Hybrid control of a variable brightness of an optical component

Abstract

Disclosed herein are systems, devices, and methods for adjusting the emitted brightness levels of an optical component, such as a light-emitting diode. The system allows for adjusting the drive current of the optical component so as to provide a dynamic range of effective brightness levels emitted from an optical component. A modulation circuit is connected to a supply circuit, where the modulation circuit controls the supply circuit to switch the drive current between two different current levels, wherein one of the two different current levels is at an intermediate current level that is between zero and a maximum drive current that corresponds to a maximum brightness level in the dynamic range of effective brightness levels.

Description

HYBRID CONTROL OF A VARIABLE BRIGHTNESS OF AN OPTICAL COMPONENTCross-Reference to Related

[0001] This application claims priority to German Patent Application No. 10 2023 117 333.2 filed on June 30, 2023, the contents of which are incorporated herein by reference in its entirety.Technical Field

[0002] The disclosure relates generally to adjusting the brightness of an optical component such as a light-emitting diode and, in particular, to adjusting the effectively-visible brightness of the optical component through the use of pulse width modulation of the current supplied to the optical component.Background

[0003] The light output (e.g., brightness of light emitted) from an optical component such as a light-emitting diode (LED) typically relates to the electrical current used to drive the optical component. Using an LED as an example, driving the LED with a higher current typically increases the brightness while driving it with a lower current typically decreases the brightness. This relationship, however, is often non-linear, where an increase in current does not necessarily lead to the same increase in brightness. Moreover, the relationship between drive current and light output may further change based on temperature, aging, and other environmental factors. As a result, pulse width modulation (PWM) is often used to control the effective brightness of the optical component, where the effective brightness is what can be perceived by the human eye while switching the LED on and off at a particular rate. The human eye will perceive an averaged brightness that is proportional to the duty cycle (e.g., the length of time the LED is on compared to the length of time the LED is off during the period of the PWM). For example, the duty cycle may be adjusted so as to change the effective brightness perceived by a typical human eye. Byusing an adjustable duty cycle, a generally linear relationship in the effectively-perceived brightness may be provided by a relatively simple PWM switching circuit that switches the fixed drive current on and off.

[0004] While such a switching circuit may be simple, there are some drawbacks to using PWM to adjust the brightness of an optical component such as an LED. For example, using PWM may emit high levels of electromagnetic radiation (EMR) from switching, and typical measures to mitigate the switching transients (e.g., using slew rate control to “soften” the switch) may add costly complexity. In addition, switching transients from PWM may also introduce non-linearities in the PWM drivers that may need to be mitigated, especially in high-precision drivers for red- green-blue (RGB) LEDs. Another downside of PWM is that the human eye may perceive a “flicker” at low frequencies, especially where the light source is moving (e.g., a vehicle whose brake lights use LEDs that are brightness-adjusted via a PWM scheme). Higher frequencies (e.g., greater than 2 kHz) may be helpful in mitigating perception of flicker, but this, in turn may lead to increased EMR from switching transients. In addition, power efficiency of PWM may be poor, especially at low duty cycles and a high current level, where the LED may be operating in a droop range (e.g., especially for green / blue LEDs).Brief Description of the Drawings

[0005] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the exemplary principles of the disclosure. In the following description, various exemplary aspects of the disclosure are described with reference to the following drawings, in which:FIGs. 1 A and IB each show an exemplary PWM-alone approach for adjusting the brightness of an optical component;FIGs. 2A and 2B each illustrate an exemplary hybrid PWM control system for adjusting the brightness of an optical component;FIG. 3 depicts an exemplary PWM-only approach that may be used to set different effective / perceived brightness levels;FIG. 4 depicts exemplary hybrid PWM control system for adjusting the brightness of an optical component that may be used to set different effective / perceived brightness levels;FIG. 5 depicts an example of where the minimum step size between adjacent available current levels for a hybrid PWM control system is larger than a minimum threshold current level;FIG. 6 illustrates an example of where the hybrid PWM control system may avoid selecting intermediate current levels that fall below a minimum threshold current level;FIG. 7 illustrates an example graph of a relationship among modulation index, frequency, and perceptible flicker when PWM is used to drive an optical component;FIG. 8 shows an example graph of the relationship among modulation index, frequency, and perceptible flicker when PWM is used to drive an optical component;FIG. 9 shows an example relationship between the PWM frequency and eight current settings of the hybrid PWM control system of FIG. 8, each current setting relative to the maximum available current setting;FIG. 10 shows an example relationship between a DAC setting and current;FIG. 11 shows an example relationship characterizing an optical component that relates brightness to drive current;FIG. 12 shows an example of an example relationship between a setting of a digital to analog converter (DAC) and brightness; andFIG. 13 depicts an exemplary schematic flow diagram of a method for a hybridPWM control system.Description

[0006] The following detailed description refers to the accompanying drawings that show, by way of illustration, exemplary details and features.

[0007] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration”. Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs.

[0008] Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures, unless otherwise noted.

[0009] The phrase “at least one” and “one or more” may be understood to include a numerical quantity greater than or equal to one (e.g. , one, two, three, four, [...], etc. , wheremeans that such a series may continue to any higher number). The phrase “at least one of’ with regard to a group of elements may be used herein to mean at least one element from the group consisting of the elements. For example, the phrase “at least one of’ with regard to a group of elements may be used herein to mean a selection of: one of the listed elements, a plurality of one of the listed elements, a plurality of individual listed elements, or a plurality of a multiple of individual listed elements.

[0010] The words “plural” and “multiple” in the description and in the claims expressly refer to a quantity greater than one. Accordingly, any phrases explicitly invoking the aforementioned words (e.g, “plural [elements]”, “multiple [elements]”) referring to a quantity of elements expressly refers to more than one of the said elements. For instance, the phrase “a plurality” may be understood to include a numerical quantity greater than or equal to two (e.g, two, three, four, five, [...], etc., where “[...]” means that such a series may continue to any higher number).

[0011] The phrases “group (of)”, “set (of)”, “collection (of)”, “series (of)”, “sequence (of)”, “grouping (of)”, etc., in the description and in the claims, if any, refer to a quantity equal to or greater than one, i.e., one or more. The terms “proper subset”, “reduced subset”, and “lessersubset” refer to a subset of a set that is not equal to the set, illustratively, referring to a subset of a set that contains less elements than the set.

