Patent Publication Number: US-2023142534-A1

Title: Portable lighting device

Description:
RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 16/689,359, filed Nov. 20, 2019, which claims priority benefit to Chinese Utility Model Application No. 201822007596.4, filed Nov. 30, 2018, the entire contents of each of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to lighting devices. More specifically, the present disclosure relates to portable lighting devices having adjustable light outputs. 
     BACKGROUND 
     Portable lighting devices such as torches are commonly used for illumination. These devices typically include a light source selectively powered by a power source. 
     SUMMARY OF THE DISCLOSURE 
     In one embodiment, a portable lighting device comprises a housing defining a central longitudinal axis, a clip coupled to the housing, a light source supported by the housing, and a power source positioned within the housing and coupled to the light source. The housing includes a plurality of longitudinally-extending surfaces arranged at different angles around the central longitudinal axis to direct light from the light source in various directions when resting on a support surface. The clip is rotatable relative to the housing about the central longitudinal axis to serve as a stand when resting on the support surface. 
     In another embodiment, a portable lighting device comprises a housing, a light source supported by the housing, a power source positioned within the housing and coupled to the light source, and a controller positioned within the housing and coupled to the light source and the power source. The controller is operable to execute a ramp-up algorithm and/or a ramp-down algorithm to control an intensity of light outputted by the light source based on a remaining charge in the power source. 
     In one embodiment, a portable lighting device includes a housing, a light source supported by the housing, and a power source positioned within the housing and coupled to the light source. The power source is configured to provide a drive current to the light source, and an intensity of the light source is dependent on the drive current. The portable lighting device may further include an actuator positioned on the housing and an electronic processor positioned within the housing and coupled to the light source, the power source, and the actuator. The electronic processor is configured to determine that the actuator has been actuated, determine a first operation mode of the light source in response to determining that the actuator has been actuated, measure a voltage of the power source, determine whether to operate the light source in the first operation mode by comparing the voltage of the power source to a predetermined threshold associated with the first operation mode, and control the drive current to operate the light source in a second operation mode in response to determining that the voltage of the power source is less than the predetermined threshold, wherein the drive current of the second operation mode is less than the drive current of the first operation mode. The first operation mode may be a high mode and the second operation mode may be a low mode. The first operation mode may be a low mode and the second operation mode may be an off mode. The electronic processor may be configured to control the drive current by controlling a pulse width modulation (PWM) duty cycle that controls when the power source provides the drive current to the light source. The light source may include at least one light emitting diode. 
     In another embodiment, a portable lighting device includes a housing, a light source supported by the housing, and a power source positioned within the housing and coupled to the light source. The power source is configured to provide a drive current to the light source, and an intensity of the light source is dependent on the drive current. The portable lighting device may further include an electronic processor positioned within the housing and coupled to the light source and the power source. The electronic processor may be configured to measure a voltage of the power source, determine that the voltage of the power source is less than a first predetermined threshold, control the drive current to operate the light source in a low current operation mode, determine whether the voltage of the power source is greater than a second predetermined threshold, wherein the second predetermined threshold is lower than the first predetermined threshold, increase the drive current in response to determining that the voltage of the power source is greater than the second predetermined threshold, determine whether the drive current has increased to be greater than or equal to the drive current of a high current operation mode of the light source, and in response to determining that the drive current has increased to be greater than or equal to the drive current of the high current operation mode of the light source, control the drive current to operate the light source in the high current operation mode. The electronic processor may be further configured to in response to determining that the drive current has not increased to be greater than or equal to the drive current of the high current operation mode of the light source, repeat the steps of delaying a predetermined period of time, determining whether the voltage of the power source is greater than the second predetermined threshold, further increasing the drive current in response to determining that the voltage of the power source is greater than the second predetermined threshold, and determining whether the drive current has increased to be greater than or equal to the drive current of the high current operation mode of the light source. The electronic processor may be configured to, in response to determining that the voltage of the power source is less than the second predetermined threshold, control the drive current to operate the light source in the low current operation mode without increasing the drive current. The portable lighting device may include an actuator positioned on the housing and coupled to the electronic processor, wherein the electronic processor may be configured to determine a selected operation mode of the light source in response to determining that the actuator has been actuated. The electronic processor may be configured to control the drive current by controlling a pulse width modulation (PWM) duty cycle that controls when the power source provides the drive current to the light source. The power source may include at least one alkaline battery. 
     In another embodiment, a portable lighting device includes a housing, a light source supported by the housing, and a power source positioned within the housing and coupled to the light source. The power source may be configured to provide a drive current to the light source, and an intensity of the light source is dependent on the drive current. The portable lighting device may include an electronic processor positioned within the housing and coupled to the light source and the power source. The electronic processor may be configured to measure a voltage of the power source, determine a drive current threshold based on the voltage of the power source, control the drive current to be a first value, determine whether the drive current is greater than the drive current threshold, and in response to determining that the drive current is less than the drive current threshold, repeating the steps of increasing the drive current, delaying a predetermined time period, and determining whether the increased value of the drive current is greater than the drive current threshold. The electronic processor may be further configured to, in response to determining that the increased value of the drive current is greater than the drive current threshold, cease increasing of the drive current and control the drive current to be the increased value to operate the light source. The first value of the drive current may correspond to one of a low current operation mode of the light source and an off mode of the light source. The electronic processor may be configured to control the drive current by controlling a pulse width modulation (PWM) duty cycle that controls when the power source provides the drive current to the light source. 
