Patent Description:
Aircraft include anti-collision lights, for example, flashing red or white lights, located on an exterior of the aircraft to visually indicate the aircraft is in the vicinity. Each anti-collision light should meet regulatory requirements for light intensity. Current anti-collision lights tend to employ light emitting diodes, which can degrade in performance over time. <CIT> discloses a system for performing an initial power-on self-check for an anti-collision light. A further anti-collision light is also known from <CIT>.

According to a first aspect, there is provided an anti-collision light according to claim <NUM>.

Various preferred embodiments are recited in the dependent claims.

The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the exemplary embodiments of the disclosure, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this disclosure and the teachings herein. Thus, the detailed description herein is presented for purposes of illustration only and not limitation.

Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full, and/or any other possible attachment option.

Throughout the present disclosure, like reference numbers denote like elements. Accordingly, elements with like element numbering may be shown in the figures, but may not be necessarily repeated herein for the sake of clarity.

With reference to <FIG>, an exemplary aircraft anti-collision light (ACL) <NUM> is shown, in accordance with various embodiments. ACL <NUM> may comprise an LED circuit board <NUM> having plurality of LEDs <NUM> (referred to herein as "outer LEDs" <NUM>) located thereon. A reflector <NUM> may be mounted to a surface <NUM> of LED circuit board <NUM>. At least, a portion of reflector <NUM> may be located over outer LEDs <NUM>. Reflector <NUM> is configured to distribute the light emitted from outer LEDs <NUM>. A controller and driver circuit board <NUM> may be operationally coupled to LED circuit board <NUM> such that components of LED circuit board <NUM> are in electrical communication with (i.e., are electrically coupled to) components of controller and driver circuit board <NUM>. A lens <NUM> may be located over LED circuit board <NUM>, reflector <NUM>, and controller and driver circuit board <NUM>. Lens <NUM> may protect the circuity of LED circuit board <NUM> and controller and driver circuit board <NUM>. Lens <NUM>, LED circuit board <NUM>, and/or controller and driver circuit board <NUM> may be mounted to a base <NUM> of ACL <NUM>. Base <NUM> may be mounted to an aircraft structure, for example, to a wing or other exterior aircraft surface.

With reference to <FIG> and <FIG>, additional details of LED circuit board <NUM> and reflector <NUM> are illustrated. In <FIG>, a portion of reflector <NUM> is removed to illustrate components located in an interior of reflector <NUM>. In accordance with various embodiments, outer LEDs <NUM> may be oriented in a ring (i.e., <NUM>°) about an exterior of reflector <NUM>. In various embodiments, reflector <NUM> may include one or more mirror(s) <NUM> configured to redirect the light emitted from outer LEDs <NUM>.

LED circuit board <NUM> is configured to flash outer LEDs <NUM> when ACL <NUM> is powered on. In accordance with various embodiments, LED circuit board <NUM> is further configured to perform an initial power-on self-check to determine if the light intensity of outer LEDs <NUM> meets a predetermined light intensity threshold (e.g., meets or exceeds FAA regulations relating to anti-collision light intensity). In this regard, LED circuit board <NUM> may include an end of life detection system <NUM> (<FIG>).

With reference to <FIG>, in accordance with various embodiments, end of life detection system <NUM> includes a reference LED <NUM> and a trend LED <NUM>. Reference LED <NUM> and trend LED <NUM> are mounted on and supported by LED circuit board <NUM>. Reference LED <NUM> and trend LED <NUM> may be electrically coupled to an electrical circuit that includes outer LEDs <NUM>. Trend LED <NUM> is synchronized with outer LEDs <NUM> such that, while ACL <NUM> is turned on, trend LED <NUM> is configured to be powered on and flash at the same time as outer LEDs <NUM>. Synchronizing trend LED <NUM> with outer LEDs <NUM> allows trend LED <NUM> to degrade or "age" at generally the same rate as outer LEDs <NUM>.