[0012] The term “data” as used herein may be understood to include information in any suitable analog or digital form, e.g., provided as a file, a portion of a file, a set of files, a signal or stream, a portion of a signal or stream, a set of signals or streams, and the like. Further, the term “data” may also be used to mean a reference to information, e.g., in form of a pointer. The term “data”, however, is not limited to the aforementioned examples and may take various forms and represent any information as understood in the art.

[0013] The terms “processor” or “controller” as, for example, used herein may be understood as any kind of technological entity that allows handling of data. The data may be handled according to one or more specific functions executed by the processor or controller. Further, a processor or controller as used herein may be understood as any kind of circuit, e.g., any kind of analog or digital circuit. A processor or a controller may thus be or include an analog circuit, digital circuit, mixed-signal circuit, logic circuit, processor, microprocessor, Central Processing Unit (CPU), Graphics Processing Unit (GPU), Digital Signal Processor (DSP), Field Programmable Gate Array (FPGA), integrated circuit, Application Specific Integrated Circuit (ASIC), etc., or any combination thereof. Any other kind of implementation of the respective functions, which will be described below in further detail, may also be understood as a processor, controller, or logic circuit. It is understood that any two (or more) of the processors, controllers, or logic circuits detailed herein may be realized as a single entity with equivalent functionality or the like, and conversely that any single processor, controller, or logic circuit detailed herein may be realized as two (or more) separate entities with equivalent functionality or the like.

[0014] The term “optical component” is used herein to broadly encompass any type of device that emits light in response to an applied current. While an LED is often used as an example of such an optical component, reference to an LED is not limiting and the hybrid PWM control system discussed below may be used with any type of optical component.

[0015] As noted above, using PWM to switch on and off a fixed drive current supplied to an optical component such as an LED may provide a relatively simple way of having a brightness- adjustable LED. As discussed in more detail below, the disclosed hybrid PWM control system may help reduce the drawbacks associated with using PWM alone to adjust the brightness of an optical component, drawbacks such as spurious EMR emissions, perceptible flicker, and low power efficiency.

[0016] In particular, a hybrid PWM control system may be used to adjust the brightness of the light output by an LED (e.g., the effective brightness perceived by a human eye), where the drive current to the LED is not switched on and off but rather, switched between two different drive current levels. The difference between the two different drive current levels may be small relative to the full dynamic range of the adjustable light output. For example, multiple pairs of different (e.g., discreet) drive current levels may be selected to cover the full adjustable range of light output, where PWM may be used on the selected pair to interpolate brightness levels between the two different drive current levels of the pair. In this sense, the control scheme may be considered “hybrid,” because it does not rely on PWM alone for brightness control.

[0017] FIGs. 1A and IB illustrate a conventional PWM-only approach for adjusting the brightness of an LED. In order to output a range of brightness levels from the LED, a current driver is switched on and off between a fixed current level 110 (ILED) that drives the LED (e.g., along line 190) and no current that drives the LED (e.g., along line 120). The length of time that the LED is switched on (along line 190) as compared to the length of time it is switched off (along line 120) in a period (e.g., the duty cycle at a particular frequency), sets the effective (e.g., average) light output (between zero and ILED) that is perceived by the human eye (e.g., perceived brightness).

[0018] This perceived brightness may be adjusted over the range of brightness levels by varying the duty cycle. As shown in FIG. 1 A for example, a shorter duty cycle is used (e.g., theLED is switched on for approximately 25% of the frequency period), resulting in a perceivedbrightness 130. To provide a higher effective light output, a longer duty cycle may be used, as shown, for example in FIG. IB. In FIG. IB, the duty cycle has been increased as compared to that of FIG. 1A (e.g., in FIG. IB, the LED is switched on for approximately 60% of the frequency period). The result is a higher perceived brightness 130. Thus, based on the duty cycle (e.g., varied from 0% to 100%), the perceived brightness may be adjusted over the range from zero (at a duty cycle of 0% or always off during the period) to the brightness associated with ILED (at a duty cycle of 100% or always on during the period). In this PWM-only approach, each duty cycle setting corresponds to just one perceived brightness setting, and in order to set a target brightness setting, the corresponding duty cycle is be selected.

[0019] In contrast to the PWM-only approach of FIGs. 1 A and IB, examples of a hybrid PWM control system are shown in FIGs. 2A and 2B. Rather than always switching between driving the LED at a fixed drive current and turning the current off, the hybrid PWM control system determines a pair of current levels between which the LED will be driven, and then uses PWM in order to interpolate perceived brightness between those two levels. One of the current levels of the pair may be an intermediate current level, meaning it is a non-zero current level that is below a maximum drive current at which the LED will be driven (e.g., corresponding to the maximum light output to which the LED will be driven). This allows the difference between the pair of current levels to be smaller than the full range of currents at which the LED may be driven for providing the range of available brightness levels.

[0020] As shown in FIG. 2A, for example, the hybrid PWM control system may select a first current (Ii) and a second current (I2) as the pair of current levels between which the LED will be driven. Then, the hybrid PWM control system may use PWM (e.g., adjusting the duty cycle and / or frequency period) to provide interpolated effective brightness levels between the LED light output at Ii and the LED light output at I2. In FIG. 2A, a perceived brightness 230 (between the LED light output at Ii and the LED light output at I2) may be set by applying a PWM duty cycle of approximately 20% (e.g., the length of time that the LED is driven with a current level of Ii (alongline 211) as compared to the length of time the LED is driven with a current level of I2 (along line 212) in the frequency period). To provide a range of brightness levels between zero and the full brightness associated with ILED, different pairs of current levels may be selected over the range of available currents at which the LED may be driven (e.g., intermediate current values between zero and ILED). An example is shown in FIG. 2B, where, in order to set a perceived brightness level 235 that is higher than the perceived brightness level 230 of FIG. 2A, a different pair of intermediate current levels may be selected whose corresponding light outputs encompass perceived brightness level 235. By applying a duty cycle of approximately 20% (e.g., the length of time that the LED is driven with a current level of I3 (along line 213) as compared to the length of time the LED is driven with a current level of I4 (along line 214) in the frequency period), the light output between this pair of current levels is interpolated to arrive at the perceived brightness 235.

