, 1 watt, Lambertian emitter, Luxeon® type LXHL-PW01 (or type LXHL-MW1D “StarBase” as described herein above), available from Lumileds Lighting, Inc., San Jose, Calif. is suitable. Typical values for the forward current and voltage in the 1 watt device are 0.35 Amperes and 3.42 Volts respectively, corresponding to a typical light output of 25 lumens (25 lm). For the second array  202 , one each white, 3 watt, Lambertian emitter, a Luxeon® III type LXHL-PW09 (or type LXHL-LW3C “Star Base”), also available from Lumileds Lighting is suitable. Typical values for the forward current and voltage in the 3 watt device are 1.0 Amperes and 3.70 Volts respectively, corresponding to a typical light output of 80 Lumens (80 lm). Thus, the operating current for the first array  192  is approximately 0.35 Amperes and the forward voltage drop is approximately 4×3.42 Volts or 13.68 Volts, resulting in an approximate power utilization of the array of 4.8 watts. Similarly, he operating current for the second array is approximately 1.0 Amperes and the forward voltage drop is approximately 3.70 Volts, resulting in an approximate power utilization of 3.70 watts. 
     The foregoing figures for operating currents and power levels in the illustrated embodiment are typical values that conform approximately with the manufacturer&#39;s published specifications. In the illustrative embodiment, the second array may be operated at slightly higher current, for example, 1.10 to 1.40 Amperes, to obtain power utilization in the four to five watt range to provide greater light output for the spot light array. In one exemplary unit, the current for operating the first array  192  is approximately 0.36 Amperes as regulated by the current selector circuit  172  including the quad NAND gate  314 . Further, the current for operating the second  202  array is approximately 1.30 Amperes as regulated by the control circuit  330 . Keeping these current and voltage drop values in mind will inform the description of the switching regulator. Persons skilled in the art will readily understand that a wide variety of lens/LED combinations (of numbers of light emitting sources and arrays of light emitting sources) and operating power levels are possible using the principles described herein. An important feature of the switching regulator described herein is that it drives two disparate loads with constant currents from a single drive circuit. 
     The first array  192  of LEDs is enabled whenever current is supplied to the switching regulator  182 . This may occur upon the pressing of either the first  222  or the second  232  ON/OFF switch because either condition results in a LOW applied to the gate of the FET  316  in the current selector circuit  172 . In the illustrated embodiment, the first array  192  of LEDs has more LEDs in series across the output of the switching regulator than the second array  202  of LEDs. The electrical circuit  160  is arranged so that the first array  192  of LEDs will be activated by the output of the switching regulator circuit  182  unless the second array  202  of LEDs is activated. This result occurs because the voltage drop across the fewer devices in the second array  202  of LEDs is less than the voltage drop across the greater number of devices in the first array  192 . If the second array  202  is activated there will be insufficient voltage from the constant current switching regulator circuit  182  to activate the first array  192  of LEDs and the LEDs of the first array  192  will be in an OFF condition. To look at it another way, when the second array  202  of LEDs is activated, it shunts current away from the first array  192  of LEDs. The PLD  10  as described herein takes advantage of this configuration as follows. The circuit of the current selector  172  includes a third NAND gate  314 C (U 1 C) that responds to the operation of the second switch  232  by causing a LOW signal to be present at the output pin  11  of the second NAND gate  314 B (U 1 B). As a result, the output of the third NAND gate  314 C goes HIGH to enable the second array  202  of LEDs. 
     Referring to  FIG. 6B , there is illustrated a second portion of the schematic diagram of the electrical circuit  160  of  FIG. 5 .  FIG. 6B  includes the switching regulator circuit  182 , the first array  192  of LEDs and the second array  202  of LEDs. Some of the structural features of  FIG. 6B , previously described in  FIG. 5  and identical therewith, bear the same reference numbers. As with  FIG. 6A , several of the structures in  FIG. 6B  having a counterpart in  FIG. 5  will be so identified. The switching regulator circuit  182  of the illustrated embodiment is provided by a step-up flyback converter architecture that includes an integrated control circuit  330  (U 2 ) having a positive Vcc terminal pin  1  coupled to the supply bus at node  184  and a ground terminal pin  2  (node  182 ) connected to the common bus  302  ( 170 ). 
     An inductor  342 , 6.8 microHenry (uHy) in the illustrated embodiment, is connected in series between the node  184  and a node  336 . A 3 Ampere, 100 volt, fast switching diode  344 , is connected between the node  336  and a node  306 . The inductor  342  and the switching diode  344  are connected in series with the voltage supply bus  178  at the output of the current selector  172 . A 47 microFarad (uF), 25 volt filter capacitor  348  is connected between the node  306  ( 188 ) and the common bus at node  302  ( 170 ), effectively the output terminals of the switching regulator  182 . Capacitor  348  is used if it is desired to drive the first  192  or second  202  arrays of LEDs with a DC voltage. However, the circuit may be operated without the capacitor  348 . Without capacitor  348 , the switching regulator provides a pulsed drive to the arrays  192 ,  202  of LEDs. The duty cycle at maximum available voltage is approximately 50%; the duty cycle when operating at minimum voltage is approximately 90%, at the operating frequency of approximately 100 Khz. 
     Connected between the node  336  and the common bus node  302  ( 170 ) is a first switching transistor, N-channel FET  334  (Q 2 ), rated at 14 Amperes, 50 volts. The drain terminal of the FET  334  is connected to the node  336  and the source terminal of the FET  334  is connected to the common bus  302  ( 170 ) through a very small-valued (0.0075 Ohms in the present embodiment) series resistor  340 . The source terminal of the FET  334  is also connected to pin  4  (a current sense terminal) of the integrated control circuit  330 . The gate terminal of the FET is connected to pin  6  (the drive voltage output terminal) of the integrated control circuit  334 . Pin  5  (a voltage feedback terminal) of the integrated control circuit  334  will be described later. The integrated control circuit  334  may be, for example, a “regulated, voltage mode converter,” type ZXSC400 available from Zetex Inc., Hauppauge, N.Y. 11788. The ZXSC400 provides a programmable constant current output for driving an array of LEDs such as one or more light emitting diodes. In embodiments of the PLD  10  using other types of LEDs, the switching regulator circuit  182  may be changed to match or adapt to the particular characteristics of the LEDs. 
     The switching regulator  182  in the embodiment illustrated herein operates as follows. When power is first applied to the control circuit  330 , the drive signal at the output pin  6  appears at the gate of the first FET  334 , turning the FET  3340 N. Current ramps up through the inductor  342 , the FET  334 , and the series resistor  340 , charging the inductor  342  until the voltage across the resistor  340  reaches 30 millivolts (mV). At that point, the FET is biased OFF and the flyback action of the inductor  342  dumps the energy stored in its magnetic field as a current through the fast switching diode  344 , charging the filter capacitor  348  to the peak value of the voltage available at the node  306  ( 188 ). This voltage is available to drive the first  192  and second  202  arrays of LEDs according to whether the first  222  or the second  232  ON/OFF switch is activated. Meanwhile, the circuitry within the control circuit  330  and connected to the feedback pin  5  monitors the voltage present at pin  5 . Whenever the voltage at pin  5  exceeds 300 mV, the FET  334  will be gated OFF for approximately 2.0 microseconds (2.0 usec). After this time period expires, and the voltage at pin  5  falls below the 300 mV value, the FET  334  will be gated ON again. This sequence is repeated, which stabilizes the voltage at pin  5  of the control circuit  330  at the 300 mV level and the current delivered to the first  192  or second  202  array of LEDs is maintained at a constant level determined by the value of the inductor  342  and the resistor values selected for the current sensing network comprising the resistors  354  and  356 . 
     The first  192  and the second  202  arrays of LEDs, along with the current sensing network will now be described before completing the description of the operation of the switching regulator circuit  182  when performing its current regulating functions. The first array  192  of LEDs in the illustrative embodiment is a series circuit connected between a node  190  and the common bus at the node  302  ( 170 ). The series circuit includes a string  350  of four light emitting diodes of like characteristics connected to be forward biased between the node  190  and a node  352 . The anodes of the string  350  of the light emitting diodes are all oriented toward the node  190  and the cathodes are oriented toward the node  352 . A lead or terminal  194  connects the anode of the uppermost light emitting diode to the node  190 . A current sense resistor  354  is connected between the node  352  and through a terminal  196  to a node  198 . A common current sense resistor  356  is connected between the node  198  and the common bus at node  302 . A third sense resistor  358  is connected between the node  352  and the node  210  to the node  212 . The node  212  is connected to the feedback pin  5  of the control circuit  330  via the node  214 . 
     The feedback voltage at pin  5  is developed as follows. The resistor  356  is a common current sense resistor, developing a voltage drop proportional to the currents in both the first  192  and the second  202  arrays of LEDs. A second sense resistor  354 , in series with the first  192  array of LEDs and the common sense resistor  356 , provides a voltage at the node  352 , which is sensed at pin  5  through a resistor  358  and the nodes  210  and  212 . Pin  5  of the control circuit  330  is high impedance point in the circuit; thus, resistor  358  has little effect on the current sensing during normal operation. 
     The dimming circuit  260  may be provided as an option to control the brightness of the first  192  or second  202  array of LEDs for saving power or limiting brightness of output illumination of the PLD  10 . The dimming circuit  260  includes a first terminal  262  and a second terminal  264 . The first terminal  262  is connected to the node  212 . The second terminal  264  of the dimming circuit  260  is connected through a SPST switch  266  having N.O. contacts to the node  180 . The switch  266  (also called (SW 4 ) may be a push ON, push OFF switch for activating or deactivating the dimming circuit. In operation, under normal operating conditions without dimming the light output, the feedback voltage at pin  5  of the control circuit  330  is approximately 300 millivolts. Closing the contacts of the dimming switch  262  drives a current through the resistor  264 , thus increasing the voltage drop across the resistor  358 . this action increases the feedback voltage applied to pin  5  of the control circuit  330  sufficiently to reduce the current drive to the respective first  192  or second  202  LED array to cause the brightness level to decrease by approximately 50%. 
     The strobe circuit  240  of  FIG. 5 , shown in greater detail in  FIG. 6A , provides for operating the first  192  or second  202  arrays of LEDs in an alternating ON and OFF mode—i.e., flashing—at a fixed duty cycle and frequency. The timing provided is approximately 0.25 seconds ON and 1.0 second OFF. The heart of the strobe circuit  240  is a 555 timer circuit  364  operated as a gated oscillator. The timer circuit  364  is an 8-pin integrated circuit that includes a Vcc terminal  242  (pin  8 , which is tied to pin  4 ) connected to the supply bus  300  ( 168 ) and a Vss terminal  244  (pin  1 ) connected to the common bus  302  ( 170 ). Pin  2  is connected through resistor  368  and resistor  374  to the supply bus  300  ( 168 ). The junction of the resistors  368  and  374  is a node  250  that is connected to pin  3  of the timing circuit  364 . Pin  6  of the timing circuit  364  is connected to a node  246 . Node  246  is connected through a resistor  366  to the cathode of a signal diode  376 . The anode of the diode  376  is connected to the node  250 . Node  246  is further connected to the common bus  302  ( 170 ) via a SPST, normally closed (N.C.) switch  248  (also called SW 3  in  FIG. 6A ). Pin  5  of the timing circuit  364  is connected to the common bus  302  ( 170 ) via a capacitor  372  acting as a noise filter. As previously described, the node  250  is connected to the node  254 , which is the signal input for controlling the current selector  172  in either a continuous or strobe mode. 
     The strobe circuit  240  operates as follows. When the strobe switch  248  (SW 3 ), having N.C. contacts is in a released state, i.e., not pressed or activated, its contacts are closed and the output pin  3  of the timer circuit  364  is held HIGH by the action of the pull up resistor  374  at the node  250 . This signal is applied to pins  2  and  13  of the NAND gate  314 , providing the initial or quiescent condition for responding to the activation of the first  222  and second  232  ON/OFF switches during operation of the PLD  10 . When the strobe switch  248  (SW 3 ), having N.C. contacts is pressed or activated, its contacts are open, the voltage across the capacitor  370  rises until it exceeds a threshold value, and the output pin  3  of the timer circuit  364  is caused to switch to a logic LOW, removing the drive to the FET  316 . At that instant, the capacitor  370  begins to discharge toward zero. When the voltage across the capacitor  370  reaches the threshold voltage at pin  2  of the timer circuit  364 , the output at pin  3  of the timer circuit  364  switches back to a HIGH, causing the FET  316  to turn ON. The cycle repeats as long as the strobe switch  248  is activated. It is preferably a push ON, push OFF, latching type of switch that remains activated until it is pressed a second time after turning ON the strobe function. The timing of the cycle is set by the RC time constants of the capacitor  370  and the resistors  366  and  368 . As mentioned herein above, the current selector circuit  172  is held OFF for approximately 1.0 second and ON for approximately 0.25 second when the strobe circuit is activated. This timing sequence can of course be revised by changing component values to satisfy particular preferences. 
     Returning to  FIG. 6A , the circuit for the low battery indicator  270  of  FIG. 5  will now be described. The low battery indicator  270  includes a positive terminal  272  and a negative terminal  274 , respectively connected to the supply bus at node  304  in  FIG. 6B  ( 180  in  FIG. 5 ) and to the common bus  302  ( 170 ). The DC supply voltage  162  in the illustrated embodiment of the PLD  10  is provided by a battery  310  ( 162 ). In the illustrative embodiment, three rechargeable, 1.2 Volt, “D” cell, nickel-metal-hydride (NiMH) cells are utilized to provide the DC power supply for the PLD  10 . The circuit for the low battery indicator  270  senses the voltage available at the node  180  and provides a visual indicator when the terminal voltage of the battery pack  310  ( 162 ) drops to a predetermined threshold. The predetermined threshold is set to approximately 3.1 Volts, corresponding to a useful output for about one hour. 
     Continuing with  FIG. 6A , the node  272  represents the positive supply voltage connected to the output of the current selector circuit  172 . The node  272  is also the monitored point in the circuit  160  for tracking the available battery voltage. The node  274  represents the negative supply terminal connected to the common bus  302  ( 170 ). The indicator circuit utilizes an op amp  380  (also called U 3 ) connected as a comparator. Pin  7  of the op amp is connected to the node  272  and pin  4  is connected to the node  274 . The positive input pin  3  is connected to a node  382  and the negative input pin  2  is connected to a node  388 . The output pin  6  is connected to node  382  through a resistor  398  to provide some positive feedback to ensure a rapid transition when the op amp comparator switches. Pin  6  is also connected to the node  388  through a capacitor  400  to roll off the gain at higher frequencies so that the comparator is less sensitive to noise. Output pin  6  is further connected to the node  272  through a light emitting diode  402  in series with a resistor  404 . The positive input pin  3  tracks the DC voltage present at node  382 , the center of the voltage divider formed by resistors  392  and  394  connected between the nodes  272  and  274 . A capacitor  396  is connected from node  382  to node  274  to stabilize the DC voltage at node  382 . Also connected between the nodes  272  and  274  is a series circuit formed by a resistor  386  and a zener diode  390 . The junction of the resistor  386  and the zener diode  390  is node  388 , which applies the zener reference voltage of 2.50 volts to the negative input pin  2  of the op amp  380 . Thus, whenever the voltage at the node  382  drops below the reference voltage present at the node  388 , the output of the op amp switches from HIGH to LOW, causing sufficient current to flow in the light emitting diode  402 , indicating the low battery voltage condition. 
     To summarize several of the features of the electrical circuit of the illustrative embodiment of the present invention, a single drive circuit is configured to drive disparate current loads of first and second lighting arrays—combinations of compact light emitting devices—with the respective regulated constant currents. Further, a configuration of first and second standard push ON, push OFF, latching switches provides independent control of the two lighting loads wherein each switch operates in three states including momentary ON, continuous ON, and OFF. The circuit is readily adapted to providing continuous or pulsed drive to the lighting arrays. Also described are optional circuit features that provide a dimming control, a strobe control, and a low battery indicator. 