     In another embodiment, a portable lighting device includes a housing, a light source supported by the housing, and a power source positioned within the housing and coupled to the light source, wherein the power source is configured to provide a drive current to the light source, and an intensity of the light source is dependent on the drive current. The portable lighting device may further include an electronic processor positioned within the housing and coupled to the light source and the power source. The electronic processor may be configured to control the drive current to operate the light source in a selected operation mode, monitor a voltage of the power source, determine whether the voltage of the power source is less than a power-off threshold, in response to determining that the voltage of the power source is greater than the power-off threshold, repeating the steps of decreasing the drive current, delaying a predetermined time period, and determining whether the voltage of the power source is less than the power-off threshold. The electronic processor may be further configured to, in response to determining that the voltage of the power source is less than the power-off threshold, control the drive current to cease providing the drive current to the light source to turn off the light source. The electronic processor may be further configured to decrease the drive current by reducing a pulse width modulation (PWM) duty cycle that controls when the power source provides the drive current to the light source. Repeating the steps of decreasing the drive current, delaying the predetermined time period, and determining whether the voltage of the power source is less than the power-off threshold may include ramping down the drive current over a plurality of time stages, wherein the electronic processor is configured to decrease the drive current such that the drive current reaches a respective predetermined value at an end of each time stage. During a final stage of the plurality of time stages, the electronic processor may be configured to control the drive current to be maintained at a constant value until the voltage of the power source is less than the power-off threshold. During a final stage of the plurality of time stages, the electronic processor may be configured to monitor the drive current provided by the power source to the light source, control a drive current pulse width modulation (PWM) duty cycle to be maintained at a constant value until the monitored drive current is less than a low drive current threshold, and, in response to determining that the monitored drive current is less than a low drive current threshold, control the drive current to cease providing the drive current to the light source to turn off the light source. The portable lighting device may further include an actuator positioned on the housing and coupled to the electronic processor. The electronic processor may be configured to control the drive current to operate the light source in the selected operation mode by controlling the drive current to operate the light source in a low current operation mode, delaying a predetermined period of time, determining the selected operation mode of the light source based on the actuator being actuated, measuring the voltage of the power source, determining a starting value of the drive current based on the selected operation mode of the light source and the voltage of the power source, and controlling the drive current to be the starting value. The selected operation mode may be a high current operation mode and the electronic processor may be configured to control the drive current to ramp up to the high current operation mode by measuring the voltage of the power source, determining that the voltage of the power source is less than a first predetermined threshold, controlling the drive current to operate the light source in a low current operation mode, determining whether the voltage of the power source is greater than a second predetermined threshold, wherein the second predetermined threshold is lower than the first predetermined threshold, increasing the drive current in response to determining that the voltage of the power source is greater than the second predetermined threshold, determining whether the drive current has increased to be greater than or equal to the drive current of the high current operation mode of the light source, and, in response to determining that the drive current has increased to be greater than or equal to the drive current of the high operation current mode of the light source, control the drive current to operate the light source in the high current operation mode. The electronic processor may be configured to, in response to determining that the drive current has not increased to be greater than or equal to the drive current of the high current operation mode of the light source, repeat the steps of delaying a predetermined period of time, determining whether the voltage of the power source is greater than the second predetermined threshold, further increasing the drive current in response to determining that the voltage of the power source is greater than the second predetermined threshold, and determining whether the drive current has increased to be greater than or equal to the drive current of the high current operation mode of the light source. 
     In another embodiment, a portable lighting device includes a housing, a light source supported by the housing, and an alkaline battery positioned within the housing and coupled to the light source, wherein the alkaline battery is configured to provide a drive current to the light source, and an intensity of the light source is dependent on the drive current. The portable lighting device may also include an electronic processor positioned within the housing and coupled to the light source and the alkaline battery. The electronic processor may be configured to monitor a voltage of the alkaline battery, and execute a ramp-up algorithm to control the drive current based on the voltage of the alkaline battery. 
     In another embodiment, a portable lighting device includes a housing, a light source supported by the housing, and an alkaline battery positioned within the housing and coupled to the light source, wherein the alkaline battery is configured to provide a drive current to the light source, and an intensity of the light source is dependent on the drive current. The portable lighting device may also include an electronic processor positioned within the housing and coupled to the light source and the alkaline battery. The electronic processor may be configured to monitor a time that the light source has been operating, and execute a ramp-down algorithm to control the drive current based on the time that the light source has been operating. 
     Other aspects of the disclosure will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of a portable lighting device including a light source. 
         FIG.  2    is an end perspective view of the lighting device with a battery cap removed. 
         FIG.  3    is a perspective view of the lighting device positioned on a support surface in a first configuration. 
         FIG.  4    is a perspective view of the lighting device positioned on the support surface in a second configuration. 
         FIG.  5    is a cross-sectional view of the lighting device taken along section line  5 - 5  of  FIG.  1   . 
         FIG.  6    is a perspective view the lighting device with a lens of the light source removed. 
         FIGS.  7 A- 7 B  illustrate configurations of the lighting device magnetically attached to a magnetic surface. 
         FIG.  8    is an exploded view of the lighting device, illustrating magnetic elements. 
         FIG.  9    is another exploded view of the lighting device. 
         FIG.  10    is a flowchart illustrating a method of operating the lighting device. 
         FIG.  11    is a flowchart illustrating a method of operating a ramp-up algorithm for the lighting device according to one embodiment. 
         FIG.  12    is a flowchart illustrating a method of operating a ramp-down algorithm for the lighting device according to one embodiment. 
         FIG.  13    is a flowchart illustrating another method of operating a ramp-down algorithm for the lighting device. 
         FIG.  14    is a flowchart illustrating another method of operating a ramp-down algorithm after setting an initial drive current based on a selected operation mode for the lighting device. 
         FIG.  15    is a graph of the LED current during execution of the ramp-down algorithm of  FIG.  14    when the lighting device is operating in the HIGH mode. 
         FIG.  16    is a graph of the LED current during execution of the ramp-down algorithm of  FIG.  14    when the lighting device is operating in the LOW mode. 
         FIG.  17    is a block diagram of the lighting device according to one example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the disclosure are explained in detail, it is to be understood that the application is not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The application is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     Use of “including” and “comprising” and variations thereof as used herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Use of “consisting of” and variations thereof as used herein is meant to encompass only the items listed thereafter and equivalents thereof. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly to encompass both direct and indirect mountings, connections, supports, and couplings. 
     As described herein, terms such as “front,” “rear,” “side,” “top,” “bottom,” “above,” “below,” “upwardly,” “downwardly,” “inward,” and “outward” are intended to facilitate the description of the lighting device of the application, and are not intended to limit the structure of the application to any particular position or orientation. 
       FIG.  1    illustrates a portable lighting device  100 , such as a personal floodlight or flashlight, including a housing  105 , a light source  110 , a power button  115 , and a clip  120 . The housing  105  has a generally elongated cuboidal shape and with a rectangular or square cross-section. The housing  105  defines a central longitudinal axis A extending through opposing ends of the housing  105 . In other embodiments, the housing  105  may be configured as other geometric shapes. The housing  105  supports and encloses the other components of the lighting device  100 . 
