Combination optics light emitting diode landing light

A light module (1) suitable for use as a landing light for an airplane is disclosed, using an elongated array (2) of light emitting diodes (LEDs) as the light source. Light from the LEDs is directed toward a transparent cover (3). The cover (3) may include a plano-convex lens (4) at its center for nominally collimating the light from the LEDs. The cover (3) may also include a generally featureless peripheral region laterally circumferentially surrounding the lens (4). A faceted reflecting surface (6) having a generally parabolic base curvature (8) may extend circumferentially around a longitudinal axis of the landing light from the LEDs to the cover (3). Light exiting the LEDs at a relatively high angle of exitance reflects off the faceted reflecting surface (6) and transmits through the generally featureless peripheral region of the cover (3).

TECHNICAL FIELD

The present invention relates to a light module using light emitting diodes as the light source, and a combination of reflective and refractive optics to produce the desired light output pattern.

BACKGROUND OF THE INVENTION

Aircraft landing lights are primarily intended to illuminate the runway directly ahead of the aircraft, with a secondary function of making the aircraft visible to other aircraft. For smaller airplanes, there may be a single landing light mounted near a lower portion of the front of the airplane. For larger aircraft, there may be multiple landing lights mounted on or near the underside of the airplane, typically near the front landing gear and the underside of the wings near the fuselage, although other locations may also be used. In general, landing lights should be extremely bright in an area or angular range directly in front of the aircraft (sometimes referred to as the “hot spot”), as well as require as little electrical power as possible, be lightweight and durable, and have relatively long lifetimes.

Historically, most landing lights have used incandescent light sources in the “PAR” bulb configuration, which includes a parabolic aluminized reflector. Light leaving the filament toward the transparent portion of the bulb leaves the bulb, and light that misses the transparent portion of the bulb generally reflects off the parabolic reflector and exits the bulb in a generally collimated beam that is superimposed with the directly-exiting light from the filament. In general, these bulbs tend to produce a single bright “hot spot” directly in front of the airplane, with very little illumination elsewhere.

There have been numerous attempts to use LEDs as the light source for various applications. For instance, LED-based vehicle lights or light systems are disclosed in U.S. Pat. No. 7,686,486 (Tessnow), U.S. Pat. Appln. Pub. 2005/0073849 (Rhoads), U.S. Pat. No. 7,806,562 (Behr), U.S. Pat. Appln. Pub. 2009/0213606 (Coushaine), U.S. Pat. No. 7,896,532 (Hsu), U.S. Pat. No. 7,134,774 (Iwasaki). Example LED spotlights are disclosed in U.S. Pat. No. 6,814,470 (Rizkin) and U.S. Pat. No. 7,758,204 (Klipstein). Example components for LED-based lights include a toroidal lens disclosed in U.S. Pat. Appln. Pub. 2008/0310166 (Chinniah), a light-source multiplication device disclosed in U.S. Pat. No. 4,965,488 (Hihi), and a reflective element formed from portions of multiple ellipsoids disclosed in U.S. Pat. No. 7,753,574 (Meyrenaud). An example module that features a linear array of five LEDs with controlling circuitry, emitting from the center of a 50 mm diameter cylindrical housing, is currently sold under the name “JOULE® JFL2 LED System” by Osram Sylvania Inc. of Danvers, Mass.

There is an ongoing need for further improved LED systems. When compared with conventional incandescent bulb-based systems, the LED systems may be smaller, may have significantly longer lifetimes, may require significantly less electrical power for operation, and may provide additional illumination in visible regions other than the “hot spot” directly in front of the airplane.

