Abstract:
A runway lighting fixture of the type normally permanently installed at an aircraft installation such as an airport to provide visible light signals to an aircraft, the fixture having an internal, non-visible light source such as an infrared lamp capable of being activated to provide a non-visible light signal to an aircraft specially equipped to see such non-visible signals. An airport normally having arrays of permanent visibly-lighted fixtures can be equipped for long-term or permanent covert operations capability by installing covert, non-visibly-lighted fixtures in place of visibly-lighted fixtures. In a preferred form the covert fixtures are capable of being both visibly and non-visibly lighted to allow normal appearing non-covert operations at the airport, and unobtrusive covert operations whenever needed.

Description:
FIELD OF THE INVENTION 
   The present invention is in the field of airport runway lighting. 
   BACKGROUND OF THE INVENTION 
   Military and other covert air operations often desire or require non-visible runway lighting markers for nighttime operations. This has been achieved with small, man-portable, battery-operated lights that emit infrared light visible only to pilots or ground personnel wearing special goggles or in specially equipped aircraft. These lights are temporarily deployed on existing airstrips and runways, or are scattered about a likely spot to create a makeshift airway, drop zone or landing zone for a few hours. 
   While useful in the field, these deployable covert lights are less useful for fixed, permanent runway installations such as airports where several hours may be needed to set them up, where it is not desirable for the local civilian air traffic and ground personnel to see the deployed lights (including their setup), and where several hours may be needed to retrieve them. These deployable lights are also not suitable for extended, sophisticated, large-scale air operations where aircraft need to use them for sustained periods of time or spot them many miles away, and where detailed, large-scale, easily-adjusted covert lighting patterns may be needed around the airport. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is an apparatus and method for converting a fixed runway installation&#39;s visible runway light fixtures to include at least some covert-capable fixtures that emit a non-visible light signal, such that normal visible-light-using air traffic remains unaffected by and unaware of the covert capability. Aircraft and ground personnