Circuit for illuminating multiple light emitting devices Number:7,402,961 from the United States Patent and Trademark Office (PTO) owispatent

Title: Circuit for illuminating multiple light emitting devices

Abstract: A single drive circuit is configured to drive disparate current loads of first and second combinations of compact light emitting devices with respective regulated constant currents. Standard push ON, push OFF latching switches provide 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. Circuits for dimming control, strobe control, and a low battery indicator are also described.

Patent Number: 7,402,961 Issued on 07/22/2008 to Bayat,   et al.

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Inventors:	Bayat; Bijan (Plano, TX), Newton; James (Arlington, TX), Ellis; Robert Lee (Midlothian, TX)
Assignee:	Bayco Products, Ltd. (Wylie, TX)
Appl. No.:	11/329,338
Filed:	January 10, 2006

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Current U.S. Class:	315/295 ; 315/313
Current International Class:	H05B 37/02 (20060101)
Field of Search:	315/51,129,130,131,136,291,294,295,312,313,314,362 307/139,143

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References Cited [Referenced By]

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U.S. Patent Documents

3784844	January 1974	McGrogan, Jr.
3944854	March 1976	Keller
6118259	September 2000	Bucks et al.
6161910	December 2000	Reisenauer et al.
6836081	December 2004	Swanson et al.
2004/0095185	May 2004	Bucks et al.
2004/0130518	July 2004	De Krijger et al.
2004/0145320	July 2004	Nijhof et al.
2005/0018435	January 2005	Selkee et al.

Primary Examiner: Tran; Thuy Vinh
Attorney, Agent or Firm: Whitaker, Chalk, Swindle & Sawyer, LLP Mosher; Stephen S.

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Claims

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What is claimed is:

1. 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.

2. The circuit of claim 1, wherein the current selector comprises: individual first and second ON/OFF switches for respectively selecting delivery of current to the first and second arrays of LEDs.

3. The circuit of claim 2, wherein the current selector comprises: a control signal output for enabling current flow in at least one of the first and second array of LEDs in response to activation of a corresponding ON/OFF switch.

4. The circuit of claim 2, wherein the current selector comprises: a semiconductor switch circuit, connected in series with a current supply line from the DC supply, that is controlled by activation of one of the first and second ON/OFF switches.

5. The circuit of claim 4, wherein the semiconductor switch circuit is alternately enabled and inhibited at a predetermined rate by a strobe signal applied to an input of the current selector.

6. The circuit of claim 5, wherein the predetermined rate corresponds to the frequency of a gated oscillator providing the strobe signal applied to the input of the current selector.

7. The circuit of claim 1, wherein the switching regulator circuit comprises: means for regulating different constant first and second drive current levels in each first and second arrays of LEDs.

8. The circuit of claim 7, wherein the switching regulator comprises: a flyback converter circuit; a self-oscillating PWM driver circuit coupled to an input of the flyback converter circuit for regulating the constant first and second drive current levels to the first and second arrays of LEDs in response to a feedback voltage proportional to a load current change in the first and second LED arrays; and a current sense network comprising at least one resistor in common to the first and second drive currents in the respective first and the second array of LEDs, for providing the feedback voltage.

9. The circuit of claim 1, wherein the second array of LEDs is configured to inhibit the flow of current in the first array of LEDs when the second array of LEDs is conducting current.

10. The circuit of claim 9, wherein conduction of current in the second array of LEDs is independently enabled by the current selector circuit when a corresponding second ON/OFF switch configured to control the second array of LEDs is placed in a state for causing illumination of the second array of LEDs.

11. The circuit of claim 9, wherein the second array of LEDs is configured to have a voltage drop across it during the duration of time it is conducting current that is substantially less than the voltage drop across the first array of LEDs required for the first array of LEDs to become illuminated, thereby inhibiting conduction of current in the first array of LEDs.

12. The circuit of claim 1, wherein the first array of LEDs comprises: a plurality of LEDs connected in series, wherein all of the LEDs are configured for operating at approximately the same value of current.