In accordance with various embodiments, LED circuit board <NUM> is configured to power reference LED <NUM> during the initial powering on of outer LEDs <NUM>, and to turn off (i.e., no longer power) reference LED <NUM> after a predetermined number of flashes. In this regard, reference LED <NUM> is powered on for an initial comparison to trend LED <NUM> and is then turned off. Stated differently, reference LED <NUM> is powered on during the initial power-on self-check and turned off after the initial power-on self-check. In various embodiments, LED circuit board <NUM> may be configured to flash reference LED <NUM> a predetermined number of times each time ACL <NUM> is powered on. For example, reference LED <NUM> may flash between one and twenty times, between two and ten times, between three and five times, or any desired number of times each time ACL <NUM> is powered on. In various embodiments, reference LED <NUM> flashes three times each time ACL <NUM> is powered on. After the initial flashes, reference LED <NUM> is bypassed or otherwise turned off, such that reference LED <NUM> does not continue flashing with outer LEDs <NUM>. Powering reference LED <NUM> at the initial startup of ACL <NUM> preserves reference LED <NUM> such that even after thousands of hours of operation of outer LEDs <NUM>, reference LED <NUM> exhibits little to no degradation. In this regard, reference LED <NUM> may be generally representative of the performance (e.g., brightness) of outer LEDs <NUM> at initial production (i.e., prior to degradation from use in ACL <NUM>).

In accordance with various embodiments, end of life detection system <NUM> further includes an optical sensor <NUM> and an optical sensor <NUM>. In various embodiments, each of optical sensor <NUM> and optical sensor <NUM> may comprise an optical sensor integrated circuit. Reference LED <NUM> is operationally coupled to optical sensor <NUM>. Trend LED <NUM> is operationally coupled to optical sensor <NUM>. Optical sensor <NUM> is configured to sense and/or measure an intensity (i.e., brightness) of the light emitted from reference LED <NUM>. Optical sensor <NUM> is configured to sense and/or measure an intensity (i.e., brightness) of the light emitted from trend LED <NUM>.

In accordance with various embodiments, reference LED <NUM> and optical sensor <NUM> are housed inside a cavity <NUM> defined by reflector <NUM>. Trend LED <NUM> and optical sensor <NUM> are housed inside a cavity <NUM> defined by reflector <NUM>. Cavity <NUM> may be identical, or nearly identical, to cavity <NUM> to increase the probability that reference LED <NUM> and trend LED <NUM> encounter the same environmental conditions and/or to prevent or reduce outside factors from affecting the comparison of trend LED <NUM> to reference LED <NUM>.

Reference LED <NUM> may be optically coupled to optical sensor <NUM> through an optical path defined by reflector <NUM> and an optical attenuator <NUM>. Stated differently, light emitted from reference LED <NUM> may travel to optical sensor <NUM> via an optical path defined by reflector <NUM> and optical attenuator <NUM>. In various embodiments, optical attenuator <NUM> may be located between a first wall <NUM> and a second wall <NUM> of reflector <NUM>. First and second walls <NUM>, <NUM> may be located in the interior of reflector <NUM>. First and second walls <NUM>, <NUM> may define, at least, a portion of cavity <NUM>. Optical attenuator <NUM>, first wall <NUM>, and second wall <NUM> may be located between reference LED <NUM> and optical sensor <NUM>. Optical attenuator <NUM>, first wall <NUM>, and second wall <NUM> may be configured to block or prevent light emitted from reference LED <NUM> from reaching optical sensor <NUM>. In various embodiments, optical attenuator <NUM> may translate relative to first and second walls <NUM>, <NUM> and/or relative to surface <NUM> of LED circuit board <NUM>. Translating optical attenuator <NUM> may tune, or otherwise control, the amount of light allowed to reach optical sensor <NUM>. In this regard, a position of optical attenuator <NUM> is selected such that the amount of light reaching optical sensor <NUM> is within a measurable range of optical sensor <NUM> (i.e., the position of optical attenuator <NUM> is selected such that the light emitted from reference LED <NUM> does not saturate optical sensor <NUM>).