     Referring to  FIG. 7 , there is illustrated an exploded view  420  of major parts and assemblies of the embodiment of  FIG. 1 . The first  422  and second  424  elongated shells, when assembled together around the contents of the PLD  10  (See  FIG. 1 ) form an elongated tubular housing  12  (See  FIG. 1 ) having a longitudinal axis  14  (See  FIG. 1 ) approximately coincident with the centerline  406  of the battery pack  432 . A combination of a plurality of alignment tabs  408  distributed along each side of the second elongated shell  424  are placed to fit within complementary receptacles, such as that identified by reference number  410 , disposed in a plurality of corresponding locations along each side of the first elongated shell  422 , thus ensuring that the first  422  and second  424  shells are securely and correctly aligned upon assembly. The first  422  and second  424  shells are typically secured together using machine screws inserted in the locations  414  and elsewhere through surfaces not visible in  FIG. 7 . Further, resilient prongs  412  molded near the inside edges of the second elongated shell  424  near the first section  16  (See  FIG. 1 ) may be configured to spring into a locking relationship with corresponding ridges molded into the first elongated shell  422 , to further secure the first  422  and second  424  shells together prior to inserting the machine screws at the locations  414 . The alignment tabs and resilient prongs, in combination with the use of overmold gaskets applied during the manufacturing process (described two paragraphs infra), contribute to the overall strength and rigidity of the elongated housing structure. Such ruggedness is expected in a lighting product intended for the specific industrial markets listed below in the next paragraph. 
     The first  422  and second  424  elongated shells shown in  FIG. 7  may be preferably molded or cast from thermoplastic or metallic materials. In the illustrative embodiment, a general purpose, unreinforced polyetherimide resin (PEI) sold by G. E. Plastics under the brand name ULTEM®, 1000 series, may be used because of its heat resistance, dimensional stability, durability, very high strength and resistance to chemicals. It is much lighter than aluminum or steel, and does not make metallic sounds or produce sparks when contacting other objects. These are important characteristics in a product intended for use in all kinds of weather and environmental conditions by security personnel, service truck persons, military, police, fire, EMS, and CSI units, etc., as well as aircraft and vehicle maintenance personnel. 
     The major components or assemblies housed within or forming part of the elongated housing include an end cap  426 , a side over lens  428 , an illumination module or light emitting assembly  430 , the battery pack  432 , a positive battery contact  434 , and a negative battery contact  436 . The end cap  426 , molded from the same material as the elongated shells, may be threaded to permit access to the battery pack  432  for replacement. The side lens  428  (See also side lens  24  in  FIG. 1 ) is a one-piece, transparent covering lens that extends the housing shell over the light emitting assembly  430 . The side lens  428  protects the LED/lens assemblies in the flood light array and includes an extension  428 A to protect the spot light array portions of the PLD  10 . In standard applications the side lens  428  may be “water clear,” a term denoting a high degree of colorless optical clarity. In certain applications, the side lens  428  may be colored, but preferably maintaining a high degree of optical clarity and light transmission. 
     The side lens  428  and its extension  428 A may be molded as a single piece of a suitable thermoplastic such as polycarbonate (PC), which exhibits a suitable blend of toughness, optical clarity, stability, etc. The side lens  428  is slightly curved in the illustrative embodiment to match the slight curvature of the second housing shell  424  over the first array of LEDs in the light emitting assembly  430 . The side lens extension  428 A may be formed as an end cap over the end of the PLD  10  including the spot light array. Further, the polycarbonate material satisfies a requirement that the refractive index of the side lens  428  be uniform throughout the side lens  428  to minimize distortion of the light beams emitted by the light emitting assemblies. An additional feature of the side lens  428  may be a gasket portion provided during an overmolding process that is well-known to persons skilled in the art. The gasket is a band of suitable material added along the edges of the side lens  428  where the side lens  428  mates with corresponding edges in the first  422  and second  424  elongated shells of the elongated housing. The gasket is formed in a mold similar to that used to form the side lens but having a different profile for being molded during a second operation (i.e., a “second shot”) before ejection of the finished part. The same technique may also be used to advantage during the molding of the first  422  and second  424  elongated shells. The overmold type of gasket ensures sealing against water and stability of the joint between the components of the elongated housing. 
     Continuing with  FIG. 7 , the light emitting assembly  430 , to be described in detail with  FIGS. 8A through 8D , includes a frame, a circuit board for the electrical circuit  160 , the lens/LED assemblies for the first  192  and second  202  arrays of LEDs, the first  222  and second  232  ON/OFF switches, and lens bezels (to be described) in a compact, rugged, serviceable unit that is configured for ease of replacement in the field. In  FIG. 7 , the first  222  and second  232  ON/OFF switches are represented by the flexible sealing bezel  502  having first and second raised portions  484  and  486  respectively covering the push buttons  504  and  506  of the first  222  and second  232  ON/OFF switches. The first  484  and second  486  raised portions, when the light emitting assembly  430  is assembled in position within the first  422  and second  424  halves of the elongated housing  420 , extend through the first  485  and second  487  openings in the first half  422  of the elongated housing. This arrangement of the first  222  and second  232  ON/OFF switches in the elongated housing  420  enables holding the PLD  10  in one hand with two of the fingers of the user&#39;s hand curled loosely around the body of the PLD  10  in the location of the switches  222 ,  232 , thus permitting easy, independent operation of either switch. The positive  434  and negative  436  battery contacts are preferably formed from a beryllium copper alloy well known for its properties as used in the manufacture of springs and contacts that require high longevity for uses involving many flexing cycles. 