     Referring to  FIG.  2   , the housing  105  includes a battery cap  125  at one end of the lighting device  100 . The battery cap  125  is selectively removable from the remainder of the housing  105  via a locking mechanism  130 . In the illustrated embodiment, the locking mechanism  130  is a bayonet-style locking mechanism, allowing the battery cap  125  to removably couple to the housing  105  via a clockwise or counterclockwise twisting motion (e.g., in the direction of arrow  135 ). When coupled to the remainder of the housing  105 , the battery cap  125  encloses a power source  145  (e.g., a battery or battery pack) for powering the lighting device  100 . The battery cap  125  further includes a biasing element  140 . In the illustrated embodiment, the biasing element  140  is a coil spring, although other types of biasing elements may also or additionally be used. When the battery cap  125  is coupled to the housing  105  via the locking mechanism  130 , the biasing element  140  compresses and applies a force along the longitudinal axis A on the power source  145 . The force helps maintain the power source  145  in proper electrical connection with electrical contacts within the housing  105  to operate the light source  110 . 
     Referring to  FIG.  3   , the housing  105  also includes a plurality of longitudinally-extending surfaces  105 A,  105 B,  105 C,  105 D arranged around the longitudinal axis A. The surfaces  105 A- 105 D extend generally parallel to the longitudinal axis A and meet at corner areas  150  to form the generally elongated cuboid shape of the housing  105 . In the illustrated embodiment, the corner areas  150  are configured as slanted edges disposed on the housing  105  along each of the four longitudinal edges parallel to the longitudinal axis A. The surfaces  105 A- 105 D are oriented at different angles relative to each other to support the lighting device  100  at different orientations. For example, the lighting device  100  may be positioned on a support surface (e.g., a table) with a different one of the surfaces  105 A- 105 D resting on the support surface to direct light from the light source  110  in various directions. Although the illustrated housing  105  includes four longitudinal-extending surfaces  105 A- 105 D arranged at different angles, in other embodiments the housing  105  may include fewer or more longitudinally-extending surfaces. 
       FIG.  5    illustrates various internal lighting components comprising the lighting device  100 . The housing  105  encases a carrier  160 , which receives the power source  145 . The housing  105  is held together around the carrier  160  by threaded fasteners  180  (e.g., screws). In other embodiments, other suitable fastening means, such as a snap-fit housing assembly and/or adhesives, may be used to assemble the housing  105 . 
     As shown in  FIGS.  5 ,  6 , and  9   , the light source  110  is supported by the housing  105  and configured to emit light in an outward direction that is normal to the longitudinal axis A. In other embodiments, the light source  100  may emit light along the direction of the longitudinal axis A or in various other directions relative the housing  105 . The light source  110  includes a lens  165  and a plurality of light emitting elements  170 . In the present embodiment, the lens  165  is a clear, injection molded plastic piece with a light refraction index that enhances the transmission of light emitted by the light emitting elements  170 . In other embodiments, other materials may be used as the lens  165  to achieve different refraction indexes and different transmission factors. 
     The illustrated light emitting elements  170  are light emitting diodes (LEDs). In the illustrated embodiment, the light source  110  includes five LEDs  170  (shown in  FIG.  6   ) disposed on a printed circuit board (PCB)  175 . In other embodiments, the light source  110  may include fewer or more light emitting elements, and/or may include different types of light emitting element (e.g., florescent bulbs, incandescent bulbs, etc.). For example, in some embodiments, the lighting device  100  may be a personal flashlight that only includes one LED. In the present embodiment, the LEDs  170  are driven in synchronism with a relatively constant current or voltage. In other embodiments, the LEDs  170  may be driven separately and with a variable current or voltage. 
     The PCB  175  is powered by the power source  145  and supplies a variable drive current from the power source  145  to the LEDs  170 . In some embodiments, the PCB  175  includes a controller or processor configured to generate a pulse width modulated (PWM) signal that drives the LEDs  170 . The controller is operable to vary the PWM duty cycle to adjust the intensities of the LEDs  170  depending on the operation mode (e.g., HIGH mode, LOW mode, etc.) selected by the user via the power button  115 . In other embodiments, the PCB or other suitable circuitry may generate different types of signals or drive currents to power the LEDs  170  in different modes. Furthermore, the controller is operable to implement a light optimizing control algorithm that monitors a remaining voltage in the power source  145 , which is then used in a control loop to achieve a lumen output that can be supported by the current discharge state of the power source  145 . Details of the controller and control algorithm will be described in further detail in the following description. 
       FIG.  9    shows a reflector  235  disposed between the lens  165  and the PCB  175 . The reflector converges or diverges the light emitted by the LEDs  175  such that the lighting device  100  may achieve a desired intensity and output beam angle. The properties of the reflector  235  may be altered in various embodiments to achieve different light output characteristics. 
     Referring to  FIGS.  1  and  9   , the power button  115  is supported by the housing  105  and disposed above a switch  240 . The switch  240  is electrically coupled between the power source  145  and the light source  110  (more particularly, the PCB  175  of the light source  110 ). When the power button  115  is depressed, the power button  115  actuates the switch  240  to select an operation mode of the lighting device  100 . The selected operation mode is then electrically transmitted and temporarily stored in the PCB  175 . Based on the stored operation mode, the PCB  175  executes a control algorithm to drive the LEDs  175  with a drive current from the power source  145 . When the power button  115  is depressed, the lighting device  100  cycles between an OFF mode, a HIGH mode, a LOW mode, and back to the OFF mode. If the power button  115  is continuously depressed for an extended period of time exceeding a predetermined time, the lighting device will exit to the OFF mode regardless of the current mode or the next mode in the operation cycle. 
