Patent Publication Number: US-9408262-B2

Title: Multi-mode portable lighting device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of U.S. patent application Ser. No. 13/007,981, filed on Jan. 17, 2011, which is a continuation-in-part, and is based on and claims priority to U.S. patent application Ser. No. 12/353,396, filed Jan. 14, 2009, now U.S. Pat. No. 8,169,165, the disclosure of which is incorporated by reference as if fully set forth herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to portable lighting devices, including, for example, flashlights, lanterns and head lamps, and their circuitry. 
     BACKGROUND 
     Various handheld or portable lighting devices, including flashlights, are known in the art. Such lighting devices typically include one or more dry cell batteries having positive and negative electrodes. The batteries are arranged electrically in series or parallel in a battery compartment or housing. The battery compartment is also sometimes used to hold the lighting device, particularly in the case of flashlights. An electrical circuit is established from a battery electrode through conductive means which are electrically coupled with an electrode of a light source, such as a lamp bulb or a light emitting diode (“LED”). After passing through the light source, the electric circuit continues through a second electrode of the light source in electrical contact with conductive means, which in turn are in electrical contact with the other electrode of a battery. The circuit includes a switch to open or close the circuit. Actuation of the switch to close the electrical circuit enables current to pass through the lamp bulb, LED, or other light source—and through the filament, in the case of an incandescent lamp bulb—thereby generating light. 
     Flashlights and other portable lighting devices have conventionally employed a mechanical power switch in the main power circuit of the flashlight to turn “on” the flashlight and turn “off” the flashlight. When the user desired to turn “on” the flashlight, the user manipulated the mechanical power switch to mechanically connect two contacts to close the switch and complete the power circuit, thereby allowing current to flow from the positive terminal of the batteries, through the light source, and back to the negative terminal of the batteries. When the user desired to turn “off” the flashlight, the user manipulated the mechanical switch to disconnect the two contacts of the switch and thereby open the switch and break the power circuit. The mechanical switch in such devices, therefore, acts as a conductor in completing the power circuit and conducting current throughout the operation of the portable lighting device. 
     A variety of mechanical switch designs are known in the art, including, for example, push button switches, sliding switches, and rotating head switches. Such switches tend to be fairly intuitive and easy to operate by the user. However, portable lighting devices having just a simple mechanical power switch do not include automated operating modes, such as, for example, a blink mode, a power reduction mode, or an SOS mode. To include such automated functionality in a portable lighting device, the portable lighting device must have advanced electronics. 
     For example, multi-mode electronic flashlights and other portable lighting devices have been designed using an electronic power switch controlled by a processor of a microchip or microcontroller. In such lighting devices, the various modes that are programmed into the microchip are selected through the appropriate manipulation of a user interface, such as a momentary switch. 
     In one approach, the electronics of the multi-mode portable lighting device remain constantly connected to the power source. As a result, however, the electronics constantly consume power, thereby decreasing the useful battery life, or in the case of rechargeable batteries, the operational time between charges. 
     In another approach, a mechanical power switch, which is disposed electrically in series with the light source and controller, is used to simultaneously break the circuit powering the electronics and the light source. As a result, the electronics do not consume power from the batteries (or battery) when the portable lighting device is turned off. However, in order for the mechanical power switch to be used as the user interface to select different modes of operation by, for example, opening and then closing the mechanical power switch within a defined period of time, the microchip is provided with an alternative source of temporary power. 
     The alternative source of temporary power is provided so that when the mechanical power switch is opened the microchip will remain temporarily powered, even though the portable lighting device has been shut off, until the mechanical power switch is again closed. In the absence of the alternative source of temporary power, the microchip would lose power when the mechanical power switch is opened, causing the controller to reset and return to its default mode of operation the next time the mechanical power switch is closed instead of toggling to the next operational mode. 
     One or more capacitors arranged in parallel with the controller have been used as the alternative source of power. The capacitors are selected to have sufficient capacitance to power the controller for a suitable period of time, such as one to two seconds, following the opening of the mechanical power switch before falling below the reset voltage of the controller. Thus, as long as the mechanical power switch is again closed within the allotted time frame, the lighting device will begin to operate in the next mode of operation. 
     A disadvantage of this approach is that significant capacitance is required to be able to power the controller for an adequate period of time, resulting in increased cost. In addition, in some configurations, the required capacitor(s) may have a physical footprint that is larger than the amount of space available on the printed circuit board to be included in the portable lighting device. 
     SUMMARY 
     An object of the present patent document is to provide a multi-mode portable lighting device that uses a mechanical power switch as the user interface and that addresses, or at least ameliorates, one or more of the problems associated with the multi-mode portable lighting devices discussed above. 
     Accordingly, in a first aspect, a multi-mode portable lighting device, such as a flashlight, with multiple modes of operation is provided. The portable lighting device is operated by a mechanical power switch. Actuation of this switch powers on and off the portable lighting device. It is also used to select the mode of operation. In one embodiment, there are no other switches, inputs, or any other man to machine interface other than the single mechanical power switch. At any time when the mechanical power switch is in the off (or open) position, all circuitry is physically disconnected from the battery and no battery current is consumed. The lighting device may include a number of modes of operation and the modes of operation may include, for example, a normal mode, one or more power save modes, a flash mode, an SOS mode, etc. 
     According to one embodiment, the multi-mode portable lighting device comprises a housing for receiving a portable power source having a positive electrode and a negative electrode, a light source having a first electrode and a second electrode, and a main power circuit for connecting the first and second electrodes of the light source to the positive and negative electrodes of the portable power source, respectively. The main power circuit includes a mechanical power switch and an electronic power switch disposed electrically in series with the light source. The portable lighting device further comprises a controller electrically coupled in series with the mechanical power switch so that when the mechanical power switch is opened, the controller is not powered by the portable power source. The controller includes an output for providing a control signal for controlling the opening and closing of the electronic power switch, and the controller is configured to control the electronic power switch in a manner to provide at least two modes of operation. A state machine having a memory mechanism for temporarily storing a mode of operation and at least one output coupled to the controller for communicating at least one output signal to the controller is also included in the portable lighting device. Further, the controller is configured to determine the mode of operation based on at least one output signal from the state machine at power up and then to write a new mode of operation to the state machine. 
