Patent Publication Number: US-11035556-B2

Title: Portable lighting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Application No. 62/663,736, filed Apr. 27, 2018, the entire contents of which are incorporated by reference herein. 
    
    
     FIELD 
     The present invention relates to lighting devices. More specifically, the present invention relates to portable lighting devices that are operable to provide personal lighting to a user. 
     SUMMARY 
     In one embodiment, the invention provides a portable lighting device including a housing defining a longitudinal axis, a light source supported by the housing, and a power source positioned within the housing and coupled to the light source. The portable lighting device also includes a clip rotatably coupled to the housing, and a magnetic element coupled to the housing. 
     In another embodiment, the invention provides a portable lighting device including a housing defining a longitudinal axis, a first support mechanism coupled to the housing, a second support mechanism coupled to the housing, and a light source supported by the housing. The light source is configured to be supported in a plurality of orientations by the first and the second support mechanisms. The portable lighting device also includes a power source positioned within the housing and coupled to the light source. 
     In yet another embodiment, the invention provides a portable lighting device including a housing defining a longitudinal axis, a light source supported by the housing, and a power source positioned within the housing and coupled to the light source. The portable lighting device also includes a clip rotatably coupled to the housing, a first magnetic element coupled to the housing, and a second magnetic element coupled to the housing. 
     In still another embodiment, the invention provides a portable lighting device including 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 to optimize an intensity of light outputted by the light source in relation to a remaining charge in the power source. 
     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. 7A-7B  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. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention 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 actuator (e.g., button)  115 , and a clip  120 . The housing  105  has a generally elongated cuboidal shape 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 ). In other or additional embodiments, the locking mechanism may be any suitable locking mechanism. 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 longitudinally-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 coupling section  152  that couples to the housing  105 , and a substantially flat section  155  that extends from the coupling section and 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 ). With respect to  FIG. 9 , the coupling section  152  includes an aperture  154  through which a portion of the housing  105  extends such that the coupling section  152  is positioned adjacent the locking mechanism  130 . Moreover, the clip  120  is configured to rotate between a first position in which the clip  120  (e.g., the substantially flat section  155 ) is positioned adjacent a first of the longitudinally-extending surfaces  105 A- 105 D of the housing  105 , a second position in which the clip (e.g., the substantially flat section  155 ) is positioned adjacent a second of the longitudinally-extending surfaces  105 A- 105 D ( FIG. 3 ), and an intermediate position in which the clip  120  (e.g., the substantially flat section  155 ) is positioned adjacent the first and second positions ( FIGS. 1 and 2 ). In the first and second positions, the clip  120  (e.g., the coupling section  152 ) abuts stop surfaces  158  on opposite sides of the battery cap  125 , which provide extra support for the clip  120 . In the illustrated embodiment, the clip  120  has a plurality of intermediate positions. For example, the clip  120  has a first intermediate position in which the substantially flat section  155  is positioned adjacent a third of the longitudinally-extending surfaces  105 A- 105 D of the housing  105 , a second intermediate position in which the substantially flat section  155  is positioned in between two longitudinally-extending surfaces  105 A- 105 D, and a third intermediate position in which the substantially flat section  155  is positioned between two other longitudinally-extending surfaces  105 A- 105 D ( FIG. 4 ). In use, 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. 7A, 78, 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 A  185 B, 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. 10  is a flowchart illustrating a method  300  of operating the lighting device  100 . When the power button  115  is depressed (block  300 ), the PCB  175  first measures a charge remaining in 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 ). If the PCB  175  attempts to operate the lighting device  100  in a mode requiring a drive current that exceeds the available charge in the power source  145 , the lighting device  100  will automatically switch to the next mode that requires a lower drive current in the operation cycle. For example, the lighting device  100  will automatically switch from the HIGH mode to the LOW mode and from the LOW mode to the OFF mode when charge remaining in the power source  145  is insufficient to support the required HIGH mode and LOW mode drive currents, respectively. 
     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 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, which undesirably decreases the intensity of the light outputted by the light source  110  and shortens the operation time in the HIGH mode. 
     In the illustrated embodiment, instead of attempting to initially draw full power from a partially depleted power source  145 , the PCB  175  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 optimized in relation to the remaining charge on the power source  145 . 