SUMMARY OF THE INVENTION

An embodiment is a light module. An LED array is centered around a horizontal longitudinal axis. The LED array emits light in an angular distribution centered around the longitudinal axis. A lens is disposed longitudinally adjacent to the LED array for receiving light emitted by the LED array. The lens has a thickness that is a maximum at the longitudinal axis and decreases monotonically away from the longitudinal axis. A reflecting surface extends generally from the LED array toward the lens. Proximate the LED array, the reflecting surface has a lateral diameter generally equal to a lateral outer diameter of the lens. The reflecting surface has a base curvature that is a paraboloid centered about the longitudinal axis and has a focus disposed at a center of the LED array. The reflecting surface includes a plurality of facets superimposed on the base curvature. The facets reflect light into a distribution proximate the longitudinal axis and includes light that is directed farther away from the longitudinal axis in both lateral directions and downward. The lens is supported by a generally transparent cover. The cover includes a peripheral portion that laterally circumferentially surrounds the lens and has a generally constant thickness throughout. The peripheral portion and the lens are both integral to the cover.

DETAILED DESCRIPTION OF THE INVENTION

In this document, the directional terms “up”, “down”, “top”, “bottom”, “side”, “lateral”, “longitudinal” and the like are used to describe the absolute and relative orientations of particular elements. For these descriptions, it is assumed that the light module is for a landing light mounted on the front of an airplane, with an output beam that is directly generally horizontally in front of the airplane. Although there may be some slight inclinations away from true horizontal during use, for the purposes of this document, it will be assumed that a longitudinal axis of the landing light is denoted as being horizontal. It will be understood that while such descriptions provide orientations that occur in typical use, other orientations are certainly possible. The noted descriptive terms, as used herein, still apply to the landing light, even if the landing light has an orientation other than installed in the front of an airplane, or is uninstalled in its typical orientation. In other applications, the light module described herein may be used for headlights or fog lights for automobiles.

A light module suitable for use as a landing light is disclosed, using an elongated array of light emitting diodes (LEDs) as the light source. Light from the LEDs is directed toward a transparent cover. The cover may include a plano-convex lens at its center for nominally collimating the light from the LEDs. The cover may also include a generally featureless peripheral region laterally circumferentially surrounding the lens. A faceted reflecting surface having a generally parabolic base curvature may extend circumferentially around a longitudinal axis of the landing light from the LEDs to the cover. Light exiting the LEDs at a relatively high angle of exitance reflects off the faceted reflecting surface and transmits through the generally featureless peripheral region of the cover. While most of the light from the LEDs ends up in a hot spot near the longitudinal axis, the facets on the reflecting surface may decollimate and/or redirect a portion of the light away from the hot spot to both lateral sides and to an area below the longitudinal axis, which, for an airplane landing light, may be helpful for maneuvering when the airplane is on the ground.

The above paragraph is merely a generalization of several of the elements and features described in detail below, and should not be construed as limiting in any way.

FIG. 1is an exploded-view drawing of an example light module1.FIG. 2is a horizontal cross-sectional drawing of the light module1ofFIG. 1.FIG. 3is a vertical cross-sectional drawing of the light module1ofFIG. 1. Regarding the terms “horizontal” and “vertical”, it should be noted that in actual use, the light module1may be a landing light be mounted on the front of an airplane and, may emit light generally horizontally to illuminate portions of a runway in front of the airplane. For other applications, the light module1may be a headlight or a fog light mounted on the front of an automobile or other vehicle.

The light source for the light module1is an array2of light emitting diodes, or LEDs. Note that in most cases, the LEDs in the array2may emit light directly into air. In other cases, the LEDs may emit light into small glass or plastic hemispheres that are attached at or near the emission surfaces of the individual LEDs.

In general, the LED array2may be elongated in one dimension, such as with a linear array2of individual LEDs. For instance, the LED array2may include a row of five individual LEDs, arranged in a 1 by 5 pattern. The optics of the light module1generally preserve the elongation of the LED array2, so that a particular aspect ratio of the surface area of the LEDs in the LED array2maps to roughly the same aspect ratio in the angular distribution of the so-called “hot spot” that emerges from the light module1. Mathematically, for a particular x- or y-dimension, the angular distribution in radians roughly equals a linear dimension of the LED divided by a focal length of the collimating optics. From this relationship, it becomes clear that if the LED light source is five times larger in x- than in y-, then the angular distribution of light leaving the light module1may be roughly five times wider in x- than in y-. Alternatively, the LED array2may be square, rather than elongated, or may be clustered around a longitudinal axis9of the light module1.