     Referring to  FIG. 8A , there is illustrated a perspective view of a rearward side of a light emitting module  430  for use in the embodiment of  FIG. 1 . The light emitting module  430  is shown in various views in  FIGS. 8A ,  8 B and  8 D.  FIG. 8C  to be described later illustrates an internal portion of the structure of the light emitting module  430 . Reference numbers used in common in the several views identify features in the view that appear in one or more of the other views. In  FIG. 8A , a heat sink  440  disposed in the middle portion of the light emitting module  430  serves as a frame having first  452  and second  462  opposite sides for the support of the other structures that comprise the light emitting module  430 . In the description that follows, the terms heat sink and frame may be used interchangeably, accompanied by the same reference number  440 . The heat sink  440  is preferably fabricated of aluminum or other suitable conductor of heat. Further, the heat sink  440  is configured as a low profile platform for mounting thereon one or more arrays of light source units such as the lens/LED assembly  155  (Illustrated in  FIG. 4C ) combinations as described herein. The lens/LED assemblies  155  as they appear in the light emitting module  430  are most clearly shown in  FIG. 8C , described herein below. 
     Continuing with  FIG. 8A , the heat sink  440  preferably includes sufficient surface area for dissipating the heat generated by the LEDs in the first  192  and second  202  arrays of LEDs and the electrical circuit  160 . In the illustrated embodiment, the heat sink  440  includes a plurality of heat radiating fins  522  on the second (upward) side  462  as it appears in  FIG. 8A . A heat sink extension  470  is attached to the right-hand or first end  524  (as shown in the figure) of the light emitting module  430 , mounted at a right angle to the first end  524  of the frame  440 . The heat sink extension  470  may be a separate part attached with screws or other fastener or it may be fabricated with the frame  440  as a single piece heat sink unit. The heat sink extension  470  is provided to dissipate heat produced by the second array  202  of LEDs when producing a spotlight beam. The heat sink extension also supports the second array  202  of LEDs in the light emitting module  430 . 
     The heat sink or frame  440  shown in  FIG. 8A  further supports the printed circuit board (PC board)  442 , which contains the electrical circuitry  160 , adjacent the second side  462  of the heat sink or frame  440 . A first end (obscured by the heat sink extension  470 ) of the PC board  442  is attached to the heat sink extension  470 , preferably in a groove machined therein for the purpose or its equivalent. The second end  438  of the PC board  442  is supported by a spacer  512  that is positioned between the heat sink  440  and the PC board  442  and secured by a machine screw  478 . The spacer  512  is located in a recess in the second side  462  of the heat sink  440  that includes the heat radiating fins  522 . The PC board  442  may be supported on the frame  440  by other methods well known to persons skilled in the art or otherwise integrated into an assembly of the frame/heat sink  440  and the one or more arrays of light source units. 
     Mounted on the opposite side of the heat sink or frame  440  from the PC board  442  of the illustrative embodiment are the four lens/LED assemblies  155  (See  FIG. 4C ) of the first array  192  of LEDs. Partly visible in  FIG. 8A , between the heat sink  440  and a first array bezel  468  (to be described; see also the bezel  20  in  FIG. 1 ) are the outer sides of the lenses  454 ,  456 ,  458 , and  460  for the four lens/LED assemblies  155 . The first array bezel  468  is preferably a one piece molded thermoplastic component that serves as a front panel—a mask and alignment support surrounding the light-emitting side of the lenses  454 ,  456 ,  458 , and  460 . The first array bezel  468  also serves as a U-shaped mounting clip (when viewed in cross section) that holds the lens/LED assemblies  155  against the heat sink frame  440 . Extending from both of the longer, opposite edges of the first array bezel  468  are a plurality of resilient prongs or “flex arms”—a hooked end preferably having a curled “finger” (not shown) formed in the end of each prong. Two prongs  494 ,  496  of the three prongs disposed on the near side of the first array bezel  468  are shown in  FIG. 8A . Three such prongs  494  or  496  may be used on each side of the first array bezel  468 . The space within the curled “fingers” of the end of each prong  494 ,  496  snaps over the proximate edge of corresponding recessed notches  490 ,  492  formed in the edges of the heat sink or frame  440 . When installed on the frame  440 , the bezel  468  traps the individual lens/LED assemblies  155  between it and the frame  440  to secure them in position. 
     Two other assemblies are shown in  FIG. 8A . Mounted on the heat sink extension  470  is the second LED array  202  enclosed within a cannister  472 . The cannister  472  acts as a holder for the lens/LED assembly  155  of the second LED array  202 , positioning a heat transferring face of a printed circuit portion  474  of the lens/LED assembly  155  against the heat sink extension  470  in a correct alignment. The heat transferring face of the printed circuit portion  474  is typically an aluminum plate that is laminated to the surface of the printed circuit. The assembly of the cannister  472  and the printed circuit portion  474  of the lens/LED assembly  155  of the second array  202  is held in place by a front lens support  476  (which may also be called a second array bezel  476 ). The front lens support  476  has a lip that fits over a corresponding ridge formed in the first array bezel  468 . Once the lip is engaged with the ridge, the front lens support  476  may be tilted toward the heat sink extension  470  until a resilient prong  540  having a hooked end  546  hooks through an edge of a hole formed in the heat sink extension  470 , as shown in cross section in  FIG. 8D . Also shown in  FIG. 8A  is the forward surface of the second LED array  202 . Close observers will note that the side lens  428  and its extension  428 A (Reference number  24  in  FIGS. 1 and 2 ) are not shown in  FIG. 8A . In the illustrated embodiment the clear side lens  24  and the clear top lens  28  are shown as a single part, called the side lens  428  and its extension  428 A respectively in  FIG. 7 . 
     The remaining assembly of  FIG. 8A  includes a switch bracket  480 , which encloses and aligns the first  222  and second  232  ON/OFF switches (See  FIGS. 5 and 6A ) in position with respect to the frame  440 . The switch bracket  480  may be fabricated from, e.g., 19 gauge metal (approximately 0.042 in or 1.06 mm thick). A portion  488  of the second ON/OFF switch  232  is visible in  FIG. 8A . The ON/OFF switches  222 ,  232  are mounted on the frame  440 , the switch bracket  480  is slipped over the push button actuators  504 ,  506  (see  FIG. 8D ) of the switches  222 ,  232 , and a flexible sealing bezel  502  (also called flexible bezel) is placed over the push button actuators of the switches  222 ,  232 . The flexible bezel  502  has raised portions  484 ,  486  respectively for enclosing the push button actuators for the switches  222 ,  232 . A link  482  couples the raised portions  484 ,  486  of the flexible bezel  502  together. The link  482  helps to maintain alignment of the raised portions  484 ,  486  upon installation within the elongated housing  420 . The flexible bezel  502 , which may be fabricated of neoprene or similar material, is provided to seal the ON/OFF switches  222 ,  232  against intrusion of moisture, dirt, and other possible contaminants encountered during use of the PLD  10 . Wire leads (not shown in  FIGS. 8A through 8D  for clarity) may be provided for connecting the ON/OFF switches (obscured by the flexible bezel  502 ) to the electrical circuitry of the PC board  442 . 
     Referring to  FIG. 8B , there is illustrated a perspective view of the forward side of the light emitting module  430  illustrated in  FIG. 8A . The forward side of the light emitting module  430  is the side that faces in the direction of light emission. For example, see  FIG. 8C , which illustrates a forward axis  508  of illumination normal to the frame  440 . While shown disposed in a central portion of the frame  440 , the forward axis  508  may be defined at the optical axis of each light emitting assembly where it provides a reference for the angular orientation of the individual light emitting assembly (lens/LED assembly  155 ). As described previously with  FIG. 2 , and as will be described further herein below, the angular orientation of the light emitting assemblies is an aspect of one of the novel features of the present invention. While shown as defined for a frame  440  configured as a flat planar surface, where all normal reference lines are by definition parallel to each other, in other embodiments having a curved frame, the normal lines are unique to the location of each light emitting assembly. In such cases, the forward axis  508  would be a nominal axis defining the direction of illumination but not normal to all parts of the frame. 
     Continuing with  FIG. 8B , the perspective view is similar to the view in  FIG. 8A  except that the light emitting module  430  has been rotated about its longitudinal axis 180°, thereby exposing the forward, light emitting side the light emitting module  430 . Each of the lenses  454 ,  456 ,  458 , and  460  for the four lens/LED assemblies  155  of the illustrated embodiment are shown in alignment with the first array bezel  468 . Also shown are two of the resilient prongs  494 ,  496  extending from the first array bezel  468  that engage two corresponding notches  490 ,  492  in the edges of the frame/heat sink  440  to secure the lens/LED assemblies  155  against the frame  440 . Four other prong/latch combinations are used (but not shown) to secure the first array bezel  468  to the frame  440  to entrap and secure the four lens/LED assemblies  155  there between. The PC board  442  is shown disposed below the frame  440 , adjacent the second side  462  of the frame  440 . 
     The partly obscured first ends of the heat sink or frame  440  and the PC board  442  are disposed toward the heat sink extension  470 . The second end  438  of the PC board  442  is shown oriented to the left in the figure toward the first and second ON/OFF switches  504 ,  506  (not visible in  FIG. 8B , but see  FIG. 8D ) and enclosed within the corresponding raised portions  484 ,  486  of the flexible bezel  502 . Wire leads (not shown) for connecting the switches  504 ,  506  to the PC board  442  are typically routed alongside the bodies of the switches  504 ,  506 . The switch bracket  480  is shown extending from beneath the flexible bezel  502  and upward along each side of the first array bezel  468 . The front lens support  476  and the forward surface of the lens  26  of the second LED array  202  are shown attached to the right-hand end of the light emitting module  430  in  FIG. 8B . 
     Referring to  FIG. 8C , there is illustrated a perspective view of a basic module  500  of the light emitting module  430  appearing in  FIG. 8B . In fact, reduced to the minimum essentials, the basic module  500  embodies many of the essential features of several aspects of the present invention. The heat sink or frame  440  is shown, having the first side  452  and the second side  462 , as well as the first end  524 . The PC board  442 , having a second end  438 , is shown just below the frame  440 . Not visible in the view of  FIG. 8C  (But, see  FIG. 8D ) is the spacer  512  between the PC board  442  and the frame  440  within which the machine screw  478  passes to secure these two structures together. Also shown mounted on the first side  452  of the frame  440  are four lens/LED assemblies  155 , identified respectively by their associated lenses  454 ,  456 ,  458 , and  460 . Each assembly occupies a respective recess  444 ,  446 ,  448 , and  450  machined into the first side  452  of the frame  440 . The bottom surface of each of the recesses  444 ,  446 ,  448 , and  450  is machined at an angle relative to the normal axis  508  that is somewhat less than 90° so that the optical axis of the lens/LED assembly  155  installed therein is tilted in a predetermined direction by the amount of the previously described angle θ. 
