WO2010027460A2

WO2010027460A2 - Battery powered lighting appliance having substantially constant light output

Info

Publication number: WO2010027460A2
Application number: PCT/US2009/004954
Authority: WO
Inventors: Frank F. Huang
Original assignee: Eveready Battery Company, Inc.
Priority date: 2008-09-02
Filing date: 2009-09-02
Publication date: 2010-03-11
Also published as: WO2010027460A3

Abstract

A lighting appliance includes a contact (102) that receives power, a power regulator (112) that selectively regulates the received power and supplies regulated power to the light source based according to feedback that includes battery characteristics and light source characteristics.

Description

BATTERY POWERED LIGHTING APPLIANCE HAVING SUBSTANTIALLY

CONSTANT LIGHT OUTPUT

TECHNICAL FIELD The following relates generally to a battery powered lighting appliance.

BACKGROUND Conventionally, battery powered lighting appliances such as a portable hand held flashlight, a headlight that affixes to a helmet or a strap wearable around the head of a human, a lantern, a pendent light, a floor light, a table light, etc. use one or more batteries in connection with a current limiting resister and light source. Unfortunately, as the one or more batteries discharge and the voltage drops, the light output intensity or lumen output drops. Consequently, the lumen output dims with appliance usage, and the user of the appliance may be left with an undesirable lumen level. Attempts have been made to mitigate the light output drop by considering the discharge curve of batteries and utilizing PWM. However, theses attempts still fail to yield substantially constant lumen output.

SUMMARY Aspects of the present application address these matters, and others.

In one aspect, a lighting appliance includes a contact (102) that receives operating power, a power regulator (112) that selectively regulates the received power based on the lumen output of the device and outputs power which is less then 100% of the received power, and a light source (108) that is supplied with the regulated power. In another aspect, a lighting appliance includes a contact that receives battery power, a light source 108, and a power regulator 112. The power regulator 112 receives the battery power and supplies regulated power to the light source according to feedback. The feedback includes light source characteristics.

In yet another aspect, a lighting appliance includes a contact that receives battery power, a light source 109, a differential amplifier 816, a sense resistor 920, and a power regulator 112. The power regulator 112 receives the battery power and supplies regulated power to the light source according to feedback. The feedback is a signal from the differential amplifier, created by comparing a voltage across the sense resistor and a reference voltage. The sense resistor is connected in series with the light source 108. In another aspect, a method is disclosed. The method regulates power to a light source 702. Characteristics of the light source are measured or otherwise obtained 704. The regulator power to the light source is adjusted 706 according to the characteristics.

In yet another aspect, a method is disclosed. The method regulates power to a light source 702. An initial regulated power is selected. Characteristics of the light source are measured or otherwise obtained 704. The regulator power to the light source is adjusted

706 according to the characteristics. Optionally, the initial regulated power can be selected by considering one or more use factors, for example, constant output use time, selected lumen output, remaining capacity, and battery chemistry. hi another aspect, a method is disclosed. The method regulates power to a light source 702. Characteristics of the light source are measured or otherwise obtained 704 including measuring a thermal temperature of the light source. The regulator power to the light source is adjusted 706 according to the characteristics. hi yet another aspect, a method is disclosed. The method regulates power to a light source 702. Characteristics of the light source are measured or otherwise obtained 704.

The characteristics include at least one of LED temperature change and droop effect. The regulator power to the light source is adjusted 706 according to the characteristics. In another aspect, a method is disclosed. The method regulates power to a light source 702. Characteristics of the light source are measured or otherwise obtained 704.

The regulator power to the light source is adjusted 706 according to the characteristics. the adjustment is performed by adjusting a voltage output according to a temperature of the light source and current drawn by the light source. Those skilled in the art will recognize still other aspects of the present application upon reading and understanding the attached description. BRIEF DESCRIPTION OF THE DRAWINGS

The present application is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which: Figure 1 illustrates s a block diagram of a lighting appliance.

