LED based light guide for dual mode aircraft formation lighting

A lighting device (1) includes one or more diode light sources (32), which are configured to emit light into the peripheral edges of a light guide (20). The light guide (20) includes a set of diffusing elements (22) for scattering the emitted light in a plurality of directions out of the front surface of the light guide (20). The diffusing elements (22) are distributed on the light guide (20) so that the scattered light achieves a particular characteristic, e.g., improved uniformity.

FIELD OF THE INVENTION

The present invention is directed to aircraft lighting, and more particularly, to aircraft formation lights utilizing light emitting diodes (LEDs).

BACKGROUND OF THE INVENTION

Formation lights are mounted on the exterior of an aircraft to enhance the aircraft's visibility to other aircraft flying in close proximity. For example, many types of military aircraft utilize formation lights to provide aircraft recognition and spatial orientation during formation flight activities.

Existing aircraft formation lights employ electroluminescent lamp (EL) technology, usually in the form of an electroluminescent strip. However, such conventional formation lights suffer from disadvantages relating to degradation that occurs over time. Generally, the luminescence decreases rapidly, usually decreasing by a factor of 2 within only a few hundred hours of operation. Accordingly, formation lights utilizing EL technology quickly become hard to recognize by other pilots. This results in a potentially dangerous situation when aircraft are flying in close proximity during low visibility conditions, such as nighttime.

The shape and size of formation lights must conform to various requirements. Among these constraints is that the formation lights must be relatively thin. Generally, the thickness of the formation lights used on the exterior of aircraft is less than a ½ inch (1.27 cm).

Thus, it would be advantageous to provide a formation light that exhibits less degradation over time, while maintaining the same package thickness and light uniformity as existing EL technology. Furthermore, a diode light source formation light may be much brighter than traditional EL technology.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention are directed to a lighting device that utilizes a diode light source, while maintaining a package thickness and light uniformity suitable for an aircraft formation light. The device may use, for example, one or more light emitting diodes (LEDs) as light sources.

According to an exemplary embodiment, the lighting device includes a light guide having a set of diffusing elements, and one or more diode light sources configured so as to emit light into one or more peripheral edges of the light guide. The diffusing elements are operable to scatter the light from the diode light sources in such a manner that the scattered light exits a front surface of the light guide in a plurality of directions. In an exemplary embodiment, the light guide is located in front of a reflective base. Thus, light emanating from the diode light sources to the rear surface of the light guide may be reflected into a “visible” direction, i.e., toward the front surface.

The diffusing element may be distributed over a rear surface of the light guide in order to achieve certain visual characteristics. For example, the distribution of diffusing elements may be designed so that the output light is uniformly bright along the lighting device. Also, the diffusing elements may allow the output light to seem uniformly bright when viewed from each of a plurality of directions.

Accordingly, various aspects of the diffusing elements, such as their shape, size and relative spacing, may be designed to achieve the desired visual characteristic. According to an exemplary embodiment, the configuration of the diffusing elements may be designed based on a computer simulation.

In an exemplary embodiment, the light guide may be formed of a transparent plastic material (such as acrylic), and the diffusing elements make comprise etchings on the rear surface of the plastic light guide. For example, the diffusing elements may be laser etched on the rear surface of the light guide.

In an alternative exemplary embodiment, the diffusing elements may be incorporated in an external coating of the rear surface of the light guide, e.g., painted or printed on the rear surface.

In an exemplary embodiment of the present invention, the diode light sources may include light emitting diodes (LEDs) for emitting visible light. In another exemplary embodiment, the diode light sources may include infrared (IR) diodes for emitting infrared light.

According to one exemplary embodiment, the lighting device may be configured as a dual mode device including both LEDs and IR diodes as its diode light sources. In such an embodiment, the lighting device may selectively operate in a visible mode for outputting visible light, and in an infrared mode for outputting infrared light. This dual mode configuration may allow the lighting device to be used as a formation light on military aircraft, which emits aviation green light during normal flight and IR light during covert operations.

The lighting device according to exemplary embodiments may further include a diffuse transmissive layer configured to redirect the light scattered by the diffusing elements of the light guide. The diffused transmissive layer may be designed to improve the visual characteristics (e.g., uniformity) of the light. For example, the diffused transmissive layer may be implemented in an outer lens of the lighting device or as a sheet between the light guide and the outer lens.