     According to another aspect, a method of operating a multi-mode portable lighting device including a main power circuit for connecting a light source to a portable power source and a controller for controlling an electronic power switch disposed in the main power circuit which is in electrical series with the light source, wherein the controller is electrically connected in series to a mechanical power switch disposed in the main power circuit in series with the light source and which acts as the user interface to the controller. The method comprises the steps of: using the controller at power up to read at least one output signal from a state machine to determine a first mode of operation based on the at least one output signal; and writing a second mode of operation from the controller to the state machine following power up, wherein the state machine remembers the second mode of operation for a brief period after the mechanical power switch is opened so that if the mechanical power switch is closed before the brief period lapses, the controller will operate in the second mode of operation. Preferably, the brief period is long enough for a user to reliably open and close the mechanical power switch without undue difficulty. Typically a period of about 1.5 seconds should be adequate. 
     According to another aspect, a method of calibrating one or more memory capacitors of a driver circuit for a multi-mode portable lighting device is provided, wherein each memory capacitor is connected to a data port of a controller in parallel with a bleed off resistor. The method according to one embodiment comprises powering the driver circuit to charge each of the one or more memory capacitors, removing the power from the driver circuit for a predetermined time interval, powering the driver circuit as soon as the predetermined time interval has lapsed, and measuring the voltage value on each of the one or more memory capacitors; and storing the voltage measured for each of the one or more memory capacitors in a non-volatile memory accessible by the controller. 
     According to another aspect, a circuit is described whereby a microcontroller is powered by a regulating circuit. The regulating circuit may convert between a current regulating circuit and a voltage regulating circuit that may enable a light source, such an LED, to be turned off and on through pulse width modulation, while during the off cycle of the PWM signal, a microcontroller may still remain powered. 
     Further aspects, objects, desirable features, and advantages of the invention will be better understood from the following description considered in connection with accompanying drawings in which various embodiments of the disclosed invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a flashlight according to an embodiment of the present patent document. 
         FIG. 2  is a cross-sectional view of the flashlight of  FIG. 1  taken through the plane indicated by  2 - 2 . 
         FIG. 3  is an enlarged cross-sectional side view of the front end of the flashlight of  FIG. 1  as taken through the plane indicated by  2 - 2  where the flashlight is shown in the OFF position. 
         FIG. 4  is a cross-sectional view of the LED module of the flashlight of  FIG. 1 . 
         FIG. 5A  is a side view of a retaining collar, and  FIG. 5B  is a longitudinal cross-sectional view through the retaining collar. 
         FIG. 6  is an embodiment of a circuit diagram for the flashlight of  FIG. 1 . 
         FIG. 7  is a circuit diagram according to one embodiment of a state machine for the flashlight of  FIG. 1 . 
         FIG. 8  is another embodiment of a circuit diagram for the flashlight of  FIG. 1 . 
         FIG. 9  is a circuit diagram of one embodiment of a regulating circuit for use in the circuit of  FIG. 8 . 
         FIG. 10  is another embodiment of a circuit diagram for the flashlight of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     A multi-mode flashlight  10  according to an embodiment is illustrated in perspective in  FIG. 1 . The flashlight  10  incorporates a number of distinct aspects. While these distinct aspects have all been incorporated into the flashlight  10 , it is to be expressly understood that the invention is not restricted to flashlight  10  described herein. Rather, the inventive features of the flashlight  10  described below, both individually as well as in combination, all form a part of the invention. Further, as will become apparent to those skilled in the art after reviewing the present disclosure, one or more aspects of the present invention may also be incorporated into other portable lighting devices, including, for example, head lamps and lanterns. 
     Referring to  FIG. 1 , the flashlight  10  includes a head assembly  20 , a barrel  12 , and a tail cap assembly  30 . The head assembly  20  is disposed about the forward end of the barrel  12 . The tail cap assembly  30  encloses the aft end of the barrel  12 . 
       FIG. 2  is a cross-sectional view of the flashlight of  FIG. 1  taken through the plane indicated by  2 - 2 .  FIG. 3  is an enlarged cross-sectional side view of the front end of the flashlight of  FIG. 1  as taken through the plane indicated by  2 - 2 . The flashlight is shown in the OFF position in  FIGS. 2-3 . 
     Referring to  FIGS. 2 and 3 , a light source  14  is mounted to the forward end of the barrel  12 . In the present embodiment, the light source  14  is mounted so that it is disposed at the aft end of reflector  106 . In other embodiments, the reflector  106  may be omitted, or its shape changed. 
     The barrel  12  is a hollow, tubular structure suitable for housing a portable power source, such as, for example, one or more batteries  16 . Thus, the barrel  12  serves as a housing for receiving a portable power source having a positive and a negative electrode. 
     In the illustrative embodiment, barrel  12  is sized to accommodate two batteries  16  disposed in a series arrangement. The batteries are preferably alkaline type dry cell batteries of a AA size in the present embodiment. However, rechargeable batteries may be used instead of dry cell batteries. In addition, batteries having sizes other than AA may be used. 
     The barrel  12  may also be configured to include a single battery, three batteries, or a plurality of more than three batteries arranged in either a series or a side-by-side arrangement. Other suitable portable power sources, including, for example, high capacity storage capacitors, may also be used. 
     In the illustrated embodiment, the barrel  12  includes forward threads  18  formed on the outer diameter of its front end, and aft threads  22  formed on the inside diameter of its aft end. The barrel  12  of the present embodiment also includes an annular lip  24  of reduced diameter projecting from the inner diameter of the barrel at a forward end. An aft facing surface of the annular lip  24  forms a contact  21  for a mechanical power switch described below. 
     Referring to  FIG. 2 , the tail cap assembly  30  includes a tail cap  28  and a conductive spring member  32 . The tail cap  28  preferably includes a region of external threads  34  for engaging the matching aft threads  22  formed on the interior of the barrel  12 . Other suitable means may also be employed for attaching the tail cap  28  to the barrel  12 . The tail cap  28  may have a different exterior configuration than that shown in  FIGS. 1-2 . For example, the exterior surface of the tail cap  28  may include knurling. Also, a portion of the material comprising the tail cap  28  may be removed so that a rib is formed with a hole for a lanyard. 
     A sealing element  36  may be provided at the interface between the tail cap  28  and the barrel  12  to provide a watertight seal. The sealing element  36  may be an O-ring or other suitable sealing devices. In the illustrated embodiment, the sealing element  36  is a one-way valve formed by a lip seal that is orientated so as to prevent flow from the outside into the interior of the flashlight  10 , while simultaneously allowing overpressure within the flashlight to escape or vent to the atmosphere. Radial spines may be disposed at the interface  35  between the tail cap  28  and the barrel  12  to ensure that the end of the barrel  12  does not provide a gas tight seal against the adjacent flange of the tail cap  28 , thereby impeding the flow of overpressure gases from the interior of the flashlight. 
     The design and use of one-way valves in flashlights are more fully described in U.S. Pat. No. 5,003,440 issued to Anthony Maglica, which is hereby incorporated by reference. 
     In the present embodiment, barrel  12  and tail cap  28  are formed out of metal, preferably aircraft grade aluminum. Further, the barrel  12 , tail cap  28 , and conductive spring member  32  form part of the ground return path from a negative electrode of the light source  14 . The conductive spring member  32  is electrically coupled to the case electrode of the battery  16  and the tail cap  28 . Tail cap  28  is in turn electrically coupled to the barrel  12  through interface  35 . Thus, when the tail cap assembly  30  is installed in the barrel  12 , the conductive spring member  32  forms an electrical path between the case electrode of the battery  16  and the tail cap  28 , and the tail cap  28  forms an electrical path between the conductive spring member  32  and the barrel  12  through, for example, interface  35  and/or the mating threads  22 ,  34 . 
     To facilitate the flow of electricity, any existing surface treatments, such as by anodizing, disposed at the tail cap/barrel contact and the interface between conductive spring member  32  and tail cap  28  should be removed. 
     In addition to acting as a conductor in the main power circuit, the conductive spring member  32  also urges the batteries  16  toward the front of the flashlight  10 . As a result, the center electrode of the rear battery is in electrical contact with the case electrode of the next forward battery. In this way, the batteries  16  contained in the barrel  12  are electrically coupled. The center electrode of the forward-most battery  16  is urged into contact with a compressible positive contact  54  of lighting module  40 . 
     Referring to  FIG. 3 , the lighting module  40  is disposed at the forward end of the barrel  12  and in the present embodiment, among other things, holds the light source  14  relative to a reflector  106  of the head assembly  20 . The light source  14  includes a first, positive electrode in electrical communication with the positive contact  54  via second circuit board  58  and a second, negative electrode in electrical communication with the heat sink housing  44 . The light source  14  may be any suitable device that generates light. For example, the light source  14  can be an LED lamp, an incandescent lamp, or an arc lamp. In the illustrated embodiment, the light source  14  is an LED lamp and lighting module  40  is an LED module. LED  37  of lighting module  40  preferably substantially radiates light at a spherical angle of less than 180°. In other embodiments, LEDs with other angles of radiation may be used, including LEDs that radiate at an angle greater than 180°. 
     The structure of an LED module that may be used for lighting module  40  is described in detail in co-pending U.S. patent application Ser. No. 12/188,201, which is hereby incorporated by reference. 
     Lighting module  40  together with the retaining collar  42 , barrel  12 , and head assembly  20  form a mechanical power switch corresponding to mechanical power switch  41  shown in the circuit diagram of  FIG. 6 . The contacts of the mechanical power switch  41  comprise the contact  21  of the annular region  24  and the heat sink housing  44  of the lighting module  40 . In  FIG. 3 , the flashlight  10  is shown in the OFF condition (i.e., switch  41  is open). To close switch  41  and turn flashlight  100 N, the head assembly is rotated in the counterclockwise direction relative to the barrel so that the head assembly  20  is axially translated away from the barrel and the heat sink housing  44  comes into contact with contact  21 , thereby closing the circuit of the flashlight  10  and turning the flashlight  10  ON. To turn flashlight  10  OFF, the head assembly is rotated in the opposite, clockwise, direction so that the head assembly is axially translated toward the barrel and pushes the heat sink housing  44  of lighting module  40  out of contact with contact  21  of the barrel  12 . 
       FIG. 4  is a cross-sectional view of the lighting or LED module  40  in isolation. The LED module  40  of the present embodiment includes an LED  37  as light source  14 , a first circuit board  38 , a lower assembly  45  formed by compressible positive contact  54  and a lower insulator  56 , a second circuit board  58 , an upper assembly  70  formed by an upper insulator  72  and an upper positive contact  74  and an upper negative contact (not shown), and a heat sink  80  formed by the outer heat sink housing  44  and a contact ring  81 , which are preferably made out of metal. 
     For redundancy, the compressible positive contact  54  preferably includes two clips  55  for making electrical contact with second circuit board  58 , one of the clips  55  being displaced before the page in the cross-sectional view provided in  FIG. 4 . The second circuit board  58  is in electrical contact with upper positive contact  74  and an upper negative or ground contact, which are preferably solder connected to the bottom side of the first circuit board  38 . For redundancy, the upper positive contact  74  preferably includes two clips  76 , one of which is displaced before the page in the view provided in  FIG. 4 . The upper ground contact also includes two clips  76  for making electrical contact with the second circuit board  58 , one of which is displaced behind the clip  76  of the upper positive contact shown in  FIG. 4  and one of which is displaced before the page in the view provided in  FIG. 4 . The upper positive contact  74  is in electrical communication with the positive electrode of LED  37  via first circuit board  38  and the upper ground contact is in electrical communication with the heat sink  80  via the first circuit board  38 . 
     The LED  37  and the heat sink  80  are affixed to the first circuit board  38 , preferably via a solder connection. The first circuit board  38 , which preferably is a metal clad circuit board having a plurality of thermally conductive layers connected by thermal vias, promotes the rapid and efficient transfer of heat from the LED  37  to the heat sink  80 . 
     The LED  37  can be any light emitting diode that can be soldered to a printed circuit board. Preferably the LED  37  can be soldered to the first circuit board  38  using a screen applied solder paste and a reflow oven. More preferably, the LED  37  is the LUXEON® Rebel product commercially available from Philips Lumileds Lighting Company, LLC. 
     The second circuit board  58  includes the circuitry for operating flashlight  10  and making it function as a multi-mode flashlight. 
     The lower assembly  45  is preferably formed by co-molding compressible positive contact  54  and a lower insulator  56  together. Likewise, upper assembly  70  is preferably formed by co-molding upper insulator  72  and an upper positive contact  74  and an upper negative contact together. Thus, the upper and lower insulator are preferably formed from an injection moldable plastic with suitable structural and thermal qualities for the application. 
     The upper positive and negative contacts of the upper assembly  70  are soldered to the bottom of the first circuit board  38 , the front side of which is in turn soldered to contact ring  81 , which can be press fit and/or soldered to heat sink housing  44 . Thus, the upper assembly  70  is firmly held within heat sink housing  44  in the present embodiment. Further, the circumference of heat sink housing  44  is crimped into an annular recess  83  of the lower insulator  56 . The crimping of heat sink housing  44  into annular recess  83  holds lower insulator  56  and hence the lower assembly  45  within heat sink housing  44 . 
     During manufacture, prior to the lower insulator  56  being coupled to the heat sink housing  44  with the second circuit board  58  positioned therebetween, a potting material may be provided into the lower insulator  56 . Accordingly, the second circuit board  58  may be inserted into the potting material as the lower insulator  56  is coupled to the heat sink housing  44 . This potting material may serve to protect the second circuit board if the flashlight  10  is dropped later when in use. The potting material may comprise an epoxy resin or other suitable material. The lower insulator  56  may be filled halfway with the potting material, but other volumes of potting material may be used. 
     When flashlight  10  is in the ON state, the heat sink housing  44  thermally and electrically couples the light source  14  and the barrel  12 . In addition, the heat sink housing  44  electrically couples the ground path of the second circuit board  58  to the barrel  12 . The heat sink housing  44  therefore acts as the negative, or ground, contact for the lighting module  40 . Further, by arranging the heat sink housing  44  as shown in  FIG. 2  so that it is in good thermal contact with the barrel  12  when the flashlight  10  is ON, heat that is generated by the light source  14  is efficiently absorbed and/or dissipated by the first circuit board  38  to contact ring  81 , the heat sink housing  44  and finally barrel  12 . Thus flashlight  10  is able to effectively protect the light source  14  from being damaged due to heat. Preferably, the heat sink housing  44  is made from a good electrical and thermal conductor, such as aluminum. 
     The heat sink housing  44  is formed so that it flares in a region  78  toward the back or bottom of the LED module  40  from a first region  77  having a first diameter to a second region  79  having a second, larger diameter. The diameter of the first region  77  is sized so that it can fit within the annular lip  24  without coming in contact with the annular lip  24 . The outer diameter of the lower insulator  56  is sized so that there is little or no play in the radial direction between the inner wall of the barrel and the lower insulator  56 . In this way, the heat sink housing  44  can be kept from contacting the barrel  12  except when LED module  40  is pushed far enough forward within barrel  12  so that the flared region  78  of the heat sink housing  44  comes into contact with the contact  21  of the annular lip  24  of barrel  12 . 
     The outer surface of the heat sink housing  44  also includes an annular recess  82  in the region  77  of the first diameter. The annular recess  82  is generally perpendicular to the axis of the heat sink and the barrel  12 . In addition, the annular recess  82  is positioned to receive locking tabs  85  (see  FIG. 5 ) of retaining collar  42  when the LED module  40  is mounted within the barrel  12 . 
     The flared region  78  of the heat sink housing  44  is preferably shaped to mate with contact  21  along as much surface area as possible to facilitate electrical and thermal communication between the LED module  40  and the barrel  12 . The flared region  78  of the heat sink housing  44  is also sized so that once disposed in the barrel  12 , the axial movement of the heat sink housing  44 , and, consequently, the LED module  40 , in the forward direction will be limited by the annular lip  24  of the barrel  12 . 
     The lower insulator  56  includes at its back face  88  a recess  89 , which is surrounded by an annular shoulder  90  so that the recess is centrally located. The recess  89  is dimensioned to be deeper than the height of the center electrode of battery  16 . However, as shown in  FIGS. 2 and 3 , when the forward most battery  16  is urged forward against the back face  88  of the lower insulator  56 , the center electrode of battery  16  engages with the compressible positive contact  54 . In this way, the LED module  40  provides a simple configuration that enhances the electrical coupling between components even when the flashlight is jarred or dropped, which may cause the battery or batteries  16  to suddenly displace axially within the barrel  12 . Further, because the compressible positive contact  54  may absorb impact stresses due to, for example, mishandling and recess  89  is deeper than the center electrode of the forward most battery  16 , the battery&#39;s center electrode and the electronics of the flashlight provided on second circuit board  58  are well protected from physical damage during use of the flashlight  10 . 
     Also, because the compressible positive contact  54  is disposed forward of the shoulder  90  of back face  88 , if a battery or batteries  16  are inserted backwards into the barrel  12  so that their case electrodes are directed forward, no electrical coupling with compressible positive contact  54  is formed. Accordingly, the configuration of the LED module  40  and its arrangement within barrel  12  will help to protect the flashlight&#39;s electronics from being affected or damaged by reverse current flow. In another embodiment, the electronics of flashlight  10  are protected from reverse current flow by the use of a diode included in the electrical circuit of the flashlight. 
     Referring to  FIGS. 2 and 3 , the lighting module  40  is disposed generally in the forward end of the barrel  12 . Absent further assembly, the lighting module  40  is urged forward by the action of the conductive spring member  32  on batteries  16  until the flared region  78  of the heat sink housing  44  comes into contact with the annular lip  24  of the barrel  12 . The retaining collar  42  attaches to the heat sink housing  44  of the lighting module  40  and, among other things, limits axial movement of the lighting module  40  in the rearward direction beyond a predetermined distance. The retaining collar  42  attaches to the lighting module  40  at the annular recess  82  of the heat sink housing  44 . 
     Referring to  FIGS. 3, 5A and 5B , the retaining collar  42  includes circumferential locking tabs  85 , which project inwardly from the inner surface of the retaining collar  42 , and ribs  86 , which project outwardly from the outer surface of the retaining collar  42 . Referring to  FIG. 3 , each of the locking tabs  85  is sized to fit into the annular recess  82  on the exterior of the heat sink housing  44 . A plurality of ribs  86  are preferable spaced equally around the exterior circumference of the retaining collar  42  so as to generally extend in the axial direction of the retaining collar  42 . The ribs  86  preferably extend from the front of the retaining collar to slightly over half the axial length of retaining collar  42 . The ribs  86  are dimensioned so as to limit the amount of radial play between the forward end of the lighting module  40  and the inner diameter of the barrel  12  to a desirable amount. The ribs  86  are also preferably dimensioned to project outwardly from retaining collar  42  by the same or a greater distance than the locking tabs  85  project inwardly. By only having the ribs extend to about the middle of the of the retaining collar  42 , the aft end  87  of the retaining collar  42  can expand sufficiently over the outer surface of the heat sink housing  44  within the barrel  12  until circumferential locking tabs  85  snap into annular recess  82  (see  FIG. 3 ). Once the circumferential locking tabs  85  are snapped into annular recess  82 , the rearward movement of the lighting module  40  is confined by the annular lip  24 . Thus, by securing the retaining collar  42  to the lighting module  40 , which is disposed in the barrel  12 , the retaining collar  42  keeps the lighting module  40  from falling to the rear of barrel  12 , and potentially out the back end of the flashlight  10 , in the absence of batteries  16  being installed in the flashlight  10 . In a preferred embodiment, the retaining collar  42  is made from an insulator such as, for example, plastic. 
     Referring to  FIG. 3 , the head assembly  20  is disposed on the forward end of barrel  12 . The head assembly  20  includes a face cap  102 , a lens  104 , a reflector  106 , and a head  108 . The reflector  106  and the lens  104  are rigidly held in place by the face cap  102 , which is threadably coupled to the head  108 . The head  108  includes threads  112  formed on its inside diameter that engage with the forward threads  18  of the barrel  12 . Arranged this way, the reflector  106  may be displaced in the axial direction of the flashlight  10  by rotating the head assembly  20  relative to the barrel  12 . 
     In a preferred implementation of the illustrated embodiment, the tail cap  28 , the barrel  12 , the face cap  102  and the head  108 , generally forming the external surfaces of the flashlight  10 , are manufactured from aircraft quality, heat treated aluminum, which may be selectively anodized. The non-conductive components are preferably made from polyester plastic or other suitable material for insulation and heat resistance. 
     Referring back to  FIG. 3 , the reflective profile  118  of the reflector  106  is preferably a segment of a computer-generated optimized parabola that is metallized to ensure high precision optics. Optionally, the reflective profile  118  may include an electroformed nickel substrate for heat resistance. 
     Preferably the profile  118  is defined by a parabola having a focal length of less than 0.080 inches, and more preferably between 0.020-0.050 inches. Further, the distance between the vertex of the parabola defining the profile  118  and the aft opening of the reflector  118  is preferably 0.080-0.130 inches, more preferably 0.105-0.115 inches. The opening of the forward end of the reflector  106  preferably has a diameter of 0.7-0.8 inches, more preferably 0.741-0.743 inches, and the opening of the aft end of the reflector  106  preferably has a diameter of 0.2-0.3 inches, more preferably 0.240 to 0.250 inches. Further, the ratio between the distance from the vertex to the opening of the aft end of the reflector  106  and the focal length is preferably in the range of 1.5:1 and 6.5:1, more preferably 3.0:1 to 3.4:1. Moreover, the ratio between the distance from the vertex to the opening of the forward end of the reflector  106  and the focal length is preferably in the range of 20:1 and 40:1, more preferably 26:1 to 31:1. 
     In the illustrated flashlight  10 , the reflector  106  may be selectively moved in the axial direction relative to the light source  14 . By rotating the head assembly  20  relative to the barrel  12  the head assembly  20  travels along the forward threads  18  of the barrel  12  and causes the reflector  106  to axially displace relative to the light source  14 . By varying the axial position of the reflector  106  relative to the light source  14 , the flashlight  10  varies the dispersion of light produced by the light source  14 . In this way, the flashlight  10  can be adjusted between spot and flood lighting. 
     Although the illustrated embodiment employs mating threads to enable the movement of the reflector  106  axially relative to the light source  14 , in other embodiments other mechanisms may be employed to achieve an adjustable focus feature. 
     Further, because the head assembly  20  of the illustrated embodiment does not form part of the electrical circuit, it may be completely removed from the barrel  12  of the flashlight  10  so that the tail cap  28  end of the flashlight  10  may be inserted into the head assembly  20  and the flashlight used in a “candle mode.” 
     Referring back to  FIG. 3 , although the embodiment disclosed herein illustrates a substantially planar lens  104 , the flashlight  10  may instead include a lens that has curved surfaces to further improve the optical performance of the flashlight  10 . For example, the lens may include a biconvex profile or a plano-convex profile in the whole or part of the lens surface. 
     A sealing element, such as an O-ring  75 , may also be incorporated at the interface between the face cap  102  and the lens  104 , the face cap  102  and the head  108 , and the head  108  and the barrel  12  to provide a watertight seal. 