[0021] As can be seen in the examples of FIGs. 1A, IB, and 2A, 2B, the difference between the two current levels of the hybrid PWM control system (FIGs. 2A and 2B) may be smaller than that of the dynamic range of the system, whereas in the PWM-only approach, the drive current is switched over the full dynamic range. The smaller difference between current levels means that fewer switching transients may be produced, reducing the EMI emitted from switching between the two. In addition, the smaller difference between current levels means that the PWM frequency may be reduced, which may provide an even further reduction in the EMI emitted. In addition, the smaller difference between current levels may provide improved power efficiency. Moreover, the hybrid PWM control system may offer a higher dynamic range of light output and / or a higher resolution of brightness settings as compared to that of a PWM-only approach.

[0022] FIG. 3 shows an example of how the PWM-only approach may be used to set a perceived brightness level (examples of which are shown at points 330, 331, 339), while FIG. 4 shows an example of how the hybrid PWM control system may be used to set the same or similar perceived brightness (examples of which are shown at points 430, 431, 499). In each plot ofFIGs. 3 and 4, light output (or perceived brightness, to the extent that PWM is applied at a duty cycle of less than 100%, as discussed above) of the LED is plotted along the y-axis. The x-axis plots the brightness setting used to produce the light output.

[0023] Referring to FIG. 3, the maximum brightness setting (and corresponding to a maximum perceived light output at point 339) is shown at line 310, which corresponds to a supplying the fixed current (ILED) to the LED at 100% PWM duty cycle (e.g., the LED is driven by ILED during the entire length of the period). At the other end of the x-axis, the brightness setting is off and the LED is switched off, corresponding to no light output from the LED. The perceived brightness between the maximum and off are achieved by adjusting, as the brightness setting, the duty cycle of the PWM from 100% (always on during the period) to 0% (always off during the period). In other words, decreasing the brightness setting causes a decrease in the duty cycle and therefore a decrease in the perceived brightness. Thus, to set the brightness to point 330, for example, the duty cycle may be set to approximately 40%, so that the LED is switched between ILED and off, providing an average or effective brightness that is between the maximum brightness and off. To set the brightness to point 331, the duty cycle may be increased to a higher level, approximately 75%, so that the LED is switched with a longer “on” time between ILED and off, providing a higher average or effective brightness.

[0024] In the hybrid PWM control system of FIG. 4, the maximum brightness setting (corresponding to a maximum perceived light output at point 439) is shown at line 410, which corresponds to supplying ILED to the LED at 100% PWM duty cycle (e.g., the LED is driven by ILED during the entire length of the period). The perceived brightness between the maximum brightness setting and off are achieved with a two-part hybrid approach. First, a pair of different current levels are selected for the given brightness setting, one of which is at an intermediate current level (e.g., at least one of the pair is greater than zero and lower than ILED). Second, PWM is applied to the pair of current levels, adjusting the duty cycle of the PWM from 100 % (on duringthe full period) to 0 % (off during the full period) to adjust the effective brightness level between the pair of selected current levels.

[0025] As can be seen, a different pair of current levels may be chosen, depending on the level of light output desired. For example, to set the brightness to point 430, the pair of intermediate current levels 411 and 412 may be selected that encompass point 430. Next, the duty cycle may be adjusted to interpolate between intermediate current levels 411 and 412 so as to arrive at the desired brightness level, which, for the brightness level at point 430, using intermediate current levels 411 and 412, may be a 25% PWM duty cycle. To set the brightness to point 431, a different pair of intermediate current levels may be selected (e.g., current levels 413 and 414) that encompass point 431. Next, the duty cycle may be adjusted to interpolate between intermediate current levels 413 and 414 so as to arrive at the desired brightness level, which, for the brightness level at point 431, using intermediate current levels 413 and 414, may be a 75% PWM duty cycle.

[0026] While it may be advantageous for the hybrid PWM control system to select adjacent intermediate current levels so that the difference between the two currents is smaller (e.g., to improve switching performance, lower EMI emissions, etc.), non-adjacent intermediate current levels may be selected. Thus, to set the brightness to point 430, a different pair of intermediate current levels may be selected (e.g., current levels 411 and 413), and the PWM duty cycle adjusted correspondingly to interpolate between intermediate current levels 413 and 414 so as to arrive at the desired brightness level, which, for the brightness level at point 430, using intermediate current levels 411 and 413, may be a 10% PWM duty cycle. In this manner, the hybrid PWM control system may divide the dynamic range of available brightness levels into different pairs of current levels, and PWM is then used to interpolate between each pair. In the example shown in FIG. 4, seven discreet intermediate current levels between zero and ILED are shown, and any of these may be selected as one of the current levels for each pair. By utilizing multiple different pairs, the full dynamic range of brightness levels may be covered.

[0027] The different intermediate current levels for the hybrid PWM control system may be provided by an adjustable current driver circuit (also called a supply circuit or driver circuit) that is configurable to supply different current levels. For example, a digital to analog converter may convert a digital representation of a current level (e.g., a bit or combination of bits) into an analog current source at the corresponding current level that is then used to drive the LED. The number of available current levels defines the resolution of the current source.

[0028] The PWM may be provided by a modulation circuit (also called a PWM circuit) that modulates between the pair of current levels at a selected duty cycle for a selected frequency. The selection of duty cycle and / or frequency may also be provided by a digital to analog converter, for example, that may convert a digital representation of a duty cycle and / or a frequency into modulation of the current levels with the programmed duty cycle and / or at the programmed frequency. The number of available duty cycle settings defines the resolution of the PWM. In the hybrid PWM control system, the overall resolution is additive of the resolution of the current driver circuit and the resolution of the PWM modulation circuit. For example, in a PWM-only implementation, a PWM modulation circuit with 12 bits of dynamic range means that the overall resolution of the available brightness settings is 12 bits. By contrast, a hybrid PWM control system with 3 bit resolution (e.g., 8 current steps) and a PWM modulation circuit with 12 bits of dynamic range provides an overall 15 bits of dynamic range and 15 bits of resolution. In this sense, the hybrid PWM control system allows for higher resolution or allows for reducing circuit complexity (e.g., lower resolution in the PWM modulation circuit, for example) without sacrificing overall resolution.

[0029] Not only may the hybrid PWM control system provide for improved resolution and / or lower circuit complexity, the hybrid PWM control system may also improve power efficiency due to the fact that the LED need not be driven to the highest current level, as is the case in a PWM- only system, where the maximum current (corresponding to the maximum brightness) is always used to drive the LED, even when the brightness setting is much lower than the maximumbrightness setting. In a hybrid PWM control system, using an intermediate level (e.g., that is lower than the maximum current) means a lower driving current for the LED and may improve current efficiency (QE) and wall plug efficiency in the LED. If the LED has the following characteristics, for example, the hybrid PWM control system may have improved power efficiency as compared to a PWM-only system that drives the LED to 80 mA in the “on” phase of the duty cycle:

[0030] In the above table, “IF” is the current that drives the LED (in mA), “Dimming” is the brightness factor relative to 80 mA, “Phirel” is the emitted light flux (Phi) relative to that at 80 mA, “QE_rel” is the relative power efficiency relative to that at 80 mA, “Vf ’ is the a forward voltage of the LED (in volts), “Vfrel” is the forward voltage relative to 80 mA (=Vf(IF) / Vf(80 mA)), “WPE Rel” is the wall plug efficiency relative to that at 80 mA. Using these characteristics as an example, hybrid PWM control system with 4 step hybrid PWM control may improve power efficiency by more than 16% (QE_rel, relative to the PWM-only system at 80 mA) when using a linear current driver. For a boost / buck converter, more than 30% improvement to power efficiency may be possible.

[0031] As should be understood from the above description, the hybrid PWM control system allows for a wide range of possibilities for selecting the individual pairs of current levels as well as the dynamic range of currents used. As some optical devices such as LEDs may perform inconsistently when driven with a lower current (e.g., also called low current instability), the hybrid PWM control system may select currents to be above a current threshold, above which the low current instabilities are minimized or at an acceptable tolerance. The hybrid PWM controlsystem may implement this in a number of ways. One example is to set the minimum step size between adjacent available current levels (e.g., from which the pairs of current levels are selected) to be larger than the minimum threshold current level (IFMIN). An example of this is shown in FIG. 5, where line 550 indicates the minimum threshold current level (IFMIN), above which the low current instabilities are minimized or at an acceptable tolerance. As shown in FIG. 5, the hybrid PWM control system uses a step size 560 between adjacent current levels that is above IFMIN. Such that the first intermediate current step 511 is above IFMIN.

[0032] Another example of how the hybrid PWM control system may address low current instability is to avoid selecting intermediate current levels that fall below IFMIN. While this may reduce the resolution of the lowest current step (because PWM must be used to interpolate between the lowest step and zero amps), it may prevent lower than desirable currents from being selected as an intermediate current level of the current level pair. An example of this is shown in FIG. 6, where line 650 indicates the minimum threshold current level (IFMIN), above which the low current instabilities are minimized or at an acceptable tolerance. As shown in FIG. 6, the hybrid PWM control system does not use otherwise available current levels 611, 612 when selecting the pairs of current levels between which it may modulate using PWM. Thus, the lowest intermediate current level the hybrid PWM control system may select as one of the current levels for the modulation pair is current level 613.

[0033] As noted earlier, one aspect of using PWM to create an effective brightness level perceived by the human eye is that the human eye may also perceive a “flicker” in the light output caused by the PWM. Perception of flicker is often dependent on a combination of factors including the modulation index of the PWM and frequency period of the PWM. Modulation index of PWM is generally defined as the ratio of the difference in peak to minimum amplitudes of current levels between which the signal is modulated over their sum. Thus, if the peak current is A and the minimum current is B, the modulation index is which may be multiplied by 100% to beexpressed as a percentage. Thus, in a conventional PWM-only system, the modulation index is 1(or 100%, if expressed as a percentage) because the LED is switched on and off at a fixed current level (A), so the ratio is A — 0 / L4 + 0 = 1. At a modulation index of 1, the frequency period usually should be above Ik Hz (ideally 2 kHz or greater) in order to avoid perceptible flicker when using PWM to create an effective brightness level. An example of a relationship between modulation index and frequency is shown in FIG. 7, which depicts an annotated graph of an example relationship between modulation index, frequency, and perceptible flicker.

[0034] The Institute of Electronic and Electrical Engineers (IEEE) has set forth a standard (e.g., IEEE1789) recommending combinations of modulation index and frequency where flicker is unlikely (e.g., in normal environmental conditions) to be perceptible. In FIG. 7, the log of frequency is plotted on the x-axis while the log of the modulation index is plotted as a percentage on the y-axis. The white area to the left indicates modulation index and frequency combinations where flicker caused by PWM is likely to be perceptible. The grey area to the right indicates modulation index and frequency combinations where flicker is likely to be imperceptible. The boundary between the two areas is defined with stepwise functions that relate modulation index to frequency, where between about 8 Hz and 90 Hz, a modulation index that is below 0.025 times the PWM frequency is recommended for imperceptible flicker, and between about 90 Hz and 1 kHz, a modulation index that is below 0.08 times the PWM frequency is recommended for imperceptible flicker. At a modulation index of 1 (100%), the frequency should be above 1 kHz in order to minimize the likelihood of perceptible flicker, whereas at a modulation index below 0.2, the frequency is non-determinative as to perceptible flicker.

[0035] A typical operating point for PWM-only systems is therefore 2 kHz, shown by point 785, because a PWM-only system operates with a modulation index of 1 (100%). If a PWM-only system were to operate at a lower frequency, say 200 Hz, this would fall within the perceptible flicker region, shown at point 745, which would be undesirable. By contrast, a hybrid PWM control system may operate with a lower modulation index due to the use of intermediate current levels. Thus, at a modulation index of about 66% (e.g., in an 8 step system, where the peak is 7and the minimum is 1, the modulation index is (1 — 7) / (l + 7) = 0.667, for example, the hybridPWM control system may be able to operate in the non-perceptible flicker region at 200 Hz, as shown at point 725. As noted earlier, operating at a lower frequency and lower current transient amplitudes may help reduce spurious EMI emissions and related problems. A lower frequency also allows for a lower slew rate to be used for the PWM.

[0036] In this regard, the hybrid PWM control system may also use an adaptive frequency approach where the hybrid PWM control system adjusts the modulation frequency of the PWM based on the currently select pair of different current levels. Thus, the frequency may be reduced when operating at higher current levels (while still avoiding perceptible flicker) and the frequency may be increased when operating at lower current levels (while still avoiding perceptible flicker). FIG. 8, for example, shows, similar to that of FIG. 7, an annotated graph of the relationship among modulation index, frequency, and perceptible flicker where line 800 defines the recommended relationship (e.g., from IEEE 1789) below which the combination of modulation index and frequency should remain in order to avoid perceptible flicker. The points shown with circles (annotated as “2000 Hz PWM”) show the different operating points for the hybrid PWM control system (e.g., one that has eight different pairs of available current levels) that operates at a fixed frequency of 2000 Hz). The points shown with diamonds (annotated as “Adaptive Frequency” points) are example frequency / modulation index combinations that a hybrid PWM control system may use (e.g., one that has eight different pairs of available current levels), where pairs with a lower modulation index may be operated at lower frequencies while still avoiding perceptible flicker. FIG. 9 shows an example relationship of the hybrid PWM control system of FIG. 8 between the eight current settings, each relative to the maximum available current setting, and the variable PWM frequency.