13. The circuit of claim 1, wherein the second array of LEDs comprises at least one LED.

14. The circuit of claim 1, wherein the first and second arrays of LEDs each includes at least one LED.

15. The circuit of claim 1, wherein each LED is a light emitting diode.

16. The circuit of claim 1, wherein the current selector circuit comprises: a first single pole single throw (SPST) switch having normally open (NO) contacts for selecting current to be delivered to the first array of LEDs; and a second SPST switch having NO contacts for selecting current to be delivered to the second array of LEDs.

17. The circuit of claim 16, wherein the array of LEDs controlled by its respective switch is OFF when the respective switch is in a contacts-engaged condition, and no current is drawn from the DC supply.

18. The circuit of claim 16, wherein the first and second switches are each set independently to a contacts-engaged state when no current is selected from the DC supply and the respective first and second arrays of LEDs are turned OFF.

19. The circuit of claim 16, wherein the first and second switches are set independently to a contacts-disengaged state when current is selected from the DC supply and the respective first and second arrays of LEDs are turned ON.

20. The circuit of claim 16, wherein the first and second switches include an indexing mechanism operated by an actuator for latching the NO contacts in an engaged state wherein the contacts are closed, and in a disengaged state wherein the contacts are opened.

21. The circuit of claim 20, wherein the first and second switches each provide a momentary ON state of the respective first and second arrays when a first or second switch is operated by a predetermined partial pressure exerted on the actuator that is insufficient to step the indexing mechanism into a latched, open-contact condition from an OFF state wherein the respective contacts are in a closed condition.

22. The circuit of claim 1, further comprising: a circuit housing that includes space for the circuit, the DC supply, the first and second arrays of LEDs, a first SPST switch for operating the first array of LEDs and a second SPST switch for operating the second LED array.

23. The circuit of claim 22, wherein: the circuit housing is configured as a portable handheld lighting device.

24. The circuit of claim 22, wherein: the circuit housing is configured as a stationary lighting device.

25. The circuit of claim 24, further comprising: a switch housing configured to be remotely located from the circuit housing, the switch housing containing the first and second SPST switches.

26. The circuit of claim 1, wherein the DC supply comprises: at least one battery cell.

27. The circuit of claim 1, wherein the DC supply comprises: a converter circuit for converting an AC supply voltage to a DC supply voltage.

28. The circuit of claim 1, further comprising a strobe circuit coupled from an output thereof to an input of the current selector circuit for gating the current selector at a predetermined strobe rate.

29. The circuit of claim 1, further comprising: a dimming circuit coupled to the sense input of the switching regulator for selectively modifying the voltage present at the sense input.

30. The circuit of claim 29, wherein the dimming circuit causes a reduction in the voltage generated by the common current sense device in proportion to the desired dimming of the light output of the first array and the second array of LEDs.

31. The circuit of claim 1, further comprising: a low battery indicator having an input responsive to a DC supply voltage present in the circuit and having an output coupled to a visual indicator.

32. The circuit of claim 31, wherein the low battery indicator further comprises: a comparator circuit for activating the visual indicator when the DC supply voltage drops below a predetermined threshold.

33. The circuit of claim 32, wherein the predetermined threshold corresponds to a remaining operational life of the DC supply of approximately one hour.

34. In a circuit for illuminating multiple light emitting devices, a combination 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 be supplied to each of a first array and a second array of the multiple light emitting devices (LEDs); a first single pole single throw (SPST) switch having normally open (NO) contacts for selecting current to be delivered to the first array of LEDs; and a second SPST switch having NO contacts for selecting current to be delivered to the second array of LEDs.

35. The circuit of claim 34, wherein the first and second SPST switches are each set independently to a contacts-engaged state when no current is selected from the DC supply and the respective first and second arrays of LEDs are turned OFF.

36. The circuit of claim 34, wherein the first and second SPST switches are set independently to a contacts-disengaged state when current is selected from the DC supply and the respective first and second arrays of LEDs are turned ON.