     The electrical circuit of flashlight  10  will now be described. Referring to  FIGS. 2-4 , the electrical circuit of flashlight  10  is shown in the open or OFF position. The electrical circuit is closed, or is in the ON position, when the head assembly  20  is rotated to sufficiently translate the lighting module  40  in the forward direction so that the flared region  78  of the heat sink housing  44  electrically couples with the contact  21  of the barrel  12 . Once the circuit is closed, electrical energy is conducted from the rear battery  16  through its center contact which is in connection with the case electrode of the battery  16  disposed forward thereof. Electrical energy is then conducted from the forward-most battery  16  to the compressible positive contact  54  of the lighting module  40 . The electrical energy is then selectively conducted through the electronics on the second circuit board  58  through the upper positive contact  74  and to the positive electrode of the light source  14  via the first circuit board  38 . After passing through the light source  14 , the electrical energy emerges through the negative electrode of the light source  14  which is electrically coupled to heat sink  80  via the first circuit board  38 . The heat sink housing  44  of heat sink  80  is electrically coupled to the contact  21  of barrel  12 . The barrel  12  is coupled to the tail cap  28 , which is in electrical contact with the conductive spring member  32 . Finally, the conductive spring member  32  of the tail cap assembly  30  completes the circuit by electrically coupling with the case electrode of the rearmost battery. In this manner, a main power circuit is formed to provide electrical energy to illuminate the light source  14 . 
     In the present embodiment, a parallel ground path is also formed from the second circuit board  58  to the heat sink housing  44  through upper ground contacts attached to the upper end of the second circuit board  58  and the first printed circuit board  38 , which is in turn in electrical contact with the heat sink  80 . Thus, the controller provided on the second circuit board  58  may remain powered at all times when the mechanical power switch  41  is closed, even if the electronics on the second circuit board  58  modulate the light source  14  on and off. 
     Referring to  FIG. 3 , to open the electrical circuit of flashlight  10 , the user may twist or rotate the head assembly  20  to translate the lighting module  40  in the aft direction until the flared region  78  of the heat sink housing  44  separates from the contact  21  of the barrel  12 . 
     Although the illustrated embodiment of flashlight  10  is turned ON by causing the head assembly  20  to move away from the barrel and turned OFF by causing the head assembly  20  to axially translate toward the barrel  12 , through a simple reconfiguration of lighting module  40 , the retaining collar  42 , and the annular lip  21 , the flashlight  10  could be made to operate in the inverse order. In other words, so that axial movement of the head assembly  20  away from the barrel  12  would cause the flashlight to turn OFF and axial movement of the head assembly  20  toward the barrel  12  would cause it to turn ON. 
     Further, although a rotating type mechanical power switch that opens and closes the electrical circuit at the barrel/heat sink housing has been described, the electrical circuit may be closed or opened at other locations. Moreover, although a rotating type mechanical power switch has been described, the various aspects of the invention as described herein are not limited by the type of mechanical power switch employed. Other suitable mechanical power switches, including, for example, push-button and sliding type mechanical power switches may also be employed. 
     The multi-mode operation of flashlight  10  will now be described. The flashlight  10  is preferably provided with a plurality of modes of operation. In the embodiment described below, the flashlight  10  is provided with four modes of operation. Each mode of operation allows the flashlight  10  to perform one of four specific features of the flashlight  10 , such as, for example, normal operation, power save, blink, or SOS. When the flashlight  10  is initially turned ON, or if flashlight  10  has been turned OFF for more than a predetermined period of time, the flashlight  10  will automatically operate in a first, default mode of operation. While the flashlight  10  is in the first operating mode, if it is turned OFF for a period of time, which is less than or equal to a predetermined period of time, and then turned back ON, the flashlight  10  will change to a second operating mode. While the flashlight  10  is in the second operating mode, if it is again turned OFF for a period of time, which is less than or equal to a predetermined period of time, and then turned back ON, the flashlight  10  will change to a third operating mode. In the same manner, while the flashlight  10  is in the third operating mode, if it is again turned OFF for another period of time, which is less than or equal to a predetermined period of time, and then turned back ON, the flashlight  10  will change to a fourth operating mode. 
     In the present embodiment, the predetermined period of time is set to be equal to one and a half (1.5) seconds, which is a relatively short period of time, but more than sufficient for an operator of flashlight  10  to manipulate the head assembly  20  to turn OFF flashlight  10  and then turn flashlight  10  back ON. In other embodiments, a shorter or longer period may be desirable. However, the predetermined period is preferably less than 3 seconds, otherwise flashlight  10  will have to sit idle too long for the average user before it can be returned to its default mode of operation without indexing through all of the modes of operation. 
     In the embodiment described above, while the flashlight  10  is in the fourth operating mode, if it is turned OFF for a short period of time and then turned back ON, the flashlight  10  will change back to the first operating mode. Yet in an embodiment with more than four modes of operation, if the flashlight  10  is turned OFF for a period of time that is less than or equal to the predetermined period of time and then turned back ON, the flashlight  10  will change to a fifth operating mode, and so on. Regardless of the number of included modes of operation, e.g., 2 to N, the flashlight  10  preferably cycles back to the first mode of operation after reaching the last mode programmed into the electronics of the flashlight. 
     Preferably, the first operating mode is a normal mode in which the light source  14  of flashlight  10  is provided with maximum power as long as the mechanical power switch  41  remains closed. The second operating mode in the present embodiment is a power saving mode in which the light source  14  of flashlight  10  is operated at reduced power (e.g., 50% power) in order to extend the life of the batteries. The third operating mode of the present embodiment is a blink mode in which the light source  14  is flashed on and off at a predefined frequency or preprogrammed frequency pattern that is perceptible to the human eye. The fourth operating mode is an SOS mode in which the light source  14  is automatically flashed to signal SOS in Morse code. 
       FIG. 6  is one embodiment of a circuit diagram for the flashlight  10  of  FIG. 1 . In the embodiment of  FIG. 6 , the circuit for the flashlight  10  of  FIG. 1  includes batteries  16 , electronic switch  117 , light source  14 , mechanical power switch  41 , controller  140 , and state machine  150 . In the illustrated embodiment, the light source  14  is an LED. In other embodiments, the light source  14  may be incandescent lamp or arc lamp. 
     The mechanical power switch  41  in the present embodiment corresponds to the mechanical power switch formed by lighting module  40 , retaining collar  42 , barrel  12 , and head assembly  20 . As illustrated, the contacts of mechanical power switch  41  in the present embodiment comprise heat sink housing  44  and contact  21  of barrel  12 . 
     The controller  140  is preferably a microcontroller, such as, for example, ATtiny13 which is an 8-bit microcontroller manufactured by Atmel Corporation of San Jose, Calif. In other embodiments, the controller  140  may be a microprocessor, an ASIC, or discrete components. 
     In the present embodiment, the batteries  16  are arranged electrically in series so that there is a positive electrode  122  and a negative electrode  124 , with the positive electrode  122  corresponding to the positive electrode of the front-most battery and the negative electrode  124  corresponding to the negative electrode of the rear-most battery. In other embodiments, the batteries may be arranged electrically in parallel. 
     The electronic switch  117  has a voltage input  126 , a voltage output  128  and a duty cycle input  131 . The light source  14  has a first, positive electrode  58  and a second, negative electrode  59 . The mechanical power switch  41  includes heat sink housing  44  as a first, contact and contact  21  of barrel  12  as a second contact. The controller  140  has a power input  146 , a ground  148 , a plurality of data ports  142 ,  144  and a duty cycle output  130 . The state machine  150  has a plurality of state ports  182 ,  184  and a ground connection  156 . 
     In the present embodiment, the positive electrode  122  of the batteries  16  is electrically coupled to the voltage input  126  of the electronic switch  117  and the power supply input  146  of the controller  140 . The voltage output  128  of the electronic switch  117  is electrically coupled to the first, positive electrode  58  of the light source  14 . The second, negative electrode  59  of the light source  14  is electrically coupled to the first contact (heat sink housing  44  in the present embodiment) of the mechanical power switch  41 . Therefore, when the second contact (contact  21  of barrel  12 ) of mechanical power switch  41  is brought into contact with the first contact, so that the mechanical switch  41  is closed, a first closed circuit loop (corresponding to the main power circuit of flashlight  10 ) is formed in which electric current flows from the batteries  16 , through the electronic switch  117 , the light source  14 , and the mechanical power switch  41 . 
     The electronic switch  117  and the light source  14  are considered the load of the first closed circuit loop. When the switch  41  is open, the load is electrically disconnected from the batteries  16 . 
     In one embodiment, the electronic switch  117  is a power transistor, preferably a p-channel MOSFET, since switching is being performed on the high-side in the circuit of the present embodiment. In an embodiment in which switching is performed on the low-side of the circuit, than an n-channel MOSFET would be desirable. In still another embodiment, electronic switch  117  may be a load switch including a current-limited p-channel MOSFET, such as the FPF 2165 manufactured by Fairchild Semiconductor. A current-limited load switch may provide downstream protection to systems and loads which may encounter large current conditions. For example, it may be desirable to use such a load switch if the flashlight embodiment includes three or more batteries  16  in series. 
     In the present embodiment, the positive electrode  122  of the batteries  16  is also connected to the power input  146  of the controller  140 . The ground  148  of the controller  140  connects to the first contact of the mechanical power switch  41 . Therefore, when mechanical power switch  41  is closed, a second closed circuit loop is also formed in which an electric current flows from the batteries  16 , through the controller  140 , and the mechanical power switch  41 . The controller  140  is considered the load of the second closed circuit loop. When the mechanical power switch  41  is open, the load of the second loop, namely the controller, is electrically disconnected from the batteries  16 . 
     Accordingly, as shown in  FIG. 6 , the main power circuit includes a mechanical power switch  41  and an electronic switch  117  disposed electrically in series with the light source  14 . Further, controller  140  is electrically coupled in series with the mechanical power switch  41  so that when the mechanical power switch  41  is opened, the controller  140  is not powered by the batteries  16 . The controller  140  includes an output  130  for providing a control signal for controlling the opening and closing of the electronic switch  117 . The controller is also configured to control the electronic switch  117  in a manner to provide at least two modes of operation as discussed below. 
     The state machine  150  comprises a memory mechanism for temporarily storing a mode of operation. It includes at least one output (e.g., outputs  182  and  184 ) coupled to the controller  140  for communicating at least one output signal to the controller  140 . As discussed in more detail below, the controller  140  is configured to determine the mode of operation based on the at least one output signal from the state machine  150 . The controller  140  also writes a new mode of operation to the state machine  150  following power up. 
     In the present embodiment, the electronic switch  117 , the controller  140 , and the state machine  150  all reside on second circuit board  58  of the lighting module  40 . In other embodiments, they may reside on separate circuit boards, and may reside in locations other than the lighting module  40 . 
     In the present embodiment, the mechanical power switch  41  is used as the user interface for the multi-mode flashlight  10  in addition to serving as the main power switch. Accordingly, the controller  140  is required to interpret the actuations of the mechanical power switch  41  as inputs from the user and change the operational mode of flashlight  10  accordingly. 
     Because the load  117 ,  14 ,  140 , and in particular the controller  140 , is un-powered every time the switch  41  is in the OFF position, when switch  41  is once again closed to turn the flashlight  100 N, the controller  140  has no intrinsic way of knowing what state or mode the flashlight  10  was in the last time the mechanical power switch  41  was closed. Accordingly, the state machine  150  is used to provide state information of the flashlight  10  to the controller  140  every time flashlight  10  is turned ON by mechanical power switch  41 . 
       FIG. 7  is a circuit diagram showing one embodiment of a state machine  150  for the flashlight  10  of  FIG. 1 . In the embodiment of  FIG. 7 , two RC timing circuits are used. One is shown on the left of state machine  150  and the other is shown on the right of state machine  150 . The left RC circuit includes a capacitor  152  electrically coupled in parallel to a bleed off resistor  162 . A charging resistor  172  is interposed between the parallel RC circuit  152 ,  162  and the state port  182  of the state machine  150 . The resistor  172  is also connected in series with the RC circuit  152 ,  162 . The state port  182  is electrically coupled to the data port  142  of the controller  140 . 
     The configuration of the right RC circuit is similar to the left RC circuit. A capacitor  154  is electrically coupled in parallel to a bleed off resistor  164 . A charging resistor  174  is electrically interposed between the parallel RC circuit  154 ,  164  and the state port  184  and is in series with the RC circuit  154 ,  164 . The state port  184  is further coupled to the data port  144  of the controller  140 . Both RC circuits  152 ,  162  and  154 ,  164  are coupled to ground connection  156 , which is further coupled to the first contact (heat sink housing  44 ) of the mechanical power switch  41 . 
     The capacitance of capacitors  152 ,  154  and the resistors  162 ,  164  are preferably selected so as to provide a time constant of greater than about 3 seconds and less than about 4 seconds. For example, in one embodiment, the capacitance of the capacitors  152 ,  154  is set at 2.2 uF, and the resistance of the bleed off resistors  162 ,  164  is set at 1.5 MΩ. As a result, the nominal time constant (τ) for each parallel RC circuit is equal to 3.3 seconds (2.2 uF×1.5 MΩ). This time constant represents the time for each of the capacitors  152 ,  154  to decay to 37% of their charged voltage value. Thus, if the fully charged voltage on each of the capacitors  152 ,  154  is three (3) volts before the flashlight  10  is turned OFF, the voltage on each of the capacitors  152 ,  154  would be approximately 1.11 volts after the time constant of 3.3 seconds is elapsed. By contrast, the resistance of charging resistors  172 ,  174  is preferably set very low (e.g. 10 kΩ) so that the time constants (τ) of the RC circuits  172 ,  152  and  174 ,  154  is very short (e.g. 22 ms), so that the capacitors  152  and  154  can be fully charged by controller  140  almost instantaneously (e.g., 110 ms in the present embodiment). In general the resistance of charging resistors  172 ,  174  should be set so that capacitors  152 ,  154  are charged in a period of time that is substantially shorter than it would take a user to turn ON and then OFF flashlight  10  during normal operation. In general, the bleed off resistor preferably has a resistance of at least two orders of magnitude greater than the charge resistor. 
     When the mechanical power switch  41  is opened or in the OFF position, the voltage stored on capacitors  152 ,  154  will decay at a given rate that is dependent on the value of the capacitor  152 ,  154  and bleed off resistors  162 ,  164 , respectively. When the mechanical power switch  41  is closed so that the flashlight  10  is turned back ON, there will be a residual voltage remaining across each of capacitors  152 ,  154 . The residual voltage on each capacitor  152 ,  154  is measured by the controller  140  upon power up when the mechanical power switch  41  is closed. The controller  140  interprets the residual voltage remaining on each capacitor  152 ,  154  as an ON or an OFF (i.e., as a 1 or a 0), depending on the voltage it measures for each capacitor. Based on the interpreted state of each capacitor, the controller  140  determines and implements the appropriate mode of operation for flashlight  10 . Table 1 below, summarizes each operational mode the controller  140  of the present embodiment is configured to implement based on the state of each capacitor  152 ,  154  at the time the controller  140  is powered up. In other embodiments, other modes may be included or the modes may be associated with different states of capacitors  152 ,  154 . 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Summary of operating modes and voltage values on capacitors C1 and C2. 
               