The LED array2may include so-called “white light” LEDs. Typically, a white light LED includes a light source that emits light in the blue or violet portions of the spectrum, and includes a phosphor that absorbs the blue or violet source light and reemits light over a relatively broad part of the spectrum, typically peaking in the yellow wavelengths. When viewed by the human eye, light from a white light LED does appear to be generally white, although there may be a bluish tint to the light from source-emitted light being mixed with the phosphor-emitted light. The spectral characteristics of white light LEDs may be well-suited for the application of a light module1, and may help produce a generally high contrast between the runway and any lines painted on the runway.

The physical package of the LED array2may vary as needed. In some cases, the LED array2may be centered on a flat face of a generally wafer-shaped cylindrical package, and may emit light with an angular distribution that is centered around a longitudinal axis9of the wafer-shaped cylindrical package. It is understood that other suitable physical packages may be used as well.

As an example, a commercially available LED array2that may be suitable for use in the light module1is currently sold under the name “JOULE® JFL2 LED System” by Osram Sylvania Inc. of Danvers, Mass. The JFL2 includes a linear array2of five LEDs with controlling circuitry, emitting from the center of a 50 mm diameter cylindrical housing. The JFL2 accepts input voltages between 9 and 19 volts, and uses 14 watts of power. There is suitable heat sinking in the JFL2. In particular, the JFL2 has a typical predicted lifetime of about 5000 hours, which is significantly longer than most incandescent-based light modules, which may typically last only 25 hours. At present, a typical JFL2 may have a luminous flux typically around 600 lumens, when installed. In general, as LEDs become more efficient over time, this luminous flux number is expected to rise, such as to 750 lumens, 1000 lumens, or 1250 lumens or more. Note that the JFL2 is merely an example of a suitable LED array2; other suitable LED arrays may be used as well.

Depending on the location and direction of light emitted from the LED array2, the emitted light may arrive in one of three locations: at an incident face of a lens at the center of a transparent cover, at a faceted reflective surface that circumferentially surrounds a portion of the longitudinal axis9, or an annular region between the above two locations.

Note that light that enters the annular region directly from the LED array2generally does not contribute significantly to the useful light output, and may be considered wasted. In general, a choice of component size and location may reduce or eliminate this particular condition. For instance, moving the incident face of the lens closer to the LED array2may reduce this condition, as well as extending the faceted reflecting surface longitudinally away from the LED array2. Because this condition can actively be controlled during the design phase of the light module1, we concentrate below on the remaining two conditions, both of which contribute to the output light distribution: (1) light leaving the LED array2at low angles of exitance (i.e., with a relatively small angular deviation away from a longitudinal axis9of the light module1), passing through the lens at the center of the cover, and leaving the cover being generally collimated, and (2) light leaving the LED array2at high angles of exitance, reflecting off the faceted reflecting surface being nominally collimated, and passing through a peripheral portion of the cover. We first describe the particular optical elements in the light module1, then discuss the two conditions noted above.

The generally transparent cover3may be a molded plastic or glass element that includes a lens4in its central portion (i.e., the portion that surrounds the longitudinal axis9of the light module1), and a peripheral portion5that surrounds the lens4. Materials may include any suitable plastic material, such as polycarbonate, or glass, such as a crown glass like BK7, or a flint glass like SF6. In general, the suitable optical materials typically have a refractive index in the visible portion of the spectrum between about 1.4 and about 1.9. Alternatively, the lens4may be manufactured separately from the cover3, and may be held in place or supported by the cover3. As a further alternative, the lens4may be supported by other mechanical supports that hold in place longitudinally adjacent to the LED array2.