37. The circuit of claim 34, wherein the first and second SPST switches include an indexing mechanism operated by an actuator for latching the NO contacts in an engaged state wherein the contacts are closed, and in a disengaged state wherein the contacts are opened.

38. The circuit of claim 37, wherein the first and second SPST switches each provide a momentary ON state of the respective first and second arrays when a first or second switch is operated by a predetermined partial pressure exerted on the actuator that is insufficient to step the indexing mechanism into a latched, open-contact condition from an OFF state wherein the respective contacts are in a closed condition.

39. The circuit of claim 34, wherein the first and second SPST switches each provide a momentary ON state of the respective first and second arrays when a first or second SPST switch is operated by a predetermined partial pressure exerted on the actuator that, while insufficient to step the indexing mechanism into a latched, open-contact condition from an OFF state wherein the respective contacts are in a closed condition, is sufficient to provide a momentary ON state of the respective first and second arrays.

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Description

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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 5 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 FIG. 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 maybe 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 maybe 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, 4B, and 4C 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 E1, E2, E3, and E4) 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 .theta. with respect to a normal reference line (designated as N1, N2, N3, and N4) 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 .theta. will be described in further detail herein below.

Each of the light emitters E1, E2, E3, and E4 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 E1, E2, E3, and E4 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 .theta. with respect to the normal line defined for each of the light sources 22. The same angle .theta. 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 (N1), from the perspective of the PLD 10, at the angle indicated by the symbol .theta.. Similarly, optical axis 54 (the E2 axis) is defined to be oriented horizontally leftward relative to the normal line 64 (N2), from the perspective of the PLD 10, at the angle indicated by the symbol .theta.. Similarly, optical axis 56 (the E3 axis) is defined to be oriented horizontally rightward relative to the normal line 66 (N3), from the perspective of the PLD 10, at the angle indicated by the symbol .theta.. Likewise, optical axis 58 (the E4 axis) is defined to be oriented vertically downward relative to the normal line 68 (N4), from the perspective of the PLD 10, at the angle indicated by the symbol .theta.. Thus, each of the light sources 22 is oriented or aimed at the angle .theta. 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 .theta.. 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 .theta. of approximately 5 degrees (5.degree.), wherein each light emitting assembly provides a beam of light having a beam width angle of approximately 40 degrees (40.degree.), 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 .theta., which in the illustrated embodiment is 2.times.5.degree.=10.degree.. 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.degree.) and the beam width angle of the individual light emitting assemblies in the array (here 40.degree.) 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 .theta.. 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.degree. 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 E1 diverges northward, E2 diverges westward, E3 diverges southward, and E4 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 .theta. is a non-zero angle typically less than approximately ten degrees (10.degree.). In the preferred embodiment, .theta. is approximately 5.degree.. 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 .theta. is dependent on the design of the lens assembly, particularly the factors of the lens assembly that affect the angle .beta. of the beam width. The beam width angle .beta. 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 .beta., the optical axis divergence angle .theta., 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 maybe 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 E1 having an optical axis 52 provides a projected beam cross section or pattern 82. Similarly, light emitter E2 having an optical axis 54 provides a projected beam cross section or pattern 84. Similarly, light emitter E3 having an optical axis 56 provides a projected beam cross section or pattern 86. Likewise, light emitter E4 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.degree. 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.degree. F. to +270.degree. F., as compared to acrylic having an upper temperature limit of approximately 160.degree. 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 .beta.. In the preferred embodiment, the beam angle .beta. is approximately 40.degree.. 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.degree.+/-5.degree.. This angle is often called the "half angle" of the beam, denoted herein by the Greek letter .alpha.. The beam angle denoted by .beta. is thus equivalent to two times the half angle .alpha.. 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.sub.1x+b.sub.2x.sup.2+b.sub.3x.sup.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 .alpha.--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 .beta.) of the reference cone.

The critical angle .alpha., 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 .alpha. 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 .alpha. 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 .alpha. 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 .alpha. 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 .beta.. 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 .alpha..

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.RTM. 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.RTM. 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 ex