Trend LED <NUM> may be optically coupled to optical sensor <NUM> through an optical path defined by reflector <NUM> and an optical attenuator <NUM>. Stated differently, light emitted from trend LED <NUM> may travel to optical sensor <NUM> via an optical path defined by reflector <NUM> and optical attenuator <NUM>. In various embodiments, optical attenuator <NUM> may be located between a third wall <NUM> and a fourth wall <NUM> of reflector <NUM>. Third and fourth walls <NUM>, <NUM> may be located in the interior of reflector <NUM>. Third and fourth walls <NUM>, <NUM> may define, at least, a portion of cavity <NUM>. Optical attenuator <NUM>, third wall <NUM>, and fourth wall <NUM> may be located between trend LED <NUM> and optical sensor <NUM>. Optical attenuator <NUM>, third wall <NUM>, and fourth wall <NUM> may be configured to block or prevent, at least, a portion of the light emitted from trend LED <NUM> from reaching optical sensor <NUM>. In various embodiments, optical attenuator <NUM> may translate relative to third and fourth walls <NUM>, <NUM> and/or relative to surface <NUM> of LED circuit board <NUM>. Translating optical attenuator <NUM> may tune, or otherwise control, the amount of light allowed to reach optical sensor <NUM>. In this regard, a position of optical attenuator <NUM> is selected such that the amount of light reaching optical sensor <NUM> is within a measurable range of optical sensor <NUM> (i.e., such that the light emitted from trend LED <NUM> does not saturate optical sensor <NUM>).

With reference to <FIG>, a cross-section view, taken along the line 2C-2C in <FIG>, of optical attenuator <NUM> extending between third wall <NUM> and fourth wall <NUM> of reflector <NUM> is illustrated. While <FIG> illustrates optical attenuator <NUM> it is contemplated and understood that optical attenuator <NUM>, with momentary reference to <FIG>, is arranged in a similar manner and includes elements and the functionalities as described herein with reference to optical attenuator <NUM>. In accordance with various embodiments, optical attenuator <NUM> may extend from third wall <NUM> to fourth wall <NUM>. In various embodiments, optical attenuator <NUM> may be translated toward and away from surface <NUM> of LED circuit board <NUM>. Translating optical attenuator <NUM> modifies optical path <NUM>. In various embodiments, optical attenuator <NUM> may comprise a set screw. With combined reference to <FIG> and <FIG>, in various embodiments, optical attenuator <NUM> may comprise a set screw. Optical attenuators <NUM>, <NUM> may be in threaded engagement with an anchor portion <NUM> of reflector <NUM>. Anchor portion <NUM> may be configured to couple optical attenuators <NUM>, <NUM> to reflector <NUM>. While optical attenuators <NUM>, <NUM> are described as set screws, it is contemplated and understood that other means of optically attenuating the amount of light reaching optical sensors <NUM>, <NUM> may be employed. For example, optical attenuators <NUM>, <NUM> may comprise shutters configured to pivot relative to surface <NUM>; optical attenuators <NUM>, <NUM> may be located in slots defined by first and second walls <NUM>, <NUM> and third and fourth walls <NUM>, <NUM>, respectively, and be configured to slide toward and away from surface <NUM>. In various embodiments, optical attenuators <NUM>, <NUM> may comprise one or more lenses. In various embodiments, optical attenuation may be achieved by painting one or more portions of first wall <NUM> and/or one or more portions of second wall <NUM> a light absorbing color and by painting one or more portions of third wall <NUM> and/or one or more portions of fourth wall <NUM> a light absorbing color.

The position of optical attenuator <NUM>, third wall <NUM>, and fourth wall <NUM> may match, or mirror, the position of optical attenuator <NUM>, first wall <NUM>, and second wall <NUM>, respectively, such that the optical path between reference LED <NUM> and optical sensor <NUM> is identical, or nearly identical, to the optical path between trend LED <NUM> and optical sensor <NUM>. During assembly, the optical paths for reference LED <NUM> and trend LED <NUM> may be mechanically tuned with optical attenuators <NUM>, <NUM>, respectively. The tuning may compensate for minor variations between reference LED <NUM> and trend LED <NUM> and/or for other manufacturing tolerances.

In accordance with various embodiments, reflector <NUM> is configured to isolate cavities <NUM>, <NUM> from one another and from outer LEDs <NUM>. In this regard, reflector <NUM> is configured to block light from entering or exiting cavity <NUM> and to block light from entering or exiting cavity <NUM>. Isolating cavities <NUM>, <NUM> tends to increase the probability that the output of optical sensors <NUM>, <NUM> accurately reflects the light emitted from reference LED <NUM> and trend LED <NUM>.

In accordance with various embodiments, the signals from optical sensors <NUM>, <NUM> may be output to a comparison circuit (e.g., a comparator or operational-amplifier) configured to compare the intensity (i.e., brightness) of light emitted from trend LED <NUM> to the intensity (i.e., brightness) of the light emitted from reference LED <NUM>. In various embodiments, the comparison circuit may be located on control and driver circuit board <NUM> (in <FIG>). In various embodiments, the comparison circuit may be located on LED circuit board <NUM>. In various embodiments, end of life detection system <NUM> is configured as an analog system. In this regard, end of life detection system <NUM> may be configured to perform the initial power-on self-check using a series of discrete circuits and/or without using software. Stated differently, end of life detection system <NUM> may use a series of discrete circuits to measure the intensity (i.e., brightness) of trend LED <NUM> and reference LED <NUM>, to compare the intensity (i.e., brightness) of reference LED <NUM> to a threshold intensity (threshold brightness), to compare the intensity (i.e., brightness) of trend LED <NUM> to the intensity (i.e., brightness) of reference LED <NUM>, and to provide power to outer LEDs <NUM> and/or cause outer LEDs <NUM> to flash based on the comparisons.

In accordance with various embodiments, end of life detection system <NUM> is configured such that if the comparison circuit outputs a signal corresponding to a satisfactory LED brightness (e.g., a signal indicating the brightness of trend LED <NUM> is greater than or equal to a scaled threshold brightness determined based on the brightness of the reference LED <NUM>), then outer LEDs <NUM> continue to flash. End of life detection system <NUM> is further configured such that if the comparison circuit output a signal indicating the LED brightness requirement has not been met (e.g., a signal indicating the brightness of trend LED <NUM> is less than the scaled threshold brightness), outer LEDs <NUM> are turned off. Outer LEDs <NUM> not flashing, after ACL <NUM> has been turned on, indicates a failure of ACL <NUM>. In this regard, outer LEDs <NUM> not flashing, after ACL <NUM> has been turned on, can alert the pilots, ground crew, or maintenance personnel to the failure, which may trigger a maintenance event.

With reference to <FIG>, additional details of end of life detection system <NUM> are illustrated (schematically). In accordance with various embodiment, the light <NUM> emitted from reference LED <NUM> is sensed, or received, by optical sensor <NUM>. Optical sensor <NUM> outputs signal <NUM> corresponding the detected brightness, or intensity, of the light <NUM> emitted by reference LED <NUM>. The light <NUM> emitted from trend LED <NUM> is sensed, or received, by optical sensor <NUM>. Optical sensor <NUM> outputs signal <NUM> corresponding the detected brightness, or intensity, of the light <NUM> emitted from trend LED <NUM>.

Signal <NUM> from optical sensor <NUM> may be output to a sample and hold circuit <NUM>. In various embodiments, sample and hold circuit <NUM> may also include a clearing circuit configured clear or eliminate the measurements from previous flash cycles, such that with each flash cycle, new or "clean" measurements from optical sensor <NUM> are used. Signal <NUM> from optical sensor <NUM> may be output to a sample and hold circuit <NUM>. In various embodiments, sample and hold circuit <NUM> may also include a clearing circuit configured clear or eliminate the measurements from previous flash cycles, such that with each flash cycle, new or "clean" measurements from optical sensor <NUM> are used.

In accordance with various embodiments, the signal <NUM> output from sample and hold circuit <NUM> and the signal <NUM> output from sample and hold circuit <NUM> are sent to comparison circuit <NUM>. In various embodiments, comparison circuit <NUM> may include an absolute threshold comparison circuit <NUM> and a ratiometric comparison circuit <NUM>. Signal <NUM> from sample and hold circuit <NUM> may be sent to absolute threshold comparison circuit <NUM> and to ratiometric comparison circuit <NUM>. Signal <NUM> from sample and hold circuit <NUM> may be sent to ratiometric comparison circuit <NUM>.