     Each lens/LED assembly  155  shown in  FIG. 8C  includes its lens  454 ,  456 ,  458 , and  460  (each lens being configured like the lens  100  in  FIGS. 4A ,  4 B, and  4 C). Thus, each of the lens/LED assemblies  155  of  FIG. 8C  includes a base  142 , a substrate  144 , and the concave light emitting surface  110  of the lens  100  having the plurality of concentric annular rings  120  formed thereon as in the  FIGS. 4A ,  4 B, and  4 C. Close observation of the placement of the individual lens/LED assemblies  155  reveals that each is canted at substantially the same (generally small) angle θ with respect to the normal axis of each lens/LED assembly  155  but in a different azimuthal direction with respect to the frame  440  and its normal or forward axis  508  (See  FIG. 8D ). This relationship will be described in detail with  FIG. 8D  to follow. 
     The basic module  500  illustrated in  FIG. 8C  is constructed as a rugged assembly of the essential components of the light emitting module  430 . All of the components are solid structures fabricated of solid materials that are very resistant to breakage, particularly when secured in place by the front bezel  468  and installed within the elongated housing  12  as shown in  FIG. 7 . The elongated housing is also constructed of materials highly resistant to damage from impact and other mechanical hazards, as well as extreme environmental, chemical, and electrical conditions. When assembled together, the components of the PLD  10  as described herein are designed to withstand heavy use and abusive handling as is often encountered in industrial, security, military, and public safety applications. Other techniques or modifications such as use of silicone sealants, potting compounds, and the like may be used to provide enhanced protection from the effects of moisture intrusion or contact with harsh chemical or environmental conditions. 
     Referring to  FIG. 8D , there is illustrated a side cross section view of the light emitting module  430  of the embodiment of  FIG. 8B , taken generally along the longitudinal centerline or axis  14  and with the switch bracket  480  removed. In this view, the forward axis  508  that is defined normal to the first side  452  of the heat sink or frame  440  is shown oriented upward in the drawing and placed at the location of the machine screw  478  and spacer  512  securing the PC board  442  to the frame  440 . The individual lens/LED assemblies  155  (associated with their respective lenses  454 ,  456 ,  458 , and  460 ) are shown installed in their respective recesses  514 ,  516 ,  518 , and  520 . In practice, a very thin layer of thermally conductive, double-sided tape (not shown) or other thermal compound of the type well-known to persons skilled in the art may be placed in the interface between each LED/lens assembly and the recess in the heat sink/frame  440 . 
     Of particular interest in this view in  FIG. 8D  is the orientation of the individual lens/LED assemblies  155  in their respective recesses as shown in cross section  514 ,  516 ,  518 , and  520 . Each of the recesses  514 ,  516 ,  518 , and  520 , and correspondingly the lens/LED assembly  155  installed therein, is tilted in a different azimuthal direction relative to the forward axis  508  of the first side  452  of the heat sink or frame  440 . The lens/LED assembly  155  for the lens  454  installed in the recess  514  is shown tilted to the right in  FIG. 8D  by a predetermined angle of approximately 5°. That is, the approximate angle between the optical axis of the lens/LED assembly  155  for the lens  454  and a normal line passing through the LED at the plane of the frame  440  is approximately 5°. Similarly, the lens/LED assembly  155  for the lens  456  installed in the recess  516  is shown tilted into the plane of the drawing (i.e., away from the viewer) in  FIG. 8D  by a predetermined angle of approximately 5°. Further, the lens/LED assembly  155  for the lens  458  installed in the recess  518  is shown tilted out of the plane of the drawing (i.e., toward the viewer) in  FIG. 8D  by a predetermined angle of approximately 5°. Finally, the lens/LED assembly  155  for the lens  460  installed in the recess  520  is shown tilted to the left in  FIG. 8D  by a predetermined angle of approximately 5°. One can visualize the light emitting assembly  430  from a point directly above the forward axis  508 , looking downward toward the assembly  430 , wherein the optical axes of the four lens/LED assemblies  155  are tilted away from each other at 90° intervals relative to the position of the forward axis  508 , substantially mimicking the four points of the compass, N, W, S, and E (for North, West, South, and East). This arrangement provides the projected flood light beam pattern as illustrated in  FIG. 3  described herein above. 
     In the illustrated embodiment of the PLD  10 , the predetermined angles of the optical axes of the individual lens/LED assemblies  155  is fixed at approximately 5° from the normal, i.e., from an axis parallel to the forward axis  508 . As indicated previously, depending upon the beam width characteristics, number of light emitting assemblies, etc., the “predetermined angle” may vary. The range of variation may typically be within approximately +/−3° of the nominal 5° angle described for the illustrated embodiment. This range, it will be appreciated allows for a wide variation in the beam width characteristic in accordance with the one quarter beam width index also described herein above. In other embodiments, larger “predetermined angles,” for example up to 15° may be employed to achieve particular illumination results. Moreover, while in most cases the predetermined angle is a non-zero angle, in some embodiments, at least one of the light emitting assemblies may be oriented with respect to the reference forward direction at a predetermined angle of zero degrees. Further, in other alternate embodiments, the angles of the optical axes may be varied or adjusted to provide a particular illumination characteristic. It is even possible, with suitable structural revisions apparent to persons skilled in the art, to provide for an adjustable flood light pattern by configuring the structure of the light emitting module  430  to vary the angles of the optical axes of the individual lens/LED assemblies  155 . 
     Continuing with  FIG. 8D , the fifth lens/LED assembly  157  will be described. The fifth assembly  157  may be identical with the lens/LED assembly  155  previously described with respect to  FIG. 4C . However, the fifth lens/LED assembly  157 , which may utilize a different lens or include an LED having a different operating power level to provide a spot light beam, is otherwise very similar to the lens/LED assembly  155 . As before, the four individual forward (for the flood light beam) lens/LED assemblies  155  include the LED (actually inside the hemispherical dome  550 ) mounted on each base  510 . The assembly thus includes the LED  510 , the substrate  144  and the lens itself  454 ,  456 ,  458 , or  460 . 