In some cases, the generally transparent cover3may help seal the light module1, and may help protect the LED array2and its associated electronics from the natural elements, such as moisture and contamination. Advantageously, the transparent cover3may physically support the lens4with no additional elements, such as “spider arms” or other filamentary structures that extend radially outward from the lens4.

The lens4may be a positive lens. Such a lens4may have a thickness that is a maximum at the longitudinal axis9and decreases monotonically away from the longitudinal axis9. In general, for a positive lens, the center of the lens is thicker than a lateral edge of the lens.

A preferred shape for the lens4is plano-convex, with the generally flat side facing the LED array2, and the convex side facing away from the LED array2. Such a configuration may be preferred for optical considerations, because for a collimating lens, a plano-convex lens having a light source facing the flat side and a collimated beam emerging from the curved side has reduced coma, when compared to a bi-convex lens or a plano-convex lens in the reverse orientation. Note that coma is a wavefront aberration, and that a reduction in wavefront aberrations for an element generally leads to relaxed tolerances when manufacturing and aligning the element. Such a configuration may also be preferred for manufacturing considerations, because some particular molding processes may be simpler if they include a flat side to the lens, rather than a curved side.

For a plano-convex lens4in air, the focal length is given by the (refractive index minus 1), multiplied by the radius of curvature of the convex side. If the LED array2is placed at the focal plane of the lens4, then light emitted from the LED array2emerges from the lens4as being generally collimated. If the LED array2is centered on the longitudinal axis9of the light module1, the generally collimated light may have a far-field distribution that is generally centered along the longitudinal axis9. Because the LED is elongated along the horizontal axis, the far-field distribution may also be elongated along the horizontal axis.

Note that even though the emergent light may be collimated, the light distribution may have a finite (non-zero) angular spread to it. This occurs as a natural consequence of collimating an extended source. In general, after collimation by an element having a focal length “F”, an extended source having a size “X” will produce a collimated distribution having an angular spread, in radians, given by X/F. The larger the light source, the larger the angular spread. Some typical values for angular spread from the light module1may be full-widths of about 12 degrees in the horizontal direction and about 6 degrees in the vertical direction, measured in simulation at 10% of the peak candela value. It is understood that these numerical values are merely examples, and that other numerical values may also be used.

The plano-convex lens4may include an aspheric component to the convex side. In other words, the curvature of the convex side may deviate from a true spherical surface by a small amount that is described numerically by one or more aspheric coefficients and/or a non-zero conic constant. Such numerical descriptions of aspheric surfaces are well-known in the art. Note that the flat side to the lens4does not produce any inherent wavefront aberrations, and generally does not benefit from adding any aspheric components.

Although the lens4may have a radius of curvature that is symmetric in both the horizontal and vertical directions, the lens4may have aspheric components that are different in the horizontal and vertical directions. Note that such differences are fairly minute, and that an observer will likely not be able to detect such an asymmetry by eye, just by looking at the surface.

In the vertical direction, given by a vertical cross-section of the convex surface, the aspheric component may be used to reduce or eliminate spherical aberration. Note that spherical aberration is a wavefront aberration, and that lenses having excessive amounts of spherical aberration may show reduced performance. Performance of the lens4may be improved by adding the aspheric component in the vertical direction of the convex surface of the lens, which may reduce or eliminate spherical aberration.

In the horizontal direction, given by a horizontal cross-section of the convex surface, very good correction of spherical aberration may lead to an unexpected, and potentially undesirable, feature in the light output from the lens4. Specifically, the LED array2is made up of individual LEDs, typically arranged as squares, and separated by small dead spaces from which no light emerges. If one were to collimate the light from such an LED array2with a very well-corrected lens4, one would see these dead spaces in the angular distribution of the collimated beam. In other words, there would be particular angles, corresponding to the dead spaces between adjacent LEDs, at which the light output distribution would be dark. This would show up as dark stripes on the runway, parallel to the direction of travel, which would be highly undesirable.