In an exemplary embodiment, the lighting device may be implemented, as a formation light on an aircraft. Accordingly, an accumulative thickness of the device, including the light guide, may be less than, or substantially equal to, ½ of an inch (1.27 cm).

Further scope and applicability of the present invention will become apparent from the detailed description provided below. However, it should be understood that the detailed description and specific embodiments therein, while disclosing preferred embodiments of the invention, are provided for purposes of illustration only. Those skilled in the art will appreciate that various changes and modifications are within the spirit and scope of the invention and will become apparent from the detailed description that follows.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention are directed to a lighting device that utilizes a diode light source, and is suitable for use as a formation light on the exterior of an aircraft.

FIG. 1Aillustrates various components in a lighting device according to an exemplary embodiment of the present invention. InFIG. 1A, the lighting device1includes a base10having a reflective layer or surface15. A light guide20is applied over, or in front of, the base10. A series of surface-mounted diode light sources30are located in relation with the light guide20in order to emit light in a direction incident to the peripheral edge of the light guide20. (This may be referred to as “injecting” light into the edges of the light guide20).

Although only one set of surface-mounted diode light sources30are shown, exemplary embodiment of the present invention may include two sets of diode light sources30, each configured to inject light into a length-wise edge of the light guide20. In another exemplary embodiment, additional sets of surface-mounted light diode sources30may be included, so as to inject light into either three or four of the edges of the light guide20. Thus, light may be injected into both length- and width-wise edges of the light guide20.

Referring toFIG. 1A, a diffuse transmissive layer40is placed in front of the front surface of the light guide20. This diffuse transmissive layer40may be configured as a lens or window, which is housed by an opaque housing50. In another embodiment, a diffuse transmissive layer may comprise a sheet placed between the light guide and the outer lens.

It should be noted that the various components of the lighting device1will be described using direction-specific terms including “front” and “rear.” Use of such terms is not meant to limit the lighting device for use in a specific direction. For purposes of description, terms such as “in front of” are used interchangeably with terms such as “above” or “over.” Likewise, terms such as “behind” are used interchangeably with words like “under” or “beneath.” As such, for purposes of description, the base10will be described as being at the “bottom” or “rear” at the lighting device1, while subsequent components are described as being in front of, or over, the base10.

FIG. 1Billustrates an exemplary embodiment where the various components of the lighting device1are assembled and ready for operation. The particular embodiments illustrated inFIGS. 1A and 1Bare particularly suitable for an application where the lighting device1is used as a formation light to be mounted on the exterior of an aircraft.

A more detailed description of the various components illustrated inFIG. 1Ais provided below.

Base10may have a reflective surface or layer15. For example, the base10may be formed of a material whose surface is reflective. Alternatively, the base10may be covered, at least partially, by an external coating15, which exhibits reflective properties.

Thus, light emitted from the set(s) of diode-light sources30toward base10may be reflected into a visible direction (i.e., toward the front of the device1).

Each set of surface-mounted diode light sources30may be comprised of light emitting diodes (LEDs), infrared (IR) diodes, or a combination of both. In an exemplary embodiment, a set of diode light sources30along one of the edges of the light guide20may be comprised of LEDs, while a set of diode light sources30along another edge of the light guide20is comprised of IR diodes. Alternatively, both IR diodes and LEDs may be affixed to a particular set of surface-mounted diodes30.

In an exemplary embodiment where both LEDs and IR diodes are used, the lighting device1may be configured to operate according to dual modes. The lighting device1may be used as an aircraft formation light having both a visible mode and covert mode of operation. Thus, only the LEDs will illuminate in visible mode, and only the IR diodes will be turned on in covert mode. The ability of a formation light to operate in a covert mode may be advantageous for military aircraft during nighttime applications to avoid detection by, e.g., enemy forces.

FIG. 2Aillustrates the configuration of sets of surface-mounted diode light sources30in relation with the base10. InFIG. 2A, each set of diode light sources30is comprised of individual diode light sources32(e.g., LED or IR diodes) that are mounted or affixed to a surface substantially perpendicular to the base10. It should be noted that each set of diode light sources may be also mounted on the base10if side-emitting diode light sources are used. It should be noted that the configuration shown inFIG. 2Amay be modified by including additional sets of diode light sources30at the edges running along the width of device1.

The reflective layer15inFIG. 2Ais operable to reflect light emitted from each diode light source32upward, i.e., toward the diffuse transmissive layer40shown inFIG. 1A. Since the lighting device1is configured to output light in this direction, the reflective layer15provides the advantage of increasing the amount of viewable light emitted by the device1.