            
           
           
               
               
               
            
               
                   
                 Voltage Value Present At 
                 Voltage Value Set After 
               
               
                   
                 Power Turn ON 
                 Power Turn ON 
               
               
                   
                 (current mode) 
                 (next mode) 
               
            
           
           
               
               
               
               
               
            
               
                 Mode 
                 C1 (152) 
                 C2 (154) 
                 C1 (152) 
                 C2 (154) 
               
               
                   
               
               
                 Normal 
                 0 
                 0 
                 0 
                 1 
               
               
                 Power Save 
                 0 
                 1 
                 1 
                 0 
               
               
                 Blink 
                 1 
                 0 
                 1 
                 1 
               
               
                 SOS 
                 1 
                 1 
                 0 
                 0 
               
               
                   
               
            
           
         
       
     
     As can be seen from the foregoing, controller  140  can readily use the residual voltage stored on capacitors  152 ,  154  to determine the operational mode of the flashlight  10  each time the controller  140  is powered up. Further, as shown in Table 1, using two parallel RC circuits ( 152 ,  162  and  154 ,  164 ) allows four modes of operation. More modes can be implemented by using more parallel RC circuits. Because each capacitor can be used to represent two logic values, the number of available operating modes can be 2 n , wherein n is the number of parallel RC circuits. For example, one RC circuit yields a maximum of two operating modes, two RC circuits yields a maximum of four operating modes, and three RC circuits yields a maximum of eight operating modes, etc. 
     Beneficially, if the mechanical power switch  41  is left open or in the OFF position for a sufficient period of time, the residual voltage across capacitors  152 ,  154  will decay to zero (0) volts, regardless of their original state. As a result, when the controller  140  is turned on again, the controller  140  will measure no voltage on either capacitor  152  or  154  and, as shown in Table 1, put the flashlight  10  into the first or “Normal” mode of operation. 
     How controller  140  interprets the residual voltage remaining on each capacitor  152 ,  154  as being in the ON or OFF state (i.e., as a 1 or a 0) is now explained. In one embodiment, the residual voltage remaining on each capacitors  152  and  154  at power up is measured by an analog-to-digital converter (ADC) which is embedded in the controller  140 . The measured voltages are then compared against a voltage stored in non-volatile memory. If the measured voltage is equal to or greater than the voltage stored in memory for the capacitor, then the capacitor is treated as being in the ON state, whereas if the measured voltage for a capacitor is less than the stored voltage for the capacitor, it is treated as being in the OFF state. The voltage stored in memory for each capacitor  152 ,  154  may, for example, correspond to what the residual voltage across each capacitor should be after a predetermined time threshold has lapsed from the opening of mechanical power switch  41 , for example, 1.5 seconds. This means that if the user wants to switch from the normal mode to power save mode, he/she would be able to turn the flashlight  10  off for up to 1.5 seconds before turning it back on, and the flashlight will change to the power save mode. Any longer time would cause the flashlight to return to the normal mode. 
     While the decay voltage value stored in non-volatile memory for each capacitor  152 ,  154  may be calculated based on the decay formula V c =Ee −t/τ , a more preferred approach is to empirically determine the voltage stored on each capacitor  152 ,  154  after the desired predetermined period has lapsed and then store the residual value for that capacitor in non-volatile memory for the future reference of controller  140 . 
     Because the manufacturing tolerances for capacitors is relatively high, the actual capacitance of a capacitor can vary significantly from its nominal value, as well as from the actual capacitance of another capacitor having the same nominal capacitance. As a result, capacitors with the same nominal capacitance can discharge at substantially different rates during bleed off, with higher capacitance capacitors taking longer to drain than lower capacitance capacitors. In order to remove such variability from the system, in a preferred embodiment, a calibration procedure is performed during manufacturing to normalize or calibrate the discharge rate of each capacitor  152 ,  154 . A detailed description of an embodiment of the calibration procedure is described below. 
     Once second circuit board  58  is manufactured, the board is connected to an LED to simulate the load of the flashlight  10  while the relevant pin of the controller is driven low to provide a calibration signal to the controller. The controller and load are then powered and both capacitors  152 ,  154  fully charged. Power to the controller  140  and LED is then cut off for an exact interval, for example, 1.5 seconds. After the set time interval has passed, the circuit is powered up and the voltage value on each capacitors  152 ,  154  is precisely measured by the controller  140 , which then stores the measured voltage values for each capacitor in non-volatile memory, such as an EEPROM embedded in the controller  140 . The voltage value stored in non-volatile memory for each capacitors  152 ,  154  now precisely reflects the decay voltage threshold for each capacitor after the predetermined period (e.g., 1.5 seconds) has lapsed. This procedure thus removes the effects of capacitor tolerance that could affect the on/off timing of the multiple flashlight modes. 
     The predetermined period is preferably greater than or equal to 0.75 second and less than or equal to 3.0 seconds. More preferably, the predetermined period is greater than or equal to 1.0 second and less than or equal to 2.0 seconds. Still more preferably, the predetermined period is 1.5 seconds. 
     The operation of the flashlight  10  between different modes will now be described in connection with Table 1 and  FIG. 7 . When the flashlight  10  is initially turned ON or turned ON after 1.5 seconds has lapsed, the flashlight  10  is operated in a normal mode. The controller  140  then charges capacitor C 2   154  through the charging resistor  174  by pulling up the data port  144 . For example, if the flashlight includes 3 batteries in series, the voltage across capacitor  152  will be approximately 4.5 volts, whereas if the flashlight  10  only includes two batteries then the voltage across capacitor  154  will be approximately 3.0 volts. Simultaneously, the controller  10  discharges capacitor C 1   152  by pulling down the data port  142  and consequently, the voltage across capacitor C 1   152  will be approaching 0 volts. As shown in the two right-most columns of Table 1, the logic value of capacitor C 1   152  is set to 0 and the logic value of capacitor C 2   154  is set to 1. In the illustrated embodiment, the value of charging resistors  172 ,  174  are preferably set at 10 KC) or less so that capacitors  152 ,  154  can be fully charged in about 50 ms or less. 
     While the flashlight  10  is in the Normal mode, if it is turned OFF for less than, for example, 1.5 seconds and then turned back ON, the voltage value measured at data port  142  will be approaching 0 volts and the voltage value measured at data port  144  will be higher than the 1.5 second voltage threshold value stored in the non-volatile memory. The controller  140  compares the voltage values presented at data ports  142 ,  144  to the corresponding values in memory and determines that the correct mode of operation is now the second mode, which is a power save mode. The controller  140  then charges capacitor C 1   152  and discharges capacitor C 2   154  using the method described in the normal mode. As shown in Table 1, the logic value of capacitor C 1   152  is set to 1 and the logic value of capacitor C 2   154  is set to 0. 
     While the flashlight  10  is in the power save mode, if it is turned OFF for less than, for example, 1.5 seconds and then turned back ON, the voltage value measured at data port  144  will be approaching 0 volts and the voltage value measured at data port  142  will be higher than the 1.5 seconds voltage threshold value stored in the non-volatile memory. The controller  140  compares the voltage values presented at data ports  142 ,  144  to the corresponding values in memory and determines that the correct mode of operation is now the third mode, which is a blink mode. The controller  140  then charges both capacitors C 1   152  and C 2   154 . As shown in Table 1, the logic value of capacitors C 1   152  and C 2   154  are both 1. While the flashlight  10  is in the Blink mode, the light source visibly blinks ON and OFF at a frequency stored in the controller  140 . 
     While the flashlight  10  is in the Blink mode, if it is turned OFF for less than, for example, 1.5 seconds and then turned back ON, the voltage value measured at both data ports  142  and  144  will be higher than each of their corresponding 1.5 seconds voltage threshold values stored in the non-volatile memory. The controller  140  compares the voltage values presented at data ports  142 ,  144  to the corresponding values in memory and determines the correct mode of operation is now a fourth mode, which is an SOS mode. The controller  140  then discharges both capacitors C 1   152  and C 2   154 . As shown in Table 1, the logic value of capacitors C 1   152  and C 2   154  are both 0. 