     As shown in  FIGS.  3  and  4   , the clip  120  is rotatably coupled to the housing  105 . The clip  120  is operable to clip to various objects (e.g., a belt, etc.) to provide added portability and convenience to the lighting device  100 . The clip  120  is rotatable about the longitudinal axis A to provide added stability and structural support as a kickstand for the lighting device  100  when the housing  105  rests on one of the longitudinally-extending surfaces  105 A- 105 D (see  FIG.  3   ). The clip  120  also has a substantially flat section  155  that serves as a stand or a resting surface when the clip  120  (instead of one of the longitudinally-extending surfaces  105 A- 105 D) is rotated with respect to the housing  105  to rest on the support surface (see  FIG.  4   ). In this position, the clip  120  supports the entire weight of the lighting device  100  independent of the longitudinally-extending surfaces  105 A- 105 D, allowing the lighting device  100  to rotate while being supported by the clip  120  and to emit light from the light source  110  at different angles determined by the position of the clip  120  relative to the housing  105  as specified by a user. 
     As shown in  FIGS.  7 A,  7 B, and  8   , the lighting device  100  further includes two magnetic elements  185 A,  185 B. The first magnetic element  185 A is a side magnet disposed on a side of the housing  105  opposite from the light source  110 . The second magnetic element  185 B is a cap magnet disposed in the battery cap  125 . The magnetic elements  185 A,  185 B are capable of magnetizing and attracting to magnetic surfaces  190 . The magnetic faces  185 , thereby, allow the lighting device  100  to be conveniently mounted to magnetic surfaces  190  in various orientations. In some embodiments, the first magnetic element  185 A, the second magnetic element  185 B, or both may be omitted. 
       FIG.  8    is an exploded view of the magnetic elements  185 A,  185 B of the lighting device  100 . The first magnetic element  185 A includes a side magnet cover  205 , a first magnet  210 , and a side magnetizer  215 . The side magnetizer  215  is a permanent magnet that arranges the magnetic domains in the first magnet  210  such that the magnetic field in the first magnet  210  increases. The side magnet cover  205  is configured to cover and hold the first magnet  210  and the side magnetizer  215  within the housing  105  of the lighting device  100 . Likewise, the second magnetic element  185 B includes a cap magnet cover  220 , a second magnet  225 , and a cap magnetizer  230 . The cap magnetizer  230  is a permanent magnet that arranges the magnetic domains in the second magnet  225  such that the magnetic field in the second magnet  225  increases. The cap magnet cover  220  is configured to cover and hold the second magnet  225  and the cap magnetizer  230  within the battery cap  125  of the lighting device  100 . The covers  205 ,  220  may be made of a relatively softer material than the magnets  210 ,  225 , such as plastic or elastomeric material, so that the covers  205 ,  220  do not mar the surfaces to which the magnetic elements  185 A,  185 B are attached. 
       FIG.  17    is a block diagram of the lighting device  100  according to one example embodiment. As shown in  FIG.  17   , the lighting device  100  includes an electronic processor  1705 , a memory  1710 , the power source  145 , the light source  110 , and the switch  240 . The electronic processor  1705  is electrically coupled to a variety of components of the lighting device  100  and includes electrical and electronic components that provide power, operational control, and protection to the components of the lighting device  100 . In some embodiments, the electronic processor  1705  includes, among other things, a processing unit  230  (e.g., a microprocessor, a microcontroller, or another suitable programmable device), a memory, input units, and output units. The processing unit of the electronic processor  1705  may include, among other things, a control unit, an arithmetic logic unit (“ALU”), and a plurality of registers  244 . In some embodiments, the electronic processor  1705  is implemented partially or entirely on a semiconductor (e.g., a field-programmable gate array [“FPGA”] semiconductor) chip, such as a chip developed through a register transfer level (“RTL”) design process. 
     In some embodiments, the memory  1710  includes, for example, a program storage area and a data storage area. The program storage area and the data storage area can include combinations of different types of memory, such as read-only memory (“ROM”), random access memory (“RAM”) (e.g., dynamic RAM [“DRAM”], synchronous DRAM [“SDRAM”], etc.), electrically erasable programmable read-only memory (“EEPROM”), flash memory, a hard disk, an SD card, or other suitable magnetic, optical, physical, or electronic memory devices. The electronic processor  1705  is electrically coupled to the memory  1710  and executes instructions that are capable of being stored in a RAM of the memory  1710  (e.g., during execution), a ROM of the memory  1710  (e.g., on a generally permanent basis), or another non-transitory computer readable medium such as another memory or a disc. The electronic processor  1705  is configured to retrieve from memory and execute, among other things, instructions related to the control processes, algorithms, and methods described herein. The electronic processor  1705  is also configured to store information on the memory  1710  such as current thresholds and voltage thresholds corresponding to various modes of the lighting device  100 . 
     In some embodiments, the power source  145  is coupled to and transmits power to the electronic processor  1705  and to the light source  110 . In some embodiments, the power source  145  includes combinations of active and passive components (e.g., voltage step-down controllers, voltage converters, rectifiers, filters, etc.) to regulate or control the power provided to the electronic processor  1705  and/or the light source  110 . In some embodiments, the power source  145  is configured to provide a drive current to the light source  110  based on control signals received from the electronic processor  1705  to control an intensity of the light source  110 . In other words, an intensity of the light source  110  is dependent on the drive current (i.e., power) received from the power source  145 . For example, the electronic processor  1705  is configured to detect a user actuation of the power button  115  by detecting a change in the state of the switch  240 . Based on the detected user actuation, the electronic processor  1705  determines an operational mode for the light source  110  (for example, a high current operation mode, a low current operation mode, an off mode, or the like). The electronic processor  1705  then controls the power source  145  to provide a drive current to the light source that corresponds to the selected operational mode. In some embodiments, the electronic processor  1705  is configured to control the drive current provided by the power source  145  to the light source  110  by controlling a pulse width modulation (PWM) duty cycle that controls when the power source  145  provides the drive current to the light source  110 . 
     In some embodiments, one or more of the components shown in  FIG.  17    may be located on the PCB  175 . In some embodiments, one or more of the components shown in  FIG.  17    may be located elsewhere within or on the housing  105  of the lighting device  100 . In some embodiments, the lighting device  100  includes additional, fewer, or different components than the components shown in  FIG.  17   . For example, the lighting device  100  may additionally include a display to indicate an operational mode of the lighting device  100 . As another example, the lighting device  100  may include current and/or voltage sensors that measure the current being drawn by the light source  330  (i.e., drive current) and/or the voltage of the power source  315 . 