It should be noted thatFIG. 2Ais provided for the purpose of illustration, and thus, does not limit the present invention. Various modifications to this configuration may be made without departing from the spirit and scope of the invention. For example, instead of using sets of surface-mounted diode light sources30, it may be possible to configure the diode light sources32to be mounted directly on the base10. For example, side-emitting diodes may be used as light sources32(as described above), or the diode light sources32may be mounted to emit in an upward direction. Alternatively, each diode light source32may be mounted on a separate surface, rather than all diode light sources32being mounted on the same surface along each edge. Furthermore, the shape and dimensions of the base10and sets of surface-mounted diode light sources30may be modified to suit different types of applications, as will be contemplated by those of ordinary skill in the art.

Referring toFIG. 1A, the light guide20is placed in front of the reflective surface15of the base10so that the peripheral edges of the light guide20may receive light emitted from the sets of surface-mounted diode light sources30.FIG. 2Billustrates the placement of the light guide20in relation to each set of diode light sources30and the base10.

According to an exemplary embodiment, the sets of surface-mounted diode light sources30are placed in relation to the light guide20so that each diode light source32emits light in a direction incident to a peripheral edge of the light guide20.

According to an exemplary embodiment, the light guide20may include a set of diffusing elements, or disruptors, on the rear surface (i.e., the surface adjacent to the base10). These diffusing elements are illustrated as elements22inFIG. 3A.

In an exemplary embodiment, the light guide20may be comprised of an acrylic material. In such an embodiment, the diffusing elements22may be laser etched directly to the rear surface of the light guide20. In an alternative embodiment, the diffusing elements22may be applied to an external layer or coding on the rear surface of the light guide20, for example, painted or printed on the rear surface.

According to an exemplary embodiment, the diffusing elements22are distributed over the rear surface of the light guide20according to a pattern or configuration designed to achieve a particular viewable characteristic. In this embodiment, the diffusing elements22are operable to scatter at least a portion of the light emitted by diode light sources32into the light guide20. The particular configuration of the plurality of diffusing elements22, including the size, shape, and relative spacing between diffusing elements22, may dramatically affect the distribution of light emitted out of the lighting device1(through the transmissive diffuse window40and any outer lens). Thus, by altering one or more of these configurable attributes (size, shape, spacing, etc.) in the pattern of diffusing elements22of light guide20, illumination properties of the lighting device1may be improved.

For instance, altering the configuration of diffusing elements22on the rear surface of the light guide20may improve the uniformity of light along the length of the front surface of the light guide20. As a result, the perceived brightness of the light emanating from light guide20(and, thus, output from the lighting device1) may be substantially uniform along the length of the lighting device1.

Furthermore, the configuration of diffusing elements22on the light guide20may be designed to improve the perceived uniformity of brightness when the lighting device1is viewed from different directions. In other words, the diffusing element22may allow the perceived brightness of lighting device1to remain relatively constant as the point of view changes. As such, the brightness will seem about the same when the device1is viewed from an angle as when it is viewed from directly in front.

FIG. 3Aillustrates a particular configuration of diffusing elements22etched on the rear surface of a light guide20. In particular,FIG. 3Ashows an enlarged view of a portion of the light guide20to better illustrate the pattern of diffusing elements22.

The diffusing elements22shown inFIG. 3Acomprise laser etchings on the rear surface of the light guide20. As illustrated, the shape of each diffusing element22is circular, such that the configuration resembles a pattern of dots on the light guide20. As can be readily seen inFIG. 3A, the relative size and spacing of the diffusing elements22need not remain constant along the entire length and width of the light guide20. For example, to improve the visual characteristics of the output light, the size of diffusing elements22, and the relative spacing between diffusing elements22along the edges of the light guide20may differ from the diffusing elements22closer to the center. Also, the shape of the diffusing elements22may change in order to improve visual characteristics.

FIGS. 3B and 3Cillustrate examples of the types of shapes that the diffusing elements22may take.FIGS. 3B and 3Care merely illustrative of the types of available shapes, and do not in any way limit the diffusing elements22to these particular shapes. For example, shapes22A and22F are examples of two-dimensional diffusing elements22that may be painted or printed on the rear surface of the light guide20. On the other hand, shapes22B-22E and22G-22I illustrate examples of three-dimensional shapes that can be etched into the rear surface in order to generate the diffusing elements22.

It should be noted that the various three-dimensional shapes22B-22E and22G-22I illustratedFIGS. 3B and 3Ccontain exaggerated depths in order to more clearly illustrate the types of shapes that can be used. According to an exemplary embodiment, the etched depth of a diffusing element22may be very small relative to the diffusing element's22surface dimensions, such as length, width, radius, etc.

Although the diffusing elements22have been described above as being laser-etched or painted onto the rear surface of the light guide20, it will be readily apparent to those of ordinary skill in the art that other methods may be used to apply the diffusing elements22. For example, the diffusing elements may be chemically etched into the light guide20. Furthermore, although the light guide20has been described as being composed of an acrylic material, other various materials having suitable optical properties may be used, as will be contemplated by those of ordinary skill in the art.

According to an exemplary embodiment, the size, shape, and relative spacing of the diffusing elements22may be determined using a computer simulation. Such computer simulations may take into account factors including the type and thickness of material used for the light guide20, as well as the positioning and properties of diode light sources32. Based on these factors, the simulation may determine certain characteristics of the light emanating from the light guide20as a function of the shape, size, relative spacing, etc. of the diffusing elements22. Such simulations may be implemented by any known combination of computer-based hardware and software, as will be readily apparent to those of ordinary skill in the art.

For example, such computer-based simulation may allow designers to perform trial-and-error on different configurations of diffusing elements22, in order to determine a configuration that provides desired visual characteristics, such as uniformity along the length of the lighting device1and uniformity from different viewing angles.

However, other methods utilizing trial-and-error and/or calculations may be used to determine the configuration of diffusing elements22without the use of computer simulations, as will be readily contemplated by those of ordinary skill in the art.

Referring again toFIG. 1A, a diffuse transmissive layer40may be placed in front of the light guide20in order to further improve the perceived uniformity of the output light, according to an exemplary embodiment. Various types of diffuse transmissive materials, as will be readily apparent to those of ordinary skill in the art, may be implemented as the diffused transmissive layer40.

A function of the diffused transmissive layer40is to ensure that the pattern or configuration of the diffusing elements22of the light guide20is not directly visible when the lighting device1is operational. Accordingly, the design and configuration of the diffuse transmissive layer40may be dependent upon the configuration of the diffusing elements22arranged on the rear surface of the light guide20. Various methods are well known in the art for configuring a diffuse transmissive layer40based on the pattern of diffusing elements22to increase the uniformity of visible light, thereby preventing the pattern of diffusing elements22from being visible.

However, it may not be critical to prevent the pattern of diffusing elements22from being visible at the output of lighting device1. In such applications, the diffused transmissive layer40may be omitted.

According to an exemplary embodiment, the diffuse transmissive layer40may be incorporated into an outer lens, which is secured onto the lighting device1by the opaque housing50. For example, the outer lens may be formed of a diffuse transmissive material. In an alternative embodiment, the diffuse transmissive layer40may be implemented behind a clear outer lens.

According to an exemplary embodiment, the lighting device1may be implemented as an aircraft formation lighting device.FIG. 4Aillustrates various locations100on an aircraft on which the aircraft formation light may be mounted. In such applications, various constraints may be placed on the thickness of the lighting device1, when assembled as shown inFIG. 1B. In a particular exemplary embodiment, the accumulative thickness of the diffused transmissive layer40, light guide20, and reflective base10may be limited. For example, this thickness may be substantially equal to, or less than, ½ of an inch.FIG. 4Billustrates an example of an aircraft formation light1′ constructed according to principles of the present invention and mounted at a location100′ on the aircraft's fuselage.

Furthermore, an aircraft formation lighting device1, in accordance with exemplary embodiments of the present invention, may operate in dual modes—visible and covert. As discussed above, the formation lighting device1may be configured to emit infrared (IR) light in covert mode, so that the formation light is visible only through the use of Night Visual Goggle (NVG) technology. For example, a set of military aircraft flying in formation during a covert operation may utilize formation lighting devices1in covert (IR) mode so as not to be visible to enemy aircraft or ground forces.

It should be noted, however, that the lighting device1is not limited to only two modes. For example, the lighting device1may be configured to operate in either a covert (IR) mode, or one of a plurality of visible modes. In such an embodiment, each visible mode may correspond to a different color illuminated by the lighting device1. For example, if the sets of diode light sources30include red and green light emitting diodes32, the lighting device1may include different modes corresponding to red and green light.