In order to avoid having these undesirable dark locations in the output, the aspheric component in the horizontal direction may be set to something other than the value that gives the best spherical aberration correction. Having less-than-optimal spherical aberration correction in the horizontal direction may lead to desirable slight blurring in the horizontal direction. With this slight blurring, the bright areas from the active LEDs are blended over the dark areas between the LEDs to smooth out the light distribution. Note that this blurring may also blur out the sharp lateral edges to the light distribution, which is far less objectionable than having dark lines in the light distribution.

Note that for this particular application, the term “generally collimated” is intended to include both the well-corrected case in the vertical direction, as well as the slight blurring that occurs in the horizontal direction.

Having discussed the lens4in the central portion of the cover3, we turn to the peripheral portion5that surrounds the lens4.

The peripheral portion5may be a generally thin portion of the outside shell of a cone, extending from a lateral edge of the flat side of the plano-convex lens to a lateral edge of the faceted reflecting surface, and if desired, laterally and/or longitudinally beyond the faceted reflecting surface. The cover3may attach to a housing (not shown) at its lateral edge, and therefore the peripheral portion5may physically support the lens4. Note that in some cases, the lens4is made integral with the cover3; in other cases, the lens4may be made separately and attached to the cover3.

In some cases, the only optical function of the peripheral portion5may be to transmit nominally collimated light that has been reflected by the faceted reflecting surface6. For these cases, the peripheral portion5may be essentially featureless, and may have an essentially constant thickness throughout. In other cases, the thickness may vary in a slowly-varying manner, such as a wedge that increases the thickness of the peripheral portion5from one edge to another. In each of these cases, the peripheral portion5receives nominally collimated light and transmits the nominally collimated light without significantly altering its collimation.

Note that there is a design trade-off involved with how far the peripheral portion5should extend longitudinally beyond the flat side of the lens4. In the extreme case where the peripheral portion5extends purely laterally from the flat side of the lens4, there may be a large fraction of the light emitted from the LED array2that passes through peripheral portion5without first reflecting off the faceted reflecting surface6, thereby wasting too large a fraction of the light. In the other extreme, where the peripheral portion5extends a great distance longitudinally beyond the flat side of the lens, there may be a significant fraction of light wasted by Fresnel reflections entering and exiting the peripheral portion5of the cover3, which would occur at unnecessarily high angles of incidence.

In practice, a reasonable compromise may be dictated by the condition at which rays leaving the LED array2and just missing the lateral edge of the flat side of the lens4just strike the longitudinal edge of the faceted reflecting surface6. Optically, there is little reason to extend the faceted reflecting surface6, and the accompanying peripheral portion5of the cover3, longitudinally beyond this condition.

Also in practice, there may be volume constraints on the light module1. For instance, the LED-based light module1may have to fit within the volume envelope that the comparable incandescent-based light once fit. For instance, the light module1may fit into an existing mounting structure for a PAR 36 bulb. It will be understood that these volume constraints may be extended to many other sizes of par lamps and other applications as well.

Having discussed the lens4and peripheral portion5of the cover3, we turn to the faceted reflecting surface6.FIG. 4is a horizontal cross-sectional drawing of the light module ofFIG. 1, analogous toFIG. 2, but showing only a slice of the optical surfaces.

In most cases, the faceted reflecting surface6may be formed as a metallic coating, such as aluminum, deposited on a front surface of a molded plastic or glass element. For these cases, the reflecting surface may be air-incident. In other cases, the reflecting surface may lie beneath a protective layer so that it is not truly air-incident. In still other cases, the reflecting surface may be deposited on the rear surface of the molded element. For all of these configurations, the reflecting surface is the quantity of interest, since the light from the LED array2reflects off this reflecting surface before transmitting through the peripheral portion5of the cover3and exiting the light module1.

Although the faceted reflecting surface6is a tangible structure producing a tangible reflection, it may be easiest to think of the surface itself as being formed from a virtual surface having a base curvature8, with the facets forming relatively small perturbations from the base curvature8. It is instructive to discuss what characteristics reflections from the base curvature8would have, despite there being no physical surface from which to reflect. Once these virtual reflections are understood, one may more easily understand the perturbations to these virtual reflections caused by the facets.