Figures 2-6 illustrate example embodiment for detecting power source drain. Figure 7 illustrates a method.

Figure 8 illustrates a block diagram of a lighting appliance. Figure 9 illustrates a circuit diagram of a lighting appliance. Figures 10, 11, and 12 are graphs illustrating operation of an example lighting appliance.

Figures 13 and 14 are graphs illustrating discharge curves

DETAILED DESCRIPTION Figure 1 illustrates a block diagram of a lighting appliance 100. The lighting appliance 100 includes a source power electrical contact 102 that receives power from a power source 104 such as one or more batteries external or internal to the lighting appliance 100. The one or more batteries may be a set (one or more) of primary (non- rechargeable) batteries, a set of secondary (rechargeable) batteries, or one or more battery packs, where the batteries in a particular configuration have the same or different physical dimensions and/or electrical properties such as voltage. The illustrated power source 104, in this example, is internal to the lighting appliance 100. In this instance, the appliance 100 includes a battery receiving region configured to alternately receive the set of rechargeable batteries, the set of non-rechargeable batteries, or the one or more battery packs.

The lighting appliance 100 also includes a light source electrical contact 106 configured to receive a light source 108. The light source 108 provides light, measurable in lumens, in response to received power. Generally, the higher the received power, the greater the light output. The light source 108 has a light source voltage, for example, a voltage across an LED, and a light source current, for example the current flowing through the light source. It is appreciated that the light source voltage and/or current can be measured and/or calculated based on other measurements. A suitable light source 108 includes, but is not limited to, an incandescence (e.g., carbon, halogen, etc.), electroluminescence (e.g., LED, solid state, etc.), gas discharge (e.g., fluorescent, neon, plasma, etc.), high intensity discharge (e.g., metal halide, mercury vapor, sulfur, etc.), and/or other based light source. In one instance, the light source 108 is a single light source, while in another instance the light source 108 includes two or more of the same or different types of light sources. It is also to be appreciated that the light sources of the light source 108 may be different colors (e.g., white, red, green, yellow, etc,) and/or rated for different power levels. The light source 108 can include one or more of the above and combinations thereof. A power regulator 112 is located in an electrical path between the source power contact 102 and the light source contact 106. The power regulator 112 controls the power supplied to the light source contact 106, thereby controlling the power supplied to the light source 108. The power regulator 112 may include various circuitry for regulating power. For example, in one instance the power regulator 112 uses pulse width modulation (PWM), pulse frequency modulation (PFM), a combination of PWM and PFM, and/or another approach including PWM and/or PFM or not. In another example, the power regulator 112 controls the power supplied to the light source by adjusting current and/or voltage supplied to the light source 108.

The power regulator 112 controls the regulated power supplied to the light source 108 according to feedback. The feedback can be obtained continuously and/or periodic time periods. The feedback includes information and/or characteristics including, but not limited to, battery chemistry, internal resistance, battery voltage under load, open circuit battery voltage, temperature, measured light output, discharge curve, remaining capacity, estimated light output, current through the light source 108, voltage across the light source 108, changes in the previous characteristics, and the like.

As described in greater detail below, the power regulator 112 can regulate the output power supplied to the light source 108 and thereby facilitate maintaining a substantially constant lumen output of the lighting appliance 100 and/or a substantially constant power output to the light source 108. This may include changing the power supplied to the light source 108 as the power source 104 drains. As such, the lumen output of the light source 108 can be kept substantially constant, for example, for the usable life of the power source 104, unlike other configurations. An optical element 110 converges, diverges or passes the light emitted by the one or more light sources 108. In one instance, the optical element 110 diffuses the light so as to produce directed light, or a light beam. In another instance, the optical element 110 spreads the light so as to produce non-directed light, or a flood light. In yet another instance, the appliance may include more than one optical elements 110, including at least two directed-light optical elements, at least two non-directed-light optical elements, or at least one directed-light and at least one non-directed-light optical element. In another embodiment, the optical element 110 can be omitted.