Absolute threshold comparison circuit <NUM> is configured to compare signal <NUM> to a predetermined threshold signal. In this regard, absolute threshold comparison circuit <NUM> may be configured to determine if a brightness of reference LED <NUM> meets a predetermined threshold brightness (referred to herein as a predetermined absolute threshold). A signal <NUM> corresponding to the comparison of signal <NUM> to the predetermined threshold signal is sent to pass fail circuit <NUM>. Pass fail circuit <NUM> is configured to output a signal <NUM> corresponding to a pass if signal <NUM> is greater than or equal to the predetermined threshold signal, and to output a signal <NUM> corresponding to a fail if signal <NUM> is less than the predetermined threshold signal. In this regard, the absolute threshold comparison circuit <NUM> may allow for a determination that reference LED <NUM> is turning on and is exhibiting a desired intensity (i.e., brightness) for the comparison to trend LED <NUM>.

Ratiometric comparison circuit <NUM> is configured to compare signal <NUM> to signal <NUM>. In this regard, ratiometric comparison circuit <NUM> may be configured to determine a brightness, or intensity, of trend LED <NUM> relative to the brightness, or intensity, of reference LED <NUM>. A signal <NUM> corresponding to the comparison of signal <NUM> to and signal <NUM> is sent to pass fail circuit <NUM>. Pass fail circuit <NUM> is configured to output a signal <NUM> indicating a pass if the comparison of signal <NUM> to signal <NUM> is greater than or equal to a predetermined comparison threshold and to output a signal <NUM> indicating a fail if the comparison of signal <NUM> to signal <NUM> is less than the predetermined comparison threshold. For example, pass fail circuit <NUM> may be configured to generate a pass signal if signal <NUM> indicates the intensity (i.e., brightness) of the light emitted from trend LED <NUM> is at least, for example, <NUM>% of the intensity (i.e., brightness) of the light emitted from reference LED <NUM>. Continuing with this example, pass fail circuit <NUM> may be configured to generate a fail signal if signal <NUM> indicates the intensity (i.e., brightness)of the light emitted from trend LED <NUM> is less than <NUM>% of the intensity (i.e., brightness)of the light emitted from reference LED <NUM>.

Pass fail signals <NUM>, <NUM> may be output to a latch circuit <NUM>. Latch circuit <NUM> is configured to output a signal <NUM> corresponding to pass the fail signals <NUM>, <NUM> received from pass fail circuits <NUM>, <NUM>, respectively. Signal <NUM> is configured to cause reference LED <NUM> to be turned off or otherwise disabled, thereby preserving reference LED <NUM>. For example, signal <NUM> may cause the power being provided to trend LED <NUM> and to outer LEDs <NUM> to bypass reference LED <NUM>.

In accordance with various embodiments, signal <NUM> is also output to a flash generator circuit <NUM>. Flash generator circuit <NUM> is configured such that if signal <NUM> indicates that signal <NUM> and signal <NUM> were both pass signals, signal <NUM> causes flash generator circuit <NUM> to continue to output a flash command (or signal) <NUM> to outer LEDs <NUM>. Flash command <NUM> causes outer LEDs <NUM> to flash at a desired interval. Flash command <NUM> also causes trend LED <NUM> to flash at the same interval as outer LEDs <NUM>. If signal <NUM> indicates that either signal <NUM> or signal <NUM> was a fail signal, flash generator circuit <NUM> does not output and/or disables the flash command <NUM>. The lack of flash command <NUM> causes outer LEDs <NUM> and trend LED <NUM> to turn off.

End of life detection system <NUM> being configured to cause outer LEDs <NUM> to flash a predetermined number of times upon an initial powering on of ACL <NUM> and to cause outer LEDs <NUM> to stop flashing in response to detection of a light intensity failure allows ACL <NUM> to indicate to the pilots, ground crew, or maintenance personnel that the ACL <NUM> was turned on and/or that power is being provided to the ACL <NUM>, but that another failure condition exits. This can lead to more targeted maintenance of ACL <NUM> (e.g., replacement of power supply versus replacement of outer LEDs <NUM>). Outer LEDs <NUM> no longer flashing after the initial number flashes may indicate that the intensity (i.e., brightness)of ACL <NUM> has fallen below FAA regulations or that a determination of the outer LED intensity (i.e., brightness) was not made due to reference LED <NUM> failing to emit an acceptable brightness for comparison to trend LED <NUM>. In either case, the stoppage flashing of outer LEDs <NUM> alerts the pilots, ground crew, or maintenance personnel to the failure, which can trigger a maintenance event.