       FIG.  10    is a flowchart illustrating a method  300  of operating the lighting device  100  that is executed by the electronic processor  1705  according to one example embodiment. When the electronic processor  1705  determines that the power button  115  has been depressed by detecting a change in state of the switch  240  (block  300 ), the electronic processor  1705  measures a charge remaining in the power source  145  (i.e., a voltage of the power source  145 ) (block  310 ). The measured remaining charge is then compared to a predetermined threshold (block  315 ) to determine whether the lighting device  100  is capable of being operated in the operation mode selected by the power button  115  (block  320 ). For example, the remaining charge of the power source  145  may indicate whether the power source  145  is able to provide a required amount of drive current to operate the light source  110  in the selected operation mode. If the selected operation mode of the lighting device  100  requires a drive current with a corresponding power source voltage that exceeds the predetermined threshold, the electronic processor  1705  switches to the next mode that requires a lower drive current in the operation cycle. For example, the electronic processor  1705  switches from the HIGH mode to the LOW mode or from the LOW mode to the OFF mode when the charge remaining in the power source  145  (i.e., the voltage of the power source  145 ) is insufficient to support the drive current of the selected HIGH mode or the selected LOW mode. In other words, the electronic processor  1705  controls the drive current to operate the light source  110  in a lower current operation mode that is different than the selected operation mode (at block  320 ) in response to determining (at block  315 ) that the voltage of the power source  145  is less than the predetermined threshold. On the other hand, when the voltage of the power source  145  is determined to be greater than or equal to the predetermined threshold corresponding to a drive current of the selected operation mode (at block  315 ), the electronic processor  1705  controls the drive current to operate the light source  110  in the selected operation mode (at block  320 ). 
     In some embodiments, the power source  145  comprises one or more alkaline batteries (see  FIG.  9   ) received by the carrier  160 . When the batteries become partially depleted, the alkaline chemistry changes and increases the internal impedance of the power source  145 . Therefore, the lighting device  100  experiences a large voltage drop when attempting to draw full power from a partially depleted power source  145 . Although the power source  145  may still have, for example, 50% charge remaining, the large voltage drop resulting from the increased internal impedance may cause the lighting device  100  to prematurely enter the LOW mode due to the charge remaining in the power source  145  decreasing below the predetermined threshold (see block  315  of  FIG.  10   ), which undesirably decreases the intensity of the light outputted by the light source  110  and shortens the operation time in the HIGH mode. 
     In some embodiments, instead of attempting to initially draw full power from a partially depleted power source  145 , the electronic processor  1705  executes a ramp-up algorithm  400 , as shown in  FIG.  11   , to incrementally ramp-up the drive current delivered to the LEDs  170  when the power source  145  is partially depleted. With such an arrangement, the light outputted by the light source  110  is more efficiently controlled based on the remaining charge of the power source  145 . Such control may extend the life of the of the power source  145  and may improve the performance of the lighting device  100  by avoiding undesirable decreases in the intensity of the light outputted by the light source  110 . 
     Referring to  FIG.  11   , when the electronic processor  1705  determines that the power button  115  has been depressed by detecting a change in state of the switch  240  (block  405 ), the electronic processor  1705  executes the ramp-up algorithm  400  and measures the amount of charge remaining in the power source  145  (block  410 ) before generating a PWM signal to provide a substantially constant drive current/voltage to the LEDs  170 . If the measured remaining charge in the power source  145  is above a first voltage threshold (e.g., 2.5 V) signifying more than 50% remaining charge in the power source  145  (decision  415 ), the LEDs  170  are driven with a high drive current (e.g., 820 mA) to operate the lighting device  100  in the HIGH mode (block  420 ). The ramp-up algorithm  400  repeats blocks  410 - 420  to maintain operation in the HIGH mode until the measured remaining charge in the power source  145  is no longer above the first voltage threshold. When the remaining charge in the power source  145  falls below the first voltage threshold or is initially determined to be below the first voltage threshold (at block  415 ), the power source  145  is considered partially depleted. In response to this determination by the electronic processor  1705  (block  415 ), the electronic processor  1705  controls the drive current provided by the power source  145  to the LEDs  170  to be a low drive current (e.g., 165 mA) to operate at a “plateau” state (block  425 ). 
     In the “plateau” state, the remaining charge in the power source  145  is measured again (block  430 ). If the measured remaining charge in the power source  145  is not above a second threshold (e.g., 2.3 V) that is lower than the first voltage threshold (decision  435 ), then the power source  145  is depleted too far to reasonably provide the high drive current necessary for the lighting device  100  to operate in the HIGH mode. Thus, the ramp-up algorithm  400  repeats blocks  425 - 430  to maintain operation in the “plateau” state. On the other hand, if the measured remaining charge in the power source  145  is above the second voltage threshold (decision  435 ), then the drive current is increased (block  440 ), and the electronic processor  1705  controls the power source  145  to drive the LEDs  170  with the increased drive current (at block  443 ). The electronic processor  1705  then determines whether the increased drive current is less than the high drive current corresponding to the HIGH mode (at block  445 ). When the drive current is below the high drive current (at block  445 ), the electronic processor  1705  repeats blocks  425  through  445  until the drive current has increased to be equivalent to or greater than the high drive current (decision  445 ) at which point the lighting device  100  is operating in the HIGH mode (block  420 ). In other words, the electronic processor  1705  incrementally increases the drive current provided to the light source  110  from the low drive current of the LOW mode to the high drive current of the HIGH mode when the power source  145  is determined to be partially depleted. By incrementally increasing the drive current for a partially depleted power source  145 , the ramp-up algorithm  400  works in conjunction with the mode selection operation of the power button  115  to avoid the large voltage drop mentioned above and inhibit the lighting device  100  from prematurely dropping from the HIGH mode to the LOW mode. 