An interface 114 provides a control for operating the light source 108, including turning one or more of the one or more light sources on and off, adjusting the light intensity of the one or more of the one or more light sources, causing one or more of the one or more light sources to blink, flash, etc., and/or otherwise control the light source 108. The interface 114 may include one or more of a rotary switch, a push button switch, a slide switch, a voice activated switch, etc. Such switches may include two or more positions, with position representing a different mode of operation.

An optional wireless interface (not shown) can be used for remote operation of the appliance 100. The wireless interface may include a receiver configured to receive a wireless signal from a remote device and/or a transmitter configured to transmit information, such as state information, to the remote device. The wireless interface alternatively may be a transceiver with both receiving and transmitting capabilities.

It is to be appreciated that the signal may effectuate operation of the appliance 100. For instance, a received remote signal may invoke one or more of the one or more of the one or more light sources 108 to turn on, turn off, blink, vary the intensity (e.g., via pulse width modulation, etc.), and/or otherwise operate. In another instance, reception of a signal or loss of reception of a signal results in defined operation of the portable battery powered light device 102 such as operating the appliance in an emergency mode in which the light source 116 is operated to generate emergency lighting.

The power regulator 112 can use various techniques for regulating the power supplied to the light source 106. By way of non-limiting example, the power regulator 112 may control power via PWM. In one instance, the power regulator 112 sets the PWM duty cycle to be less than 100%, for example, 80-90 %, or other duty cycle. As such, as the power source 104 drains the duty cycle can be increased to maintain the output power. In another instance, the PWM duty cycle can be kept fixed and the PFM can be employed to regulate the power supplied to the light source 108.

An initial regulated power supplied to the light source 108 can be selected so that an adequate run time or use time is obtained. The inventors appreciate that if the initial regulated power is set too high, the initial emitted light or lumen output may not be maintainable for extended durations, for example, more than 30 seconds, 5 minutes, and the like, hi one example, the initial regulated is selected by referencing a voltage discharge curve, such as those shown infra, and selecting an initial regulated power that can be supplied for a selected duration. For example, the PFM can be initially set so that less than 100% of the pulses are passed to the light source 108, wherein more and more pulses are passed to the light source 108 as the power source 104 drains. By way of example, when a voltage of the power source 104 drops, the internal reference voltage of the PFM drops, resulting in a decreasing current, which results in an increase in the PFM, for example, by adjusting the PWM ratio of on to off, in order to maintain the current output lumen level. In another example, a variable resistor may be used to regulate power output, wherein the resistance is decreased as the power source 104 drains to maintain the output power.

FIGURE 2 shows an example embodiment 200 in which a lumen detector 202 such as one or more photosensors are positioned so as to receive light from one or more light sources of the light source 108. The lumen detector 202 produces a signal indicative of the lumen level. The signal is fed back or provided to the power regulator 112, which regulates the power output based on the signal.

The lumen detector (202) does not necessarily need to be a separate component in the appliance. For example, the lumen detector 202 can utilize the relationship between LED junction forward voltage and temperature to determine a temperature by sensing the voltage across the LED. Then, the relationship between temperature and lumen output can be utilized to determine a lumen output from the determined temperature. Thus, the lumen output can be determined by measuring the LED junction forward voltage. For example, a typical white LED can have a junction forward voltage of 3.45 volts when LED junction temperature equals to the ambient temperature of 25c, achieving 100 lumen at about 350 mA current passing through it. The LED lumen drops to 80 lumen at the same 350 mA current passing through it, when the junction temperature raised to 75c at the same ambient temperature of 25 c. At this operation conditions, we found the forward voltage to be 3.2 Volts. The difference of the 0.25 volts is an indication of the LED junction temperature. With prior knowledge of the relationship between the lumen and the junction temperature, we can further know how much lumen drop because of the variation the temperature, then adjust the current through the LED to compensate for such lumen drop to maintain the lumen output.