[0037] The hybrid PWM control system may utilize a functional relationship that relates the pair of different current levels to determine a modulation index, and then the frequency may be determined by relating the modulation index to frequency. For example, the percent modulationindex (MI) may be determined by the following formula, where Ii is one current level of the pair and Io is the other current level of the pair:

[0038] Then, the frequency may be determined based on the calculated MI:

[0039] As should be appreciated, while the relationship above is a linear relationship, a nonlinear relationship or any other type of relationship may be used (e.g., one that ensures an imperceptible flicker at each available brightness setting over the dynamic range of the system) to relate frequency to the current level.

[0040] While the recommended combination of modulation index and frequency (e.g., from IEEE 1789) for avoiding perceptible flicker is a generalized recommendation in normal environments, the perception of flicker from a PWM-driven optical component (e.g., an LED) may not only depend on the modulation index and PWM frequency of the light source but may also depend on the ambient conditions in the environment, and more particularly, on the intensity of light emitted from the optical component as compared to the ambient light of the environment. Generally, two situations may be relevant. One is where the LED may be operated in a brightly- lit environment such as in daylight or with artificial lights that generate ambient light. Another situation is where the LED may operate in close vicinity to other light sources that may reduce the modulation contrast at the human eye and may therefore impact perception of flicker.

[0041] To account for the impact of other light sources on perceptible flicker, the hybrid PWM control system may use a level of ambient light (e.g., measured by an ambient light sensor, provided about the environment, etc.) and / or an amount of light emitted by a nearby light source(s) (e.g., from information about other light sources in the vicinity, from a focused light sensor, etc.). Based on the other sources of illumination in the environment, the hybrid PWM control system may apply an offset when calculating the modulation index, and adjust other parameters (e.g.,PWM frequency) accordingly. For example, the hybrid PWM control system may determine modulation index (MI) based on the following equation, where Ii is one current level of the pair , Io is the other current level of the pair, and / um / > is a factor (e.g., a constant) that relates to the other sources of illumination in the environment:

[0042] The hybrid PWM control system may also compensate for non-linearities in the brightness output of the optical component by configuring available set of discrete current levels to be non-linear. For example, as noted above, a digital to analog circuit may be used to provide an available set of discrete current levels. The digital to analog converter may convert a digital representation of a current level (e.g., a bit or combination of bits) into an analog current source at the corresponding current level that is then used to drive the optical component. In particular, the change in current between adjacent current levels may be non-uniform. As one example, a lookup table may be used to define the relationships between brightness setting and corresponding current level / light output. For example, a digital to analog converter may provide 16 different settings, each associated with a different current level output of the current supply circuit that drives the optical component. For example, the delta between the current levels corresponding to the first bit (bit 0) and the second bit (bit 1) may be different from the delta between the current levels corresponding to the fifteenth bit (bit 14) and the sixteenth bit (bit 15), as shown for example in FIG. 10. In FIG. 10, the digital setting (integers from 0 to 15) of the digital to analog converter (DAC) is plotted on the x-axis while the corresponding current level is plotted on the y-axis (from 0 to 140 mA). As can be seen, the relationship between the DAC setting and the corresponding current level is non-linear.

[0043] The hybrid PWM control system may determine the relationship between the digital setting and corresponding current level to be based on, for example, the relationship between the drive current of an optical component and the corresponding brightness (e.g., a brightness of thet * / )LED may be characterized by the equation+where a and b are parameters (e.g., for fit). For example, the brightness of an LED may have a non-linear relationship to its drive current, where the change in brightness decreases as drive current increases, as shown, for example, in the graph of FIG. 11. The hybrid PWM control system may set (as shown in FIG. 10), the relationship between the digital setting and corresponding current level to compensate for the non-linear relationship between the drive current of the LED and its corresponding brightness (as characterized in the graph of FIG. 11).

[0044] In doing so, this may provide a linear relationship between the brightness setting (e.g., the DAC setting) and the brightness level emitted by the LED. Then, the hybrid PWM control system may use PWM between two (adjacent) DAC settings in order to interpolate (as an effective brightness perceived by the user) to provide a linear range across the entire dynamic range of available brightness levels. This linearity may also allow the hybrid PWM control system to directly implement other transfer functions, including, for example, a gamma correction transfer function. As should be appreciated, each type of optical component (e.g., different colors, from different manufacturers, etc.) may impact the relationship between the drive current of the LED and its corresponding brightness, and the hybrid PWM control system may take into account the type of LED (or any measured / provided relationship between drive current and brightness) when determining what current levels correspond to which digital settings for supply current.

[0045] FIG. 13 depicts a schematic flow diagram of a method 1300 for a hybrid PWM control system. Method 1300 may implement any of the features discussed above with respect to the features of hybrid PWM control and any of FIGs. 1-12. Method 1300 includes, in 1310, selecting in response to a brightness setting, a pair of two different current levels from among a plurality of discrete current levels, wherein one of the pair of the two different current levels is an intermediate current level that is above zero and below a maximum current associated with the largest brightness level of the dynamic range of effective brightness levels. Method 1300 also includes, in 1320, modulating between the two different current levels with a modulation duty cycle and / or at amodulation frequency, wherein the modulation duty cycle and / or modulation frequency cause light to be emitted from the LED with an effective brightness corresponding to the brightness setting.

[0046] In the following, various examples are provided that may include one or more aspects described above with reference to the features of the hybrid PWM control discussed above. The examples provided in relation to the devices may apply also to the described method(s), and vice versa.

[0047] Example 1 is a device for providing a dynamic range of effective brightness levels from an optical component, the device including a supply circuit configured to provide a drive current to the optical component. The device also includes a modulation circuit connected to the supply circuit, the modulation circuit configured to control the supply circuit to switch the drive current between two different current levels, wherein one of the two different current levels is nonzero and below a maximum drive current that corresponds to a maximum brightness level in the dynamic range.