The base curvature8of the faceted reflecting surface6may be a paraboloid centered about the longitudinal axis9and having a focus disposed at a center of the LED array2. Light originating from the center of the LED array2would be collimated by a reflection off the base curvature8, and would be reflected in a direction parallel to the longitudinal axis9. Light originating from locations elsewhere on the LED array2, other than at the center, would also be collimated, but would be reflected in directions that form non-zero angles with respect to the longitudinal axis9. This behavior is analogous to transmission through the lens4, in that the beam, after collimation, includes a range of propagation angles that vary with the size of the LED array2, divided by the focal length of the corresponding collimation element. Note that the respective focal lengths of the paraboloid and the lens may be the same, or may be different.

If there were no facets present, the light reflected off the base curvature8would be collimated, would all pass through the peripheral portion5of the cover3, and would resemble the light that passes through the lens, optionally with different angular extents if the focal lengths of the paraboloid and the lens were different. This would lead to the output distribution having a so-called “hot spot”, with little or no light being present outside the hot spot.

The presence of the facets ensures that some of the light reflecting off the faceted reflecting surface6deliberately ends up outside the hot spot. InFIG. 4, the dashed rays represent light reflected from a virtual surface having the base curvature8, and the solid rays represent light reflecting from the physical facets.

In particular, some or all of the facets provide some tilt and/or decollimation to the reflected beam, when compared with a virtual reflection from the base curvature8. The deviations of the facets from the base curvature8may include a plane of particular orientation, which redirects the beam from the nominal base curvature8reflection, and may include some curvature, which may slightly decollimate the beam from the nominal base curvature8reflection. In some cases, the curvatures of the facets may be different in the horizontal and vertical directions, and may even be of opposite sign. Note that the facets themselves may be curved or may be flat.

In particular, when compared with reflections of light from the LED array2off a virtual surface shaped as a the base curvature8paraboloid, reflections off the facets include light that is directed farther away from the longitudinal axis9in both lateral directions and downward. Such a direction of light away from the “hot spot” may be beneficial in that it may provide additional visibility to the lateral sides of the runway and directly in front of the airplane when the plane is maneuvering on the ground. Note that in general, such deviations away from the hot spot are generally not possible with conventional incandescent-based light modules that use parabolic reflectors.

The actual locations and orientations of the facets may be varied as needed. In some cases, the facets may have borders that are elongated vertically, although they may optionally be elongated horizontally, may be square, or may be a combination of regular and/or irregular elongations. In some cases, there may be two, three, four, five, six, seven, eight, nine, 10, 11, 12, 18, 20 or more than 20 individual facets. In some cases, a single facet may extend vertically across the entire faceted reflective surface; in other cases, the facets may end at a border between a top half and a bottom half of the faceted reflective surface.

FIG. 5is an example two-dimensional contour plot of the light intensity exiting the light module1through the lens. The intensity is the optical power per solid angle, as a function of propagation angle in the horizontal and vertical directions. On the plot, the longitudinal axis9is at the intersection of the zero horizontal propagation angle and the zero vertical propagation angle. The distribution plotted distribution generally corresponds to the “hot spot” that one would see from the cockpit of an airplane, looking out the front window down the runway.

In the example ofFIG. 5, the output light is essentially uniform over a generally rectangular angular range, where the rectangle is wider in the horizontal direction than in the vertical direction. The aspect ratio of the rectangle is roughly the same as the aspect ratio of the LED array2. As noted above, the lens may include a small amount of spherical aberration in one direction, which may smooth out the intensity distribution along the horizontal direction, in order to avoid seeing dark bands in the output that arise from the spaces between adjacent LEDs in the LED array2.