FIGURE 3 shows an example embodiment 300 in which a current sensor 302 such as a resistor is used to monitor power output, for example, by sensing the current supplied to the light source 108. In this instance, the power regulator 112 regulates the power output based on sensed current.

A controller, such as controller 816, can interpret the sensed current and determine adjustments to compensate for variations in the sensed current. In one example, the PWM of the regulated power is adjusted to compensate for lower sensed current.

FIGURE 4 shows an example embodiment 400 in which a voltage sensor 504 senses a voltage output of the regulator 112. In this instance, the power regulator 112 regulates the power output based on the sensed voltage.

A controller, such as controller 816, can interpret the sensed voltage output and adjust the regulated power in response. For example, the duty cycle of PWM can be increased to compensate for a lower sensed voltage output. FIGURE 5 shows an example embodiment 500 in which the power regulator 112 regulates the output power based on a corresponding power source voltage discharge curve 502, which is used to approximate a current state of the power source as a function of usage. The power source 104, in this example, is a battery power source that has a varying voltage output depending on several factors including, but not limited to, load, capacity, battery chemistry and the like.

Generally, the current through a battery is not a fixed value and depends on the external loads. The situation is further complicated utilizing LED(s) as the light source 108 because the load to the LED depends on the operations mode, and it can vary. For example, in regulated current mode operation, the current through the LED is a constant value, the forward voltage will continue drop according to the time constant of the thermal properties of the system until the LED temperature reach equilibrium value, then the forward voltage and current stay the same, and the load will not change further. After this point, the load to the system can be a constant. The voltage drops through the battery internal resistance and other chemical factors have stabilized as well, the voltage across the battery will continuously drop due to capacity of the battery drop. Such drop are typically slower process than the load variation, can be compensated for periodically through adjusting the PWM ratio to compensate for the battery discharge curve.

When chemistry information is not available, the current is set according to the lower supply power. In the case of either alkaline or lithium, we will follow the curve of alkaline.

On the other hand, if we just use the voltage sensing of the output, then the battery sensing is not need. We just need to make the output voltage a constant, therefore the current to the LEDs.

Examples of discharge curves for lithium and alkaline chemistries are shown in Figures 9 and 10. A controller, such as controller 816, can track the voltage output and adjust the regulated power in response. FIGURE 6 shows an example embodiment 600 in which a battery state determiner

602 determines the state of the power source 104, and the regulator 112 regulates the output power based on the determined state.

The battery state determiner 602 can be incorporate into or operate in addition to a controller, such as controller 816. The determiner 602 determines the state of the battery powered source 104 by one or more of several possible mechanisms. For example, the determiner 602 can track usage over time and determine current and future voltage and current characteristics for the battery powered source. Once determined, the determiner 602 can cause the regulated power supplied to the light source 108 to be adjusted to compensate for the current and or future characteristics. FIGURE 7 illustrates a method. At 702, the power supplied to the light source 108 is regulated so that less than 100% of the available power or available battery power is supplied to the light source 108. As described herein, this can be achieved through PWM, PFM, both and/or otherwise. The light source 108 provides light, measurable in lumens, in response to the power supplied, also referred to as received power. Generally, the higher the received power, the greater the light output. The light source 108 has a light source voltage, for example, a voltage across an LED, and a light source current, for example the current flowing through the light source. It is appreciated that the light source voltage and/or current can be measured and/or calculated based on other measurements. For example, voltage directly sensing by the Microprocessor, voltage sensing across a current sensing resistor for the current value.

At 704, the regulated power is monitored as described herein. Generally, feedback is obtained and analyzed. The feedback can be obtained continuously and/or periodic time periods. The feedback includes information including, but not limited to, battery chemistry, internal resistance, battery voltage under load, open circuit battery voltage, temperature, measured light output, discharge curve, remaining capacity, estimated light output, current through the light source 108, voltage across the light source 108, and the like.

In one example, the power supplied to the light source 108 is monitored by measuring a sense resistor proximate the light source 108. In another example, the power supplied to the light source 108 is monitored by measuring voltage across the light source. At 706, it is determined whether the power supplied to the light source 108 should be adjusted. For example, in order to maintain a substantially constant lumen output or otherwise, power supplied to the light source 108 may need to be increased. In one example, a measurement from a sense resistor is compared with a reference value to determine if an adjustment is needed. In another example, the voltage of the light source is compared with a previous value or a reference value to determine if an adjustment is needed. As a result, the power supplied to the light source is relatively constant, whereas the power from the battery may not be constant, such as shown in Figure 12.

If the power supplied to the light source does not need to be adjusted, 704 is repeated. If so, then at 706 the output power is adjusted, and act 704 is repeated.

PFM is a specific case of PWM to control the power to the load, it can adjust the on and off ratio through a fixed high frequency pulse train through selectively passing or skipping certain pulses, therefore, it has a limited maximum ratio that is determined by the on off ratio of the individual pulse, as well as system response time. PWM is typically operate power to the load through adjust the on off ratio. One can combine the two systems together to add flexibility in engineering design, to avoid the dependency on the chip manufacturing.

It is appreciated that adjustments performed at 706 may need to be performed iteratively in order to adjust the power supplied to the light source to an acceptable level or threshold amount. For example, a voltage variation of 0.10 volts across an LED light source from a reference or initial value (e.g., 3.2 volts), may result in increasing a duty cycle of PWM supplied to the light of 1%. The increase in duty cycle, in this example, reduces the voltage variation to 0.06 volts. If the threshold is set to a variation of 0.03 volts from the initial value (e.g., range of 3.17 to 3.23), another adjustment is needed, resulting in an increase of the PWM duty cycle by 1%, that then yields a voltage variation of 0.02 volts, which is acceptable in this example.

An initial regulated power supplied to the light source 108 can be selected so that an adequate run time or use time is obtained. It is appreciated that available power decreases over time for battery power sources. Further, it is appreciated that if the initial regulated power is set too high, the initial emitted light or lumen output may not be maintainable for extended durations, for example, more than 30 seconds, 5 minutes, and the like. The reason is that the available power, for example from a battery power source, decreases over time limiting the ability to adjust power. In one example, the initial regulated power is selected by referencing a voltage discharge curve, such as those shown in Figures 9 and 10, and selecting an initial regulated power that can be supplied for a selected duration. In another example, the initial regulated power is selected to a percentage below an initial available power.

The lighting appliance can be any type of light appliance including, but not limited to, a battery powered portable hand held flashlight, headlight that affixes to a helmet or a strap wearable around the head of a human, lantern, pendent light, floor light, table light, etc. and/or other lighting appliance.

Figure 8 is a block diagram of a lighting appliance in accordance with an aspect of the invention. The appliance of Figure 8 can be incorporated with or utilize above aspects of the various figures. The appliance includes a battery power source 104, a power regulator 112, a light source 108, and a controller 816.

The battery power source 104 supplies battery power. The battery power source 104 is similar to the power source 104 described supra. Additionally, the battery power source can be of a particular chemistry, alkaline, nickel-metal hydride, lithium, lithium ion, and the like. The battery power source 104 has associated characteristics including, but not limited to, discharge curve, open circuit voltage, load voltage, capacity, internal resistance, chemistry, and the like. The power regulator 112 is similar to the power regulator 112 described supra. The power regulator 112 receives the battery power from the battery source 104 and supplies regulated power to the light source 108. The regulated power is controlled such that the light source 108 emits selected or substantially constant light, which may be specified as lumen output.

The controller 816 receives feedback from the light source 108 and/or the battery power source 104 and controls the power regulator 112 so that the regulated power supplied to the light source 108 emits selected light amount or substantially constant light. Additionally, the controller 816 can determine an initial regulated power output for the power regulator that will permit adjustments to compensate for temperature and/or variations of the battery power source 104.