[0048] Example 2 is the device of example 1, wherein the zero current level is where no current is supplied to the optical component.

[0049] Example 3 is the device of either of examples 1 or 2, wherein the zero current level is essentially zero amps (e.g., essentially zero for the radiative channel, but may be non-zero for nonradiati ve channels).

[0050] Example 4 is the device of any of examples 1 to 3, wherein the zero current level defines where no light is output from the optical component.

[0051] Example 5 is the device of any of examples 1 to 4, wherein the supply circuit includes a current source.

[0052] Example 6 is the device of any of examples 1 to 5, wherein the optical component includes a light emitting diode.

[0053] Example 7 is the device of any of examples 1 to 6, wherein the modulation circuit is configured to adjust the drive current between the two current levels with a duty cycle and / or at a modulation frequency.

[0054] Example 8 is the device of example 7, wherein the two current levels and the duty cycle and / or modulation frequency define an effective brightness setting within the dynamic range of effective brightness levels for the optical component.

[0055] Example 9 is the device of any of examples 1 to 8, wherein the modulation circuit is configured to adjust the drive current between the current levels at a modulation frequency that is lower than 500 Hz.

[0056] Example 10 is the device of any of examples 1 to 9, wherein the supply circuit is adjustable between a plurality of discrete current levels sufficient to cover the dynamic range of effective brightness levels, wherein the two different current levels include different ones of the plurality of discrete current levels.

[0057] Example 11 is the device of example 10, wherein a magnitude difference between the two different current levels is smaller than a magnitude difference between a smallest of the plurality of the discrete current levels and a largest of the plurality of the discrete current levels.

[0058] Example 12 is the device of example 10, wherein the plurality of discrete current levels increases incrementally by a current step size, wherein a magnitude difference between the first current level and the second current level is the current step size.

[0059] Example 13 is the device of any of examples 1 to 12, wherein the modulation circuit is configured to determine a modulation frequency based on the two current levels, wherein the modulation circuit is configured to adjust the drive current between the two different current levels at the modulation frequency.

[0060] Example 14 is the device of any of examples 1 to 13, wherein the modulation circuit is configured to adjust the drive current between the two current levels at a modulation frequency,wherein the modulation circuit is configured to determine the two current levels based on a target modulation index of the drive current at the modulation frequency.

[0061] Example 15 is the device of example 14, wherein the target modulation index is defined by an amplitude difference between the two current levels divided by a sum of amplitudes of the two current levels.

[0062] Example 16 is the device of either of examples 14 or 15, wherein the modulation circuit is configured to determine the two current levels so that the target modulation index is at or below 0.08 times the modulation frequency, preferably when the modulation frequency is below 1 kHz.

[0063] Example 17 is the device of any of examples 14 to 16, wherein the modulation circuit is configured to determine the two current levels so that the target modulation index is at or below 0.25 times the modulation frequency, preferably when the modulation frequency is below 100 Hz.

[0064] Example 18 is the device of any of examples 14 to 17, wherein the target modulation index is based on an ambient light at the optical component.

[0065] Example 19 is the device of example 18, wherein the device further includes an optical sensor configured to measure the ambient light at the optical component.

[0066] Example 20 is the device of either of examples 18 or 19, wherein the target modulation index is defined by an amplitude difference between the two current levels divided by a sum of an amplitude of the ambient light and amplitudes of the two current levels.

[0067] Example 21 is the device of any of examples 1 to 20, wherein the supply circuit is adjustable between a plurality of discrete current levels that increase from a lowest current level to a highest current level, wherein the two current levels are each higher than the lowest current level.

[0068] Example 22 is the device of any of examples 1 to 21, wherein the supply circuit is adjustable between a plurality of discrete current levels that increase from a lowest current level to a highest current level, wherein the two current levels are selected levels of the plurality ofdiscrete current levels, wherein the selected levels are higher than a threshold minimum current level.

[0069] Example 23 is the device of any of examples 1 to 22, wherein the supply circuit is adjustable between a plurality of discrete current levels that increase incrementally by a current step size, wherein the current step size is larger than a threshold minimum current level.

[0070] Example 24 is the device of either of examples 22 or 23, wherein the threshold minimum current level is based on a characterization of the optical component, wherein preferably the characterization is defined by an average light output degradation over time.

[0071] Example 25 is the device of any of examples 1 to 24, wherein the supply circuit is adjustable between a plurality of discrete current levels that increase incrementally by a variable current step size that varies according to a non-linear function.

[0072] Example 26 is the device of example 25, wherein the non-linear function relates the variable step size to a corresponding brightness emitted by the optical component at each of the plurality of discrete current levels.

[0073] Example 27 is a system for adjusting light emitted by an optical component over a dynamic range of effective brightness levels, the system including a driver circuit configured to supply a drive current to the optical component, wherein a level of the drive current is configurable to a plurality of discrete levels over a current range. The system also includes a pulse width modulation (PWM) circuit configured to cause the driver circuit to modulate the level of the drive current between a pair of two different levels of the plurality of discrete levels, wherein a difference between the two different levels is smaller than the current range of the driver circuit.

[0074] Example 28 is the system of example 27, wherein the PWM circuit is configured to cause the driver circuit to modulate the level of the drive current between the two different levels with a duty cycle that is configurable by the PWM circuit to a plurality of different duty cycles and / or at a frequency that is configurable by the PWM circuit to a plurality of different frequencies, wherein preferably an effective brightness of the optical component is controllable over thedynamic range of effective brightness levels based on a selection of the pair of two different levels and the duty cycle and / or the frequency.

[0075] Example 29 is the system of example 28, wherein the selection of the two different levels for the pair sets a baseline range of light output of the optical component defined by the two different levels, wherein an adjustment to the duty cycle and / or frequency adjusts an effective brightness of the optical component within the baseline range of light output.

[0076] Example 30 is the system of example 29, wherein the baseline range of light output is smaller than the effective dynamic range of effective brightness levels provided by the system.

[0077] Example 31 is the system of any of examples 27 to 30, wherein the PWM circuit includes a digital to analog circuit configured to convert a digital input corresponding to a predefined brightness level within the dynamic range of effective brightness levels into an indication of the two different levels.

[0078] Example 32 is the system of any of examples 27 to 31, wherein each of the plurality of discrete levels represents a corresponding light output of the optical component, wherein a difference between corresponding light outputs of the two different levels is smaller than a dynamic range of corresponding light outputs of the plurality of discrete levels.