     Joining the right-hand end  524  of the heat sink or frame  440  in  FIG. 8D  is the heat sink extension  470 . Supported on the heat sink extension  470  is a fifth top (for the spot light beam) lens/LED assembly  157  (including the elements  530 ,  474 , and  26 ) mounted within a cannister  472 . The cannister  472  is supported directly against the PC board substrate  474  of the top lens/LED assembly  157  as held in place by the front lens support  476  acting in cooperation with the first array bezel  468  as previously described with  FIG. 8A . The front lens support  476  has a lip that fits over a corresponding ridge formed in the first array bezel  468 . Once the lip is engaged with the ridge, the front lens support  476  may be tilted toward the heat sink extension  470  until a resilient prong  540  having a hooked end  546  hooks through an edge of a hole formed in the heat sink extension  470 , as shown in cross section in  FIG. 8D . 
       FIG. 8D  includes additional detail of the first  222  and second  232  ON/OFF switches, shown in their correct location but with the switch bracket  480  removed for clarity. The first switch  222 , having a push button actuator  504 , is shown enclosed within the cover  484  portion of the flexible sealing bezel  502 . Similarly, the second switch  232 , having a push button actuator  506 , is shown enclosed within the cover  486  portion of the flexible sealing bezel  502 . The first  222  and second  232  switches are mounted against a flat surface formed into the second side  462  of the heat sink or frame  440 . Other structures shown in  FIG. 8D  have been previously described. 
     To summarize several of the features of the light emitting module of the illustrative embodiment of the present invention, an array of a plurality of compact light emitting assemblies is mounted on a frame configured as a heat sink. The frame serves the dual purpose of providing a structural platform and a thermal management component. The frame further provides features that ensures proper alignment of the light emitting devices wherein each light emitting assembly is preferably but not necessarily disposed at a non-zero predetermined angle relative to a forward axis normal to and defined at the location of the light emitting assembly. The predetermined angle is selected to aim the individual light emitting assemblies in a direction that provides a predetermined overlap of individual light beams of a given beam width preferably resulting in a uniform, high brightness pattern on a target surface. The source of current connected to the light emitting devices, as may be implemented on a printed circuit board, is also mounted on the frame, conveniently but not necessarily on the side of the frame opposite the light emitting assemblies. The compact light emitting module that is thus provided is readily adaptable to a variety of compact, high performance lighting product configurations. 
     Several aspects of the features of the optical system of the illustrative embodiment of the present invention include a unitary lens and light emitting device combination that produces a highly uniform beam of light, corrected for distortions and gaps in illumination, throughout a full beam width angle in the range of 40°+/−10°. This lens/LED combination or light source unit is adaptable for use principally in arrays of such light source units to provide optimum flood illumination from a portable, hand held task lamp product. The unitary lens is formed as a solid body lens which incorporates all of the necessary optical surfaces in a single piece unit, including the pattern-correcting spherical refracting surface, concave in the forward direction of illumination, that smooths out intensity variations in the overall illumination pattern. The light source unit provided by this lens/LED combination may be arranged in many different arrays formed of a plurality of such light source units for use in a wide variety of applications. 
     Several aspects of the features of the electrical circuit of the illustrative embodiment of the present invention include a single drive circuit that is configured to drive disparate current loads of first and second lighting arrays—combinations of compact light emitting devices—with the respective regulated constant currents. Further, a configuration of first and second standard push ON, push OFF, latching switches provides independent control of the two lighting loads wherein each switch operates in three states including momentary ON, continuous ON, and OFF. The circuit is readily adapted to providing continuous or pulsed drive to the lighting arrays. Also described are optional circuit features that provide a dimming control, a strobe control, and a low battery indicator. 
     Another aspect of the electric circuit utilizes a single pole, single throw switch having normally open contacts in a conductive path in a non-intuitive manner to sequentially provide three operable states including latched engagement (path closed, circuit OFF), momentary disengagement (path opened, circuit ON momentarily), and latched disengagement (path open, circuit ON until switch actuated). 
     All of the features summarized in the preceding paragraphs may be combined in a single combination task lamp and flashlight, providing a flood light having a uniform, high brightness beam pattern and a spot light having a narrower, more focused beam pattern, each type of beam independently controlled in a three-state sequence by simple push button switches. The two kinds of light beams are produced by separate arrays of compact light emitting devices, which are both driven by a single electrical circuit that provides disparate, regulated constant currents to the respective LEDs. The optics and electronics are constructed in a single, ruggedized, compact module, and the module enclosed within a slim, rugged housing and easily field replaceable with minimal tools. 
     While the invention has been shown and described with particularity in only one of its forms to illustrate the principles of the invention, the invention is not thus limited to the representative embodiment but is susceptible to various changes and modifications that may occur to persons skilled in the art in applying the invention to certain circumstances without departing from the scope of the appended claims. For example, while specific dimensions, angles, materials and processes are described for the representative embodiment, the invention is not limited to the specific example but allows substantial variation of structural features and processes within the range of equivalents that may occur to persons practicing the invention. Further, the numbers and arrangement of the LEDs may be altered, or the power levels changed to provide particular lighting performance. The colors of the LED emitters may be varied. The color of the lens unit or assembly or of the over lens may be varied or made interchangeable for specific purposes. The overall shape of the housing for the lamp may be varied to suit particular embodiments such as lanterns, area lighting, etc.