Figure 9 is a circuit diagram illustrating a lighting appliance in accordance with an aspect of the invention. The appliance is described with specific electronic components for illustrative purposes only. The appliance provides a substantially constant light output by regulating power to a light source 108.

A battery power source 104 supplies power to a regulator 112. The regulator supplies regulated power to a light source 108, shown in this example as an LED. In one example, the regulator 112 utilizes pulse width modulation to adjust power and/or current to the light source 108. A sense resistor 920 is coupled to the light source 108 and provides a sensed voltage. A comparator/controller 816 compares the sensed voltage with a reference voltage and supplies an adjustment value to the regulator 112.

Figures 10, 11, and 12 are graphs illustrating operation of a lighting appliance, such as the appliance described with reference to Figure 9. The figures illustrate how battery power, battery current, and battery voltage vary in order to supply substantially constant power to an LED as a light source and, in turn, provide substantially constant light output. Examples of components employed to generate the below figures are listed.

A high power surface mounted sense resistor having a resistance of 0.055 ohms is employed for 920. A micro-controller from Microchips that performs PWM is used as a power regulator 112. A feedback differential amplifier is employed as controller 816 to identify the difference between the reference voltage and the sensed current value, were integrated with the PWM controller. The battery employed as the power source 104 is an Energizer L91, having a chemistry of Lithium/Iron Disulfide (Li/FeS2). The light source 108 used a Lumiled Rebel LED. The above example components are provided for illustrative purposes only and it is appreciated that the invention is not limited to the above and includes other suitable components.

Figure 10 shows current from a battery source over time. An x-axis depicts time in hours and a y-axis depicts currents in mA. It can be seen that current increases over time in order to facilitate a substantially constant power to be supplied to an LED light source. Figure 11 shows battery voltage over time. An x-axis depicts time in hours and a y-axis depicts battery voltage in volts. The battery voltage is measured across a single battery and it can be seen that it decreases as the battery is discharged. Figure 12 illustrates battery power over time. An x-axis depicts time in hours and a y-axis depicts battery power in mW. It can be seen that the battery power increases over time in order to yield substantially constant power to the LED light source. Thus, the relationship between power supplied to the LED light source and battery power is not linear: even the power to the LED is a constant, the power drawn from the battery is not a constant. As the battery voltage decreases with remaining capacity during discharge, the amount of battery power utilizes to maintain light output increases. Other approaches merely attempt to utilize constant battery power: when battery voltage drop, the current draw from battery is risen, so as the product of the two will yield a constant current. The reason the LED power is not a constant when the power drawn from battery is a constant is because: when the current drawn from the battery increase, the power consumed by the battery increased, partly because more current pass through the internal resistor of the battery, and other power dissipation factor, such as battery chemistry. The more current was drawn from the battery, then the more current flow through the circuitry in between the battery and the light source. The PWM circuitry typically has limited efficiency, it will increase the circuitry power dissipation as well. These additional power dissipations lead to less than the desired power supply to the LED, need to be account for to have a true constant power supply to the LED.

Figure 13 is a graph illustrating discharge curves for AA lithium and AA alkaline batteries. The curves show low drain performance at a current of 50mA. The x-axis depicts service hours and the y axis depicts voltage (closed circuit voltage (CCV)).

Figure 14 is a graph illustrating discharge curves for AA lithium and AA alkaline batteries. The curves show high drain performance at a current of 100OmA.

The x-axis depicts service hours and the y axis depicts voltage (closed circuit voltage (CCV)).

Modifications and alterations will occur to others upon reading and understanding the preceding description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims and the equivalents thereof.

Claims

CLAIMS What is claimed is:

1. A lighting appliance, comprising: a contact (102) that receives battery power from a battery power source; a light source (108) that emits light; and a power regulator (112) that receives the battery power and selectively supplies regulated power to the light source according to feedback, wherein the feedback includes battery characteristics and light source characteristics.