     Referring to  FIG. 11 , when the power button  115  is initially pressed (block  405 ), the PCB  175  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 in 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, the power source  145  is considered partially depleted and the LEDs  170  are driven with 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, 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 low drive current is incrementally increased (block  440 ) until the low current becomes equivalent to or greater than the high current (decision  445 ) and the lighting device  100  is operating in the HIGH mode (block  420 ). 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 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 power button  115  is initially pressed (block  505 ), the PCB  175  provides a low drive current to the LEDs  170  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 remaining charge in the power source  145  is subsequently measured (block  515 ). Based on a function of the measured remaining charge, the PCB  175  selects a maximum light output that the lighting device  100  can reasonably achieve (block  520 ) and determines a current threshold based on the selected light output (block  525 ). As long as the present drive current provided to drive the LEDs  170  does not exceed the determined current threshold (decision  530 ), the ramp-up algorithm  500  incrementally increases the present drive current (block  535 ) and drives the LEDs  170  with the incremented present drive current (block  540 ) so that the intensity of the light emitted by the lighting device  100  is increased. Decision  530  and blocks  535 - 540  are repeated until the present drive current provided to drive the LEDs  170  exceeds the determined current threshold, signifying that the selected maximum light output is achieved. At this point, the ramp-up algorithm  500  drives the LEDs  170  with the present drive current to maintain the selected maximum light output (block  545 ). 
     Alternatively, other embodiments of the ramp-up algorithm  500  may exclude block  510  of  FIG. 12 . 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 (block  520 ) and determine a current threshold (block  525 ) 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 algorithm  400 ,  500  may incrementally increase the drive current in a predetermined number of steps (e.g., 10 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. 
     The lighting device  100  may also implement a ramp-down algorithm according to some embodiments. The ramp-down algorithm may be implemented in the lighting device  100  to slowly decrease the drive current and the corresponding lumen output 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. 
       FIG. 13  is a flowchart illustrating one embodiment of a ramp-down algorithm  600  implemented according to 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 algorithm  400 ,  500 , the PCB  175  implements the ramp-down algorithm  600  (block  605 ). The drive current is initially maintained over a relatively short time period (block  610 ), during which the duty cycle of the PWM signal provided to the LEDs  170  is held at a constant high percentage (e.g., 100% if the HIGH mode is selected and achieved). After the initial time period has lapsed, the drive current is incrementally decreased over a relatively long time interval by reducing the percentage of the PWM duty cycle provided to the LEDs  170  (block  615 ). The decreased drive current drives the LEDs  170  over the time interval to provide a corresponding lumen output that is decreasing in intensity (block  620 ). During this time interval, the remaining charge in the power source  145  is measured (block  625 ) and compared 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 the lighting device  100  will turn to the OFF mode (block  635 ). Otherwise, blocks  615 - 625  and decision  630  are repeated until the measured remaining charge in the power source  145  falls below the power-off threshold, thereby turning the lighting device  100  OFF (block  635 ). With each iteration of block  615 , the length of the time interval may increase or decrease in various embodiments, as described in the example below. 
     In an exemplary implementation of the ramp-down algorithm  600 , the ramp-down process is divided into five stages. In the first stage, the PCB  175  maintains the drive current provided to drive the LEDs  170  at 100% PWM duty cycle for a time period of 90 seconds (block  610 ). This ensures that the lighting device  100  is consistently operated in the HIGH mode for the initial 90 seconds. In the second stage, the drive current is reduced to 47.0% PWM duty cycle over a time interval of 3.7 minutes (block  615 ) such that the LEDs  170  are driven at 47.0% PWM drive current over the 3.7 minutes (block  620 ). During this time interval, the PCB  175  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 lighting device  100  will turn to the OFF mode (block  635 ). Otherwise, the lighting device  100  enters the third stage, wherein the ramp-down process is repeated. In the third stage, the drive current is further reduced to 20.6% PWM duty cycle over a time interval of 20 minutes (block  615 ) such that the LEDs  170  are driven at 20.6% PWM drive current over the 20 minutes (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 ). In stage four, the duty cycle of the PWM drive current is reduced over a time interval of 4.8 minutes (block  615 ) until the LEDs  170  are driven with 125 mA over the time interval of 4.8 minutes (block  620 ). As long as the measured remaining charge in the power source  145  (block  625 ) does not fall below 2.8 V (decision  630 ), the lighting device  100  will continue to execute the ramp-down algorithm  600  and remain powered on. In stage five, the PCB  175  maintains the drive current at 125 mA (block  620 ) until the measured remaining charge reaches 2.8 V (decision  630 ), thereby turning off the lighting device  100  (block  635 ). It should be understood that the number of stages, the PWM percentages, and the power-off threshold values detailed in this exemplary implementation of the ramp-down algorithm  600  may vary in other embodiments not exhaustively detailed herein. 
     Alternatively, other embodiments of the ramp-down algorithm  600  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%). If the measured remaining charge falls below the low voltage threshold, the ramp-down algorithm  600  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 continuously 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 algorithm  600  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. 
     One or more independent features and/or independent advantages of the portable lighting device may be set forth in the claims.