[0079] Example 33 is the system of any of examples 27 to 32, wherein the optical component includes a light emitting diode.

[0080] Example 34 is the system of any of examples 27 to 33, wherein the PWM circuit is configured to modulate the level of the drive current between the pair of two different levels with a duty cycle and / or at a modulation frequency.

[0081] Example 35 is the system of example 34, wherein the pair of two different levels and the duty cycle and / or modulation frequency define an effective brightness setting within the dynamic range of effective brightness levels for the optical component.

[0082] Example 36 is the system of any of examples 27 to 35, wherein the PWM circuit is configured to adjust the drive current between the pair of two different levels at a modulation frequency that is lower than 500 Hz.

[0083] Example 37 is the system of any of examples 27 to 36, wherein the pair of two different levels are sufficient to cover the dynamic range of effective brightness levels, wherein the pair of two different levels include different ones of the plurality of discrete current levels.

[0084] Example 38 is the system of any of examples 27 to 37, wherein a magnitude difference between the pair of two different levels is smaller than a magnitude difference between a smallest of the plurality of discrete levels and a largest of the plurality of discrete levels.

[0085] Example 39 is the system of any of examples 27 to 38, wherein the plurality of discrete levels increases incrementally by a current step size, wherein a magnitude difference between a first current level and a second current level of the pair of two different levels is the current step size.

[0086] Example 40 is the system of any of examples 27 to 39, wherein the PWM circuit is configured to determine a modulation frequency based on the pair of two different levels, wherein the PWM circuit is configured to adjust the drive current between the pair of two different levels at the modulation frequency.

[0087] Example 41 is the system of any of examples 27 to 40, wherein the PWM circuit is configured to adjust the drive current between the pair of two different levels at a modulation frequency, wherein the PWM circuit is configured to determine the pair two different levels based on a target modulation index of the drive current at the modulation frequency.

[0088] Example 42 is the system of example 41, wherein the target modulation index is defined by an amplitude difference between the pair of two different levels divided by a sum of amplitudes of the pair of two different levels.

[0089] Example 43 is the system of either of examples 41 or 42, wherein the PWM circuit is configured to determine the pair of two different levels so that the target modulation index is at orbelow 0.08 times the modulation frequency, preferably when the modulation frequency is below 1 kHz.

[0090] Example 44 is the system of any of examples 41 to 43, wherein the PWM circuit is configured to determine the pair of two different levels so that the target modulation index is at or below 0.25 times the modulation frequency, preferably when the modulation frequency is below 100 Hz.

[0091] Example 45 is the system of any of examples 41 to 44, wherein the target modulation index is based on an ambient light at the optical component.

[0092] Example 46 is the system of example 45, wherein the system further includes an optical sensor configured to measure the ambient light at the optical component.

[0093] Example 47 is the system of either of examples 45 or 46, wherein the target modulation index is defined by an amplitude difference between the pair of two different levels divided by a sum of an amplitude of the ambient light and amplitudes of the pair of two different levels.

[0094] Example 48 is the system of any of examples 27 to 47, wherein the plurality of discrete levels that increase from a lowest current level to a highest current level, wherein the pair of two different levels are each higher than the lowest current level.

[0095] Example 49 is the system of any of examples 27 to 48, wherein the plurality of discrete levels increase from a lowest current level to a highest current level, wherein the pair of two different levels are higher than a threshold minimum current level.

[0096] Example 50 is the system of any of examples 27 to 49, wherein the plurality of discrete levels increase incrementally by a current step size, wherein the current step size is larger than a threshold minimum current level.

[0097] Example 51 is the system of either of examples 49 or 50, wherein the threshold minimum current level is based on a characterization of the optical component, wherein preferably the characterization is defined by an average light output degradation over time.

[0098] Example 52 is the system of any of examples 27 to 51, wherein the plurality of discrete levels increase incrementally by a variable current step size that varies according to a non-linear function.

[0099] Example 53 is the system of example 52, wherein the non-linear function relates the variable step size to a corresponding brightness emitted by the optical component at each of the plurality of discrete levels.

[0100] Example 54 is a method of adjusting light emitted by an optical component over a dynamic range of effective brightness levels, the method including selecting in response to a brightness setting, a pair of two different current levels from among a plurality of discrete current levels, wherein one of the pair of the two different current levels is an intermediate current level that is above zero and below a maximum current associated with the largest brightness level of the dynamic range of effective brightness levels. The method also includes modulating between the two different current levels with a modulation duty cycle and / or at a modulation frequency, wherein the modulation duty cycle and / or modulation frequency cause light to be emitted from the optical component with an effective brightness corresponding to the brightness setting.

[0101] Example 55 is the method of example 54, wherein one of the pair is above a zero current level and below a maximum of the plurality of discrete current levels.

[0102] Example 56 is the method of any of examples 54 to 55, wherein the optical component includes a light emitting diode.

[0103] Example 57 is the method of any of examples 54 to 56, wherein the modulating includes adjusting the drive current between the pair of two different current levels with a duty cycle and / or at a modulation frequency.

[0104] Example 58 is the method of example 57, wherein the pair of two different current levels and the duty cycle and / or modulation frequency define an effective brightness setting within the dynamic range of effective brightness levels for the optical component.

[0105] Example 59 is the method of any of examples 54 to 58, wherein the modulating includes adjusting between the two different current levels at a modulation frequency that is lower than 500 Hz.

[0106] Example 60 is the method of any of examples 54 to 59, wherein a magnitude difference between the pair of two different current levels is smaller than a magnitude difference between a smallest of the plurality of the discrete current levels and a largest of the plurality of the discrete current levels.

[0107] Example 61 is the method of any of examples 54 to 60, wherein the plurality of discrete current levels increases incrementally by a current step size, wherein a magnitude difference between a first current level of the plurality of discrete current levels and a second current level of the plurality of discrete current levels is the current step size.

[0108] Example 62 is the method of any of examples 54 to 61, wherein the modulating includes determining a modulation frequency based on the pair two different current levels, wherein the modulating further includes adjusting between the pair of two different current levels at the modulation frequency.

[0109] Example 63 is the method of any of examples 54 to 62, wherein the modulating includes adjusting between the pair of two different current levels at a modulation frequency, wherein the modulating includes determining the pair of two different current levels based on a target modulation index at the modulation frequency.

[0110] Example 64 is the method of example 63, wherein the target modulation index is defined by an amplitude difference between the pair of two different current levels divided by a sum of amplitudes of the pair of two different current levels.