2. The lighting appliance of claim 1, wherein the power regulator (112) regulates the received power so as to maintain a substantially constant lumen output when the voltage of the battery power decreases.

3. The lighting appliance of any one of claims 1-2, further including a lumen detector (202) that detects the emitted light and the feedback further includes the detected emitted light.

4. The lighting appliance of any one of claims 1-3, further including a current sensor (302, 920) that senses the current supplied to the light source (108) and the feedback further includes the sensed current.

5. The lighting appliance of any one of claims 1-4, further including a voltage sensor (504) that senses a voltage output across the light source and the feedback further includes the voltage output across the light source 108.

6. The lighting appliance of any one of claims 1-5, wherein the power regulator (112) further regulates the output power based on a corresponding power source voltage discharge curve (502) of the power source.

7. The lighting appliance of any one of claims 1-6, further including power source state determiner (602) that determines a state of the power source, wherein the power regulator (112) regulates the output power based on the determined state.

8. The lighting appliance of any one of claims 1-7, wherein the power regulator (112) regulates the output power using pulse width modulation.

9. The lighting appliance of any one of claims 1-8, wherein the power regulator regulates the output power using pulse frequency modulation.

10. The lighting appliance of any one of claims 1-9, further comprising a differential amplifier 816, a sense resistor 920, and a reference voltage, wherein a voltage across the sense resistor is compared with the reference voltage by the differential amplifier 816 to generate a signal as feedback to the power regulator 112.

11. The lighting appliance of any one of claims 1-10, wherein the battery power source comprises a battery having lithium/iron disulfide chemistry.

12. The lighting appliance of any one of claims 1-11, wherein the light source includes one or more of an incandescence, electroluminescence, gas discharge, at least one LED, or high intensity based light source.

13. The lighting appliance of any one of claims 1-12, wherein the power regulator 112 supplies an initial regulated power less than an available regulated power.

14. The lighting appliance of any one of claims 1-13, further comprising a controller 816 that controls operation of the power regulator 112.

15. The lighting appliance of any one of claims 1-14, further comprising a controller 816 that receives feedback regarding the battery power source 104 and feedback regarding the light source 108.

16. The lighting appliance of any one of claims 1-15, further including an interface for operating the appliance alternatively in two or more different modes of operation.

17. The lighting appliance of any one of claims 1-16, further comprising a lumen detector 202 that measures a junction forward voltage of the light source to determine lumen output.

18. A method, comprising: regulating power supplied by a battery power source to a light source (108) so that less than 100% of initial available power is supplied to the light source (702); measuring characteristics of the light source (704); maintaining a lumen level of an output of the light source by adjusting the regulated power (706) according to the measured characteristics.

19. The method of claim 18, further comprising measuring lumen output from the light source and wherein the measured characteristics further include measured lumen output.

20. The method of any one of claims 18-19, further comprising measuring current drawn by the light source and wherein the measured characteristics further include current drawn.

21. The method of any one of claims 18-20, wherein the regulated power is further adjusted as the power source capacity decreases.

22. The method of any one of claims 18-21 , wherein adjusting the regulated power includes utilizing pulse width modulation.

23. The method of any one of claims 18-22, further comprising selecting an initial regulated power according to one or more use factors.

24. The method of any one of claims 18-23, wherein the one or more use factors include at least one of the following: constant output use time, selected lumen output, remaining capacity, and battery chemistry.

25. The method of any one of claims 18-24, further comprising measuring a temperature of the light source and wherein the measured characteristics include the measured temperature.

26. The method of any one of claims 18-25, wherein the measured characteristics include at least one of LED temperature rise and droop effect.

27. The method of any one of claims 18-26, wherein adjusting the regulated power includes adjusting a voltage output according to a temperature of the light source and current drawn by the light source.

28. The method of any one of claims 18-27, wherein adjusting the regulated power includes adjusting current supplied to the light source.

29. The method of any one of claims 18-28, wherein the regulated power supplied to the light source is initially 10 percent below the initial available power.