     In another embodiment, the lighting device  100  executes a ramp-up algorithm  500  as shown in  FIG.  12   . When the electronic processor  1705  determines that the power button  115  has been depressed by detecting a change in state of the switch  240  (block  505 ), the electronic processor  1705  controls the drive current provided by the power source  145  to the LEDs  170  to be a low drive current regardless of the remaining charge available in the power source  145  such that the lighting device  100  is operated in the LOW mode (block  510 ). The electronic processor  1705  subsequently measures the remaining charge in the power source  145  (block  515 ). Based on the measured remaining charge, the electronic processor  1705  determines a maximum light output that the lighting device  100  can reasonably achieve and determines a drive current threshold based on the selected light output (block  520 ). In other words, the electronic processor  1705  determines a drive current threshold based on the measured voltage of the power source  145  (at block  520 ). For example, the electronic processor  1705  may access a look-up table in the memory  1710  that includes corresponding drive current thresholds for a plurality of voltages or voltage ranges of the power source  145 . In some embodiments, the look-up table includes corresponding drive current thresholds for a plurality of maximum light output values of the light source  110 . As another example, the electronic processor  1705  may be programmed to use the measured voltage of the power source  145  as a variable in a stored formula that is used to calculate the drive current threshold. 
     Continuing the explanation of the method  500 , as long as the present drive current provided to drive the LEDs  170  does not exceed the drive current threshold (decision  525 ), the ramp-up algorithm  500  increases the present drive current (block  530 ) and drives the LEDs  170  with the increased drive current (block  535 ) so that the intensity of the light emitted by the lighting device  100  is increased. Decision  525  and blocks  530 - 535  are repeated until the present drive current provided to drive the LEDs  170  exceeds the drive current threshold (at block  525 ), signifying that the selected maximum light output is achieved. At this point, the ramp-up algorithm  500  ceases increasing of the drive current and drives the LEDs  170  with the present drive current to maintain the determined maximum light output (block  540 ). By executing the method  500 , the electronic processor  1705  incrementally increases the drive current provided to the light source  110  from a low drive current of the LOW mode to a higher drive current that can be reasonably provided by the power source  145  based on its measured remaining charge. Such control may avoid the large voltage drop mentioned above and inhibit the lighting device  100  from prematurely dropping from the HIGH mode to the LOW mode due to the power source  145  being partially depleted. 
     In alternate embodiments of the ramp-up algorithm  500 , block  510  of  FIG.  12    may be excluded. For example, after the power button  115  is initially pressed (block  505 ), a remaining charge in the power source  145  is measured (block  515 ) and used to select a maximum light output and determine a drive current threshold (block  520 ) before a drive current is provided to drive the LEDs  170 . In such embodiments, the lighting device  100  allows ramping up of the emitted light intensity from the OFF mode as opposed to the LOW mode. 
     It should be understood that in some embodiments, the ramp-up algorithms  400 ,  500  may incrementally increase the drive current in a predetermined number of steps (e.g., ten steps) such that execution of each step increases the drive current by a predetermined amperage (e.g., 100 mA). In other embodiments, the ramp-up algorithm  400 ,  500  may execute a continuous function increase such that the drive current is continuously increased over time with zero or infinite number of steps. Other methods of increasing the drive current in the ramp-up algorithm  400 ,  500  are possible to achieve the same purpose and are not exhaustively detailed herein. Additionally, although not shown in separate blocks in  FIGS.  12  and  13   , in some embodiments, the electronic processor  1705  delays a predetermined time period (e.g., ten milliseconds, fifty milliseconds, five hundred milliseconds, etc.) between driving the LEDs  170  with the increased drive current (blocks  443  and  535 ) and comparing the drive current to a threshold value (blocks  445  and  525 ). 
     The lighting device  100  may also implement a ramp-down algorithm according to some embodiments. The ramp-down algorithm may be implemented by the electronic processor  1705  to slowly decrease the drive current and the corresponding lumen output of the light source  110  according to a function of time, a function of the remaining charge in the power source  145 , or a function of both time and remaining charge. After a steady drive current is set, for example in accordance with one of the ramp-up algorithms  400 ,  500  explained above, and the lighting device  100  operates in accordance with the steady drive current for a predetermined period of time, the lighting device  100  may execute the ramp-down algorithm until reaching a power-off voltage threshold. In some embodiments, the power-off voltage threshold for the lighting device  100  is 2.8 V. 
       FIG.  13    is a flowchart illustrating one embodiment of a ramp-down algorithm  600  implemented by the electronic processor  1705  to decrease the drive current provided by the power source  145  to the light source  110  as a function of time. After the lighting device  100  achieves either the operation mode selected by the power button  115  or the highest possible lumen output from execution of the ramp-up algorithms  400  or  500 , the electronic processor  1705  implements the ramp-down algorithm  600  (block  605 ). The electronic processor  1705  initially maintains the drive current for a relatively short predetermined time period (e.g., forty-five seconds) (block  610 ), during which the duty cycle of the PWM signal provided to the LEDs  170  is held at a constant high percentage in accordance with a ramped up drive current determined by a previously-executed algorithm  400  or  500  (e.g., 100% if the HIGH mode is selected and achieved). After the initial time period has lapsed, the electronic processor  1705  decreases the drive current by reducing the percentage of the PWM duty cycle provided to the LEDs  170  (block  615 ). The electronic processor  1705  controls the power source  145  to drive the LEDs  170  with the decreased drive current (block  620 ). The electronic processor  1705  measures the remaining charge in the power source  145  (block  625 ) and compares the remaining charge in the power source  145  to a power-off threshold (decision  630 ). If the measured remaining charge falls below the power-off threshold (e.g., 2.8 V), the power source  145  has been depleted beyond a reasonable operating range and, in response, the electronic processor  1705  controls the power source  145  to cease providing drive current to the light source  110  which will accordingly cease outputting light (i.e., operate in the OFF mode) (block  635 ). Otherwise, the electronic processor  1705  repeats blocks  615 - 625  and decision  630  until the measured remaining charge in the power source  145  falls below the power-off threshold, and, in response, turns the lighting device  100  off (block  635 ). 