[0111] Example 65 is the method of either of examples 63 or 64, wherein the modulating includes determining the pair of two different current levels so that the target modulation index is at or below 0.08 times the modulation frequency, preferably when the modulation frequency is below 1 kHz.

[0112] Example 66 is the method of any of examples 63 to 65, wherein the modulating includes determining the pair of two different current levels so that the target modulation index is at or below 0.25 times the modulation frequency, preferably when the modulation frequency is below 100 Hz.

[0113] Example 67 is the method of any of examples 63 to 66, the method further including determining the target modulation index based on an ambient light at the optical component.

[0114] Example 68 is the method of example 67, wherein the method further includes measuring (e.g., via an optical sensor) the ambient light at the optical component.

[0115] Example 69 is the method of either of examples 67 or 68, wherein the target modulation index is defined by an amplitude difference between the pair of two different current levels divided by a sum of an amplitude of the ambient light and amplitudes of the pair of two different current levels.

[0116] Example 70 is the method of any of examples 54 to 69, wherein the plurality of discrete current levels increase from a lowest current level to a highest current level, wherein the pair of two current levels are each higher than the lowest current level.

[0117] Example 71 is the method of any of examples 54 to 70, wherein the supply circuit is adjustable between a plurality of discrete current levels that increase from a lowest current level to a highest current level, wherein the pair of two different current levels are higher than a threshold minimum current level.

[0118] Example 72 is the method of any of examples 54 to 71 , wherein the plurality of discrete current levels increase incrementally by a current step size, wherein the current step size is larger than a threshold minimum current level.

[0119] Example 73 is the method of either of examples 71 or 72, the method further including determining the threshold minimum current level based on a characterization of the optical component, wherein preferably the characterization is defined by an average light output degradation over time.

[0120] Example 74 is the method of any of examples 54 to 73, wherein the plurality of discrete current levels increase incrementally by a variable current step size that varies according to a nonlinear function.

[0121] Example 75 is the method of example 74, wherein the non-linear function relates the variable step size to a corresponding brightness emitted by the optical component at each of the plurality of discrete current levels.

[0122] While the disclosure has been particularly shown and described with reference to specific aspects, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims. The scope of the disclosure is thus indicated by the appended claims and all changes, which come within the meaning and range of equivalency of the claims, are therefore intended to be embraced.

Claims

CLAIMSClaimed is:

1. A device for providing a dynamic range of effective brightness levels from an optical component, the device comprising: a supply circuit configured to provide a drive current to the optical component; and a modulation circuit connected to the supply circuit, the modulation circuit configured to: control the supply circuit to switch the drive current between two different current levels; adjust the drive current between the two current levels at a modulation frequency; and determine the two current levels based on a target modulation index of the drive current at the modulation frequency wherein one of the two different current levels is non-zero and below a maximum drive current that corresponds to a maximum brightness level in the dynamic range.

2. The device of claim 1, wherein the optical component comprises a light emitting diode.

3. The device of either of claims 1 or 2, wherein the modulation circuit is configured to adjust the drive current between the two current levels with a duty cycle and / or at a modulation frequency, wherein preferably the two current levels and the duty cycle and / or modulation frequency define an effective brightness setting within the dynamic range of effective brightness levels for the optical component.

4. The device of any of claims 1 to 3, wherein the supply circuit is adjustable between a plurality of discrete current levels sufficient to cover the dynamic range of effective brightness levels, wherein the two different current levels comprise different ones of the plurality of discrete current levels.

5. The device of claim 4, wherein a magnitude difference between the two different current levels is smaller than a magnitude difference between a smallest of the plurality of the discrete current levels and a largest of the plurality of the discrete current levels.

6. The device of claim 4, wherein the plurality of discrete current levels increases incrementally by a current step size, wherein a magnitude difference between the first current level and the second current level is the current step size.

7. The device of any of claims 1 to 6, wherein the modulation circuit is configured to determine a modulation frequency based on the two current levels, wherein the modulation circuit is configured to adjust the drive current between the two different current levels at the modulation frequency.

8. The device of any of claims 1 to 7, wherein the target modulation index is defined by an amplitude difference between the two current levels divided by a sum of amplitudes of the two current levels.

9. The device of any of claims 1 to 8, wherein the modulation circuit is configured to determine the two current levels based on a target modulation index of the drive current at the modulation frequency, wherein the target modulation index is based on an ambient light at the optical component.

10. The device of claim 9, wherein the device further includes an optical sensor configured to measure the ambient light at the optical component, wherein the device further includes an optical sensor configured to measure the ambient light at the optical component.

11. The device of any of claims 1 to 10, wherein the supply circuit is adjustable between a plurality of discrete current levels that increase from a lowest current level to a highest current level, wherein the two current levels are each higher than the lowest current level.

12. The device of any of claims 1 to 11, wherein the supply circuit is adjustable between a plurality of discrete current levels that increase from a lowest current level to a highest current level, wherein the two current levels are selected levels of the plurality of discrete current levels, wherein the selected levels are higher than a threshold minimum current level.

13. The device of any of claims 1 to 12, wherein the supply circuit is adjustable between a plurality of discrete current levels that increase incrementally by a current step size, wherein the current step size is larger than a threshold minimum current level.

14. The device of either of claims 12 or 13, wherein the threshold minimum current level is based on a characterization of the optical component, wherein preferably the characterization is defined by an average light output degradation over time.

15. The device of any of claims 1 to 14, wherein the supply circuit is adjustable between a plurality of discrete current levels that increase incrementally by a variable current step size that varies according to a non-linear function.

16. The device of claim 15, wherein the non-linear function relates the variable step size to a corresponding brightness emitted by the optical component at each of the plurality of discrete current levels.

17. A method of adjusting light emitted by an optical component over a dynamic range of effective brightness levels, the method comprising: selecting in response to a brightness setting, a pair of two different current levels from among a plurality of discrete current levels, wherein one of the pair of the two different current levels is an intermediate current level that is above zero and below a maximum current associated with a largest brightness level of the dynamic range of effective brightness levels; and modulating between the two different current levels with a modulation duty cycle and at a modulation frequency, wherein the modulation duty cycle and modulation frequency cause lightto be emitted from the optical component with an effective brightness corresponding to the brightness setting, wherein the two current levels are based on a target modulation index for the pair of two different current levels at the modulation frequency.

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