     As reflected by Table 1, the above process may continue indefinitely while the user indexes through the various modes of operation programmed into the controller  140 . 
     In the embodiment illustrated in  FIG. 7 , RC circuits  152 ,  162  and  154 ,  164  are used as the temporary memory means or devices state machine  150  for memorizing the next mode of operation that controller  140  is to implement at power up. In other embodiments, energy storage devices other than capacitors  152  and  154  may be used. For example, inductors may be used in parallel with the bleed off resistors  162 ,  164  instead of capacitors  152 ,  154  to form RL circuits as the temporary energy storage means or devices. In this manner an LC timing circuit would be connected to data ports  142 ,  144 . 
     If flashlight  10  is configured to hold 3 batteries  16  in series, the electronic switch  117  preferably comprises a current-limited load switch to regulate the current provided to light source  14  to a desired level, particularly if light source  14  comprises an LED. Preferably, the electronic switch  117  modulates the DC current from the batteries  16  to a pulsed current. The current limited switch can be a commercial device such as FPF2165 manufactured by Fairchild Semiconductor. The output current delivered to the light source  14  can be set by a resistor connected to the ISET pin of the current-limited switch. However, because current-limited load switches of this type have a higher than desired tolerance (e.g., ±25%), if the output current for the switch is set per design requirements to 500 mA, for example, and the switch has a tolerance of ±25%, the actual range of possible output currents for the load switch would be between 375 mA and 625 mA. The manufacturing tolerance of the current-limited load switch would, therefore, produce undesirable intensity differences from flashlight to flashlight. 
     To minimize light to light fluctuations, the following procedure may be employed to calibrate or normalize the output of the electronic switch  117 . First, the ISET resistor for the current-limited load switch may be selected based on a minimum output current desired to be output from electronic switch  117  and delivered to the light source  14 . Because of the wide manufacturing tolerances of the current-limited devices, almost all of the devices will actually output a current above the desired output current limit unless modulated. Accordingly, the controller  140  is configured to control the port  130 , and hence the duty cycle input  131  of the electronic switch  117 , using a pulse-width modulation (PWM) signal. By adjusting the duty cycle of this PWM signal, the average output current from the electronic switch  117  can be controlled to the desired level. 
     The duty cycle the controller uses to control the average output current of the current-limited electronic switch  117  to the desired level is stored in non-volatile memory, such an EEPROM embedded in the controller. During the calibration procedure, the initial duty cycle value stored in memory is set at 100% and is then decremented during a functional test until the appropriate duty cycle is reached to produce the desired average output current from the electronic switch  117 . In one embodiment, the duty cycle of the current-limited electronic switch  117  is decremented until the electronic switch delivers an output current of 525 mA to the light source  14 . Once the desired average current is achieved, the duty cycle resulting in the desired average current is stored back in the non-volatile memory of the controller  114  so that the light source  14  will always operate at that maximum duty cycle during the different modes of operation, with the exception of the power save mode. In the power save mode, the duty cycle is further decremented to result in the desired power savings from the “Normal” mode (e.g., 25% or 50%). 
     In the foregoing discussion, a current-limited load switch was employed as electronic switch  117  to limit the current delivered to light source  14 . In other embodiments, in which it is desired to increase or decrease the current provided by the batteries  16  or other portable source of power to the light source  14 , as shown in  FIG. 8 , a current regulating circuit  160  may be electrically interposed between the output from electronic switch  117  and the light source  114 . Depending on the design requirements, current regulating circuit  160  may be a conventional boost converter, buck converter, or boost/buck converter. 
       FIG. 9  illustrates a circuit diagram for a regulating circuit  160  comprising a boost converter  162  for boosting the average current delivered to light source  14  from, for example, two batteries  16  connected in series. The boost converter circuit includes a microchip  163 , a switching transistor  164 , an inductor  165  disposed in series with the electronic switch  117  and light source  14 , and a current sense resistor  166  connected in series with the emitter of the switching transistor  164 . Capacitors  167 ,  168  are also provided in the present embodiment between the Vcc pin and the STDN pin and ground for the microchip  163 . This is done to limit the voltage drop on the input supply caused by transient in-rush current when the inductor  165  is charging. In the boost converter circuit  162  shown in  FIG. 9  light source  14  is supplied with a pulsed current to maximize battery life. In other embodiments, the boost converter may be arranged in a conventional manner to provide a constant current to maximize brightness of light source  14 . In one embodiment, microchip  163  preferably comprises a ZXSC310E5 by Zetex Semiconductors. Switching transistor  163  is preferably a bipolar transistor, but may also comprise other switching transistors. Other boost converter circuits may also be employed, including boost circuits that provide a continuous DC current output to the light source  14 . 
       FIG. 10  illustrates an alternative circuit involving a boost circuit to drive the light source  14 , such as an LED. As shown, this circuit includes a regulating circuit  190  that may power the controller  140  as well as the light source  14 . More specifically, the output  128  of the regulating circuit  190  may be connected to the power input  146  of the controller  140 . As such, the controller  140  may be powered by the same voltage as applied to the light source  14 , such as an LED. An advantage of this circuit is that the controller need not be powered by the batteries thereby avoiding the situation where battery voltage dips sufficiently to provide insufficient power to the controller  140 . 
     The controller  140  may be coupled to the regulating circuit  190  as shown. The regulating circuit  190  includes an input EN and is grounded (GND) as shown. The regulating circuit  190  may be similar to that shown in  FIG. 9  though different configurations of the regulating circuit may be used. 
     In the circuit of  FIG. 10 , the controller  140  is configured to control port  130  and thus the signal  131  input EN into the regulating circuit  190 . The controller  140  may control the input signal  131  to the regulating circuit  190  using a PWM signal. As such, the regulating circuit  190  of  FIG. 10  acts as a current regulating circuit to provide energy to the light source  14  through PWM so that the LED or other light source  14  may be “dimmed” by PWM. In other words, the light is turned on and off at an appropriate duty cycle and frequency to control the average brightness that is seen by the user. 
     A problem would arise, however, if during the off cycle of the PWM signal provided to the regulating circuit  190 , power is also not provided to the controller  140  such that the controller  140  would turn off. To address this issue, the circuit of  FIG. 10  provides that the current regulating circuit described above is converted to a voltage regulating circuit during the off phase of the PWM. In this manner, the regulating circuit  190  converts between a current regulating circuit during the on cycle of the PWM signal and a voltage regulating circuit during the off cycle of the PWM signal. 
     During the off cycle of the PWM signal, the voltage may be regulated to 2.0 volts which is preferably enough to operate the microcontroller  140 , but not enough to forward bias the light source  14 , such as an LED. The voltage may be regulated to other levels as desired. Accordingly, during the off cycle of the PWM signal, the controller  140  may still be powered while the LED  14  is off thereby providing the desired dimming of the light source  14  while the controller  140  remains powered. 
     In one example, the output of the regulating circuit  190  may switch between about 3.2 volts to power the light source  14 , and 2.0 volts (so that the controller remains powered) at a 50% duty cycle. In other words, the power to the microcontroller  140  may be considered adequate 100% of the time, while only 50% of the time, the power is adequate to emit light from the LED (i.e., the light would be dimmed by 50%). 
     While various embodiments of an improved flashlight and its respective components have been presented in the foregoing disclosure, numerous modifications, alterations, alternate embodiments, and alternate materials may be contemplated by those skilled in the art and may be utilized in accomplishing the various aspects of the present invention. For example, the circuits described above may be used in flashlight and lighting devices other than the flashlight shown in  FIG. 1 . Thus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention as claimed below.