     By repeating blocks  615 - 630 , the electronic processor  1705  decreases the drive current provided to the light source  110  over a relatively long time interval (e.g., five minutes, sixty minutes, etc.) such that the light output by the light source  110  gradually decreases in intensity. Although not shown in  FIG.  13   , in some embodiments, the electronic processor  1705  delays a predetermined time period (e.g., thirty seconds, one minute, five minutes, etc.) between driving the LEDs  170  with the decreased drive current (block  620 ) and comparing the decreased drive current to the power-off threshold (block  630 ). In some embodiments, the electronic processor  1705  ramps down the drive current provided to the light source  110  (by repeating blocks  615 - 630 ) over a plurality of time stages as explained the below example with five time stages. For example, the electronic processor  1705  is configured to decrease the drive current such that the drive current reaches a respective predetermined value at the end of each time stage. Continuing this example, the electronic processor  1705  may determine a present drive current at the beginning of a time stage and may determine a desired decreased drive current for the end of the time stage. The electronic processor  1705  may then determine the number of times that the drive current is to be decreased and an amount by which to decrease the drive current each time to reach the desired decreased drive current by the end of each time stage. 
     In an example implementation of the ramp-down algorithm  600 , the ramp-down process is divided into five time stages. In the first time stage, the electronic processor  1705  maintains the drive current provided to drive the LEDs  170  at 100% PWM duty cycle for a time period of ninety seconds (block  610 ). In other words, the electronic processor  1705  controls the drive current to operate the light source  110  in the HIGH mode for ninety seconds. In the second time stage, the drive current is reduced to 47.0% PWM duty cycle over a time interval of 3.7 minutes (block  615 ) and the LEDs  170  are driven by the drive current (block  620 ). For example, the electronic processor  1705  may incrementally decrease the PWM duty cycle by approximately 11% every thirty seconds until the PWM duty cycle is 47%. Upon the PWM duty cycle reaching 47%, the electronic processor  1705  maintains the PWM duty cycle at 47% until the end of the time stage (i.e., until 3.7 minutes has passed). As another example, the electronic processor  1705  reduces the PWM duty cycle from 100% to 47% at the beginning of the time stage and maintains the PWM duty cycle at 47% for the duration of the second time stage such that the LEDs  170  are driven at 47.0% PWM drive current over the 3.7 minutes. During this time interval, the electronic processor  1705  measures a remaining charge in the power source  145  (block  625 ) and compares the measured remaining charge to a power-off threshold of 2.8 V (decision  630 ). If the measured remaining charge in the power source  145  falls below 2.8 V at any time within the 3.7 minutes, the electronic processor  1705  controls the power source  145  to cease providing drive current to the light source  110  which will put the lighting device  100  in the OFF mode (block  635 ). Otherwise, the lighting device  100  enters the third stage, wherein a ramp-down process similar to that described above for the second time stage is repeated for the third time stage. In the third time stage, the drive current is further reduced to 20.6% PWM duty cycle over a time interval of twenty minutes (block  615 ) such that the LEDs  170  are driven at 20.6% PWM drive current by the end of the third stage or over the duration of the third time stage (block  620 ). The remaining charge in the power source  145  is measured (block  625 ) and compared to the power-off threshold of 2.8 V (decision  630 ) to determine whether the lighting device  100  should enter the OFF mode (block  635 ). If the remaining charge in the power source  145  is still above the power-off threshold at the end of the third time stage (decision  630 ), the lighting device  100  enters the fourth time stage. In stage four, electronic processor  1705  reduces the PWM duty cycle over a time interval of 4.8 minutes (block  615 ) until the LEDs  170  are driven with a drive current of 125 mA by the end of the fourth time stage or over the duration of the fourth time stage (block  620 ). As long as the measured remaining charge in the power source  145  (block  625 ) does not fall below the power-off threshold (decision  630 ), the electronic processor  1705  will continue to execute the ramp-down algorithm  600  by entering the fifth time stage and remain powered on. In the fifth time stage, the electronic processor  1705  controls the PWM duty cycle to maintain the drive current at 125 mA (block  620 ) until the measured remaining charge reaches the power-off threshold (decision  630 ), thereby turning off the lighting device  100  in response (block  635 ). It should be understood that the number of time stages, the PWM percentages and current values, the time values, and the power-off threshold value detailed in the above example of the ramp-down algorithm  600  are examples and may vary in other embodiments. 
       FIG.  14    illustrates another ramp-down algorithm  700  where the electronic processor  1705  determines an initial drive current to be delivered to the LEDs  170  based on the operation mode selected by the power button  115  before ramping down the drive current based on a function of time and monitored drive current provided to the LEDs  170 . After determining the operation mode of the lighting device  100  from user input of the power button  115  by detecting a change in state of the switch  240  (block  705 ), the electronic processor  1705  controls the drive current to operate the light source  110  in a low current operation mode (e.g., a drive current of 100 mA) (block  710 ). After a short delay (e.g., fifty milliseconds), the electronic processor  1705  measures the remaining charge in the power source  145  (block  715 ). Based on the measured remaining charge and the selected operation mode of the lighting device  100 , the electronic processor  1705  determines an initial drive current to deliver to the LEDs  170  (block  720 ). 
     For example, when the HIGH mode is selected by the power button  115 , if the measured remaining charge in the power source  145  is greater than 2.9 V, the electronic processor  1705  controls the drive current to be 820 mA (e.g., by controlling a PWM signal that controls when the power source  145  provides power to the light source  110  as described above). If the measured remaining charge in the power source  145  is between 2.8 V and 2.9 V, the electronic processor  1705  controls the drive current to be 500 mA. If the measured remaining charge in the power source  145  is between 2.7 V and 2.8 V, the electronic processor  1705  controls the drive current to be 400 mA. If the measured remaining charge in the power source  145  is between 2.5 V and 2.7 V, the electronic processor  1705  controls the drive current to be 300 mA. If the measured remaining charge in the power source  145  is lower than 2.5 V, the electronic processor  1705  controls the drive current to be 250 mA until the power source  145  drops below the power-off voltage (e.g., 1.75 V), at which point the electronic processor  1705  controls the lighting device  100  to turn off. 
     On the other hand, when the LOW mode is selected by the power button  115 , if the measured remaining charge in the power source  145  is greater than 2.3 V, the electronic processor  1705  controls the drive current to be 300 mA. Otherwise, if the measured remaining charge in the power source  145  is lower than 2.3 V, the electronic processor  1705  controls the drive current to be 180 mA until the power source  145  drops below the power-off voltage (e.g., 1.75 V), at which point the electronic processor  1705  controls the lighting device  100  to turn off. 