With reference to <FIG>, a method <NUM> for performing an initial power-on self-check for an anti-collision light is illustrated. Method <NUM> may include powering on an ACL (step <NUM>). Method <NUM> may include providing power to a plurality of outer LEDs, a reference LED, and a trend LED of the ACL (step <NUM>). Method <NUM> may further include flashing the outer LEDs, the reference LED, and the trend LED a predetermined number of times (step <NUM>). With combined reference to <FIG> and <FIG>, in accordance with various embodiments, step <NUM> may include power on ACL <NUM>. Step <NUM> may include providing power to outer LEDs <NUM>, reference LED <NUM>, and trend LED <NUM>. Step <NUM> may include flashing outer LEDs <NUM>, reference LED <NUM>, and trend LED <NUM> a predetermined number of times (e.g. three times).

In various embodiments, method <NUM> may include comparing the brightness of the reference LED <NUM> to a predetermined absolute threshold (step <NUM>). In various embodiments, method <NUM> may include comparing a brightness of the trend LED <NUM> to a brightness of the reference LED <NUM> (step <NUM>). In various embodiments, step <NUM> is performed if the brightness of reference LED <NUM> is greater than or equal to the predetermined absolute threshold.

Method <NUM> may further include turning off the reference LED <NUM> and turning on or continuing to flash the outer LEDs <NUM> and the trend LED <NUM> if a comparison of the brightness of trend LED <NUM> to the brightness of reference LED <NUM> is greater than or equal to a predetermined comparison threshold (step 312a). In various embodiments, step 312a may include determining if a signal corresponding to the brightness of trend LED <NUM> is greater than or equal to a scaled threshold brightness determined based on a signal corresponding to the brightness of the reference LED <NUM>. The signal corresponding to the brightness of reference LED <NUM> may be output from a first optical sensor (e.g., optical sensor <NUM>) operationally coupled to reference LED <NUM>. The signal corresponding to the brightness of trend LED <NUM> may be output from a second optical sensor (e.g., optical sensor <NUM>) operationally coupled to trend LED <NUM>.

Method <NUM> may further include turning off the reference LED <NUM>, the outer LEDs <NUM>, and the trend LED <NUM> if either the brightness of reference LED <NUM> is less than the predetermined absolute threshold or the comparison of the brightness of trend LED <NUM> to the brightness of reference LED <NUM> is less than the predetermined comparison threshold (step 310b).

In various embodiments, method <NUM> may include attenuating the light emitted from the reference LED <NUM> to be within a measurable range of the first optical sensor. The attenuating the light emitted from the reference LED <NUM> may include translating a first optical attenuator (e.g., optical attenuator <NUM>), located between the reference LED <NUM> and the first optical sensor, relative to a surface of the LED circuit board <NUM>. In various embodiments, method <NUM> may include attenuating the light emitted from the trend LED <NUM> to be within a measurable range of the second optical sensor. The attenuating the light emitted from the trend LED <NUM> may include translating a second optical attenuator (e.g., optical attenuator <NUM>), located between the trend LED <NUM> and the second optical sensor, relative to the surface of the LED circuit board <NUM>.

Benefits and other advantages have been described herein with regard to specific embodiments. However, the benefits, advantages, and any elements that may cause any benefit or advantage to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosure.

In the detailed description herein, references to "various embodiments", "one embodiment", "an embodiment", "an example embodiment", etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic.

Claim 1:
An anti-collision light (<NUM>) comprising an end of life detection system (<NUM>) comprising:
a reflector (<NUM>); and
a plurality of light emitting diodes (<NUM>) located around an exterior of the reflector;
and characterized by:
a controller and driver circuit board (<NUM>) configured to output a flash command to the plurality of light emitting diodes in response to the anti-collision light being powered on, wherein the plurality of light emitting diodes are configured to flash in response to receiving the flash command from the controller and driver circuit board;
a trend light emitting diode (<NUM>) located in an interior of the reflector, wherein the trend light emitting diode is configured to be powered on and to flash with the plurality of light emitting diodes; and
a reference light emitting diode (<NUM>) located in the interior of the reflector, wherein the reference light emitting diode is configured to be powered on during an initial power-on self-check and to be powered off after completion of the initial power-on self-check.