Note thatFIG. 5plots only the light that exits through the lens4at the center of the cover3.FIG. 6is an example two-dimensional contour plot of the light intensity exiting the light module1after reflecting off the faceted reflecting surface6. Note that the absolute scales may be the same or different forFIGS. 5 and 6.

Compared withFIG. 5, the plot ofFIG. 6shows that some light is deliberately directed laterally and downward out of the hot spot. When an airplane is on the ground, this light may help better illuminate the lateral portions of the runway and the area directly in front of the plane. As noted above, most or all of this redirected light arises from facets on the faceted reflecting surface6having a slight departure from the paraboloidal base curvature8of the faceted reflecting surface6.

Note thatFIG. 6plots only the light that exits through the light module1after reflecting off the faceted reflecting surface6. The true output of the light module is the superposition of the intensities shown inFIGS. 5 and 6.

FIG. 7is a flow chart describing the general operation of the light module1. This flow chart is intended to be merely a summary of the operation, and is not intended to be limiting in any way. The LED array2produces an emitted beam, with the center of the beam being directed toward the lens4in the center of the cover3, and the edge of the beam simultaneously being directed toward the reflector.

For the center of the beam, light is generally collimated by the plano-convex lens4in the central portion of the cover3. It is understood that lenses having other shapes may be used as well.

Along a vertical cross-section of the convex surface, the aspheric coefficient may be used to correct for spherical aberration, which may lead to excellent collimation of the light. Along a horizontal cross-section of the convex surface, the aspheric coefficient may be used to horizontally blur the angular distribution, which may hide dark spaces in the light output from the space between the individual LEDs. Note that if the aspheric coefficient were used to correct for spherical aberration in this direction as well, then the well-collimated, well-corrected beam might show these dark spaces, which would be undesirable. As such, the term “generally collimated” is intended to include this horizontal blurring that obscures the dark regions in the output.

Light exits the convex surface of the cover3as being generally collimated. Essentially all of the light in this center of the beam, which is generally collimated by the lens, ends up in the so-called “hot spot” that surrounds the longitudinal axis9. The horizontal blurring that hides the dark spaces may produce some slight blurring of the horizontal edges of the hot spot; this condition is included by the phrase “essentially all” of the light.

For the edge of the beam, light is nominally collimated by the faceted reflecting surface6. The faceted reflecting surface6may have a virtual base curvature8in the shape of a paraboloid. The actual reflecting surface may include facets superimposed on top of the virtual base curvature8. Each facet may include some tilt and/or curvature in the horizontal and/or vertical directions. Light reflecting off the facets may not be truly collimated and parallel to the longitudinal axis9, which would be the case if the faceted reflecting surface6lacked the facets and were just a paraboloid, but may include tilts and/or decollimations caused by the facets. The facets redirect a portion of the light to the lateral sides of the hot spot and beneath the hot spot, in order to provide some short-range illumination when the plane is maneuvering on the ground. Note that this redirected light may typically be a small fraction of the light directed toward the hot spot.

After reflection off the faceted reflecting surface6, the light exits the light module1through the peripheral portion5of the cover3.

Note that thus far, it has been assumed that the cover3and faceted reflecting surface are basically rotationally symmetric about the longitudinal axis9. As an alternative, they may also have an elongated, elliptical, square, rectangular, or other polygonal profile.

For instance,FIG. 8is a front-view drawing of a light module11with a cover13that has a generally rectangular boundary between the central portion14and the peripheral portion15. The rectangular boundary may optionally have rounded corners. Other profiles may also be used as well.

Unless otherwise stated, use of the words “substantial” and “substantially” may be construed to include a precise relationship, condition, arrangement, orientation, and/or other characteristic, and deviations thereof as understood by one of ordinary skill in the art, to the extent that such deviations do not materially affect the disclosed methods and systems.

PARTS LIST

1light module2LED array3cover4lens5peripheral portion of cover6faceted reflecting surface8paraboloidal base curvature of faceted reflecting surface9longitudinal axis11light module13cover14central portion of cover15peripheral portion of cover