     Once the initial drive current is determined and set by the electronic processor  1705  (block  720 ), the electronic processor  1705  ramps down the drive current (block  725 ), for example, as a function of time and monitored drive current delivered to the LEDs  170 . In some embodiments, the electronic processor  1705  ramps down the drive current in a similar manner as described above with respect to  FIG.  13   . For example, the electronic processor  1705  may ramp down the drive current throughout a process of four time stages when the initial drive current corresponds to either of the HIGH mode or the LOW mode. However, unlike turning off the lighting device  100  based on a monitored voltage of the power source  145  as explained above (block  630  of  FIG.  13   ), during the final time stage of the algorithm  700 , the electronic processor  1705  may maintain the PWM duty cycle that controls the drive current at a constant value until the monitored drive current decreases below a low drive current threshold (e.g., 130 mA). In some situations, such a decrease in drive current may occur despite the PWM duty cycle being maintained at a constant value due to partial depletion of the power source  145 .  FIGS.  15  and  16    illustrate examples of the electronic processor  1705  ramping down the drive current in accordance with the above explanation of block  725  of  FIG.  14   . 
       FIG.  15    shows a graph of the LED current (i.e., drive current) during execution of the ramp-down algorithm  700  when the lighting device  100  is operating in the HIGH mode. In the first time stage  805 , the electronic processor  1705  maintains the drive current provided to drive the LEDs  170  at 820 mA for a time period of forty-five seconds. In other words, the electronic processor  1705  controls the drive current to operate the light source  110  in the HIGH mode for forty-five seconds. In the second time stage  810 , the electronic processor  1705  reduces the drive current provided to the LEDs  170  from 820 mA to 410 mA over a time interval of approximately 5 minutes. In the third time stage  815 , the electronic processor  1705  reduces the drive current provided to the LEDs  170  from 410 mA to 273 mA over a time interval of approximately 16-17 minutes. In the fourth time stage  820 , the electronic processor  1705  reduces the drive current provided to the LEDs  170  from 273 mA to 205 mA over a time interval of approximately 16-17 minutes. After execution of the fourth time stage  820 , the electronic processor  1705  repeatedly calculates and monitors the drive current delivered to the LEDs  170 . If the electronic processor  1705  determines a point  825  at which the drive current delivered to the LEDs  170  falls below a low drive current threshold (e.g., 130 mA), the electronic processor  1705  controls the power source  145  to cease providing a drive current to the light source  110  to turn off the light source  110 . 
       FIG.  16    is similar to  FIG.  15    but shows a graph of the LED current during execution of the ramp-down algorithm  800  when the lighting device  100  is operating in the LOW mode rather than in the HIGH mode. In the first time stage  830 , the electronic processor  1705  maintains the drive current provided to drive the LEDs  170  at 300 mA for a time period of forty-five seconds. In other words, the electronic processor  1705  controls the drive current to operate the light source  110  in the LOW mode for forty-five seconds. In the second time stage  835 , the electronic processor  1705  reduces the drive current provided to the LEDs  170  from 300 mA to 150 mA over a time interval of approximately 63 minutes. In the third time stage  840 , the electronic processor  1705  reduces the drive current provided to the LEDs  170  from 150 mA to 100 mA over a time interval of approximately 63 minutes. In the fourth time stage  845 , the electronic processor  1705  reduces the drive current provided to the LEDs  170  from 100 mA to 75 mA over a time interval of approximately 97 minutes. After execution of the fourth time stage  845 , the electronic processor  1705  repeatedly calculates and monitors the drive current delivered to the LEDs  170 . If the electronic processor  1705  determines a point  850  at which the drive current delivered to the LEDs  170  falls below a low drive current threshold (e.g., 50 mA), the electronic processor  1705  controls the power source  145  to cease providing a drive current to the light source  110  to turn off the light source  110 . 
     In the examples of  FIGS.  15  and  16   , the electronic processor  1705  may reduce the drive current in each time stage in the same manner or in a similar manner as described above with respect to the time stages of  FIG.  13   . Also similar to the explanation of  FIG.  13    above, it should be understood that the number of time stages, the PWM percentages and current values, the time values, and the low drive current threshold values detailed in the above examples of the ramp-down algorithm  700  are examples and may vary in other embodiments. 
     In the present embodiments, the drive current is calculated for the specific states according to a formula including both the drive current of the previous state and the time lapsed during the present state. It should be understood by those skilled in the art that other formulas, calculations, or ramp-down intervals may be implemented in other embodiments not exhaustively disclosed herein. 
     In an alternate embodiment, the electronic processor  1705  may drive the LEDs  170  with an incrementally decreasing drive current until a specified “plateau” threshold is reached, after which the drive current is held constant. Once the drive current reaches the specified “plateau” threshold and is no longer decreased, the remaining charge in the power source  145  is continuously measured and compared to a low voltage threshold (e.g., 10% of maximum charge). If the measured remaining charge falls below the low voltage threshold, the electronic processor  1705  decreases the specified “plateau” threshold and begins decreasing the drive current again until the new “plateau” threshold is reached. Subsequently, the drive current is held constant at that new “plateau” threshold. The remaining charge in the power source is again repeatedly measured and compared to a predetermined power-off threshold (e.g., 2.8 V). If the measured remaining charge falls below the power-off threshold, the lighting device  100  will turn to the OFF mode. The power-off threshold may vary in different embodiments depending on factors such as the characteristics of the power source  145  used by the lighting device  100 . 
     It should be understood that similar to the ramp-up algorithm  400 ,  500  detailed above, the ramp-down algorithms  600  and/or  700  may also incrementally decrease the drive current in a predetermined number of steps or as a continuous function with zero or infinite number of steps. Other methods of implementing the ramp-down algorithm  600  based on factors other than time and/or remaining charge are possible to achieve the same purpose and are not exhaustively detailed herein. 
     In some embodiments, other types of batteries, such as lithium ion batteries, may be used as the power source  145 . In such embodiments, similar ramp-up algorithms may still be employed, even though the lithium-ion chemistries may not experience as large of voltage drops as alkaline chemistries. Furthermore, it should be understood that other additional voltage thresholds may be used in the ramp-up algorithm  400  described above to further control operations of the lighting device  100 . The lighting device  100  may also include additional components in other embodiments not exhaustively detailed herein to achieve the same purpose, and thus would not deviate from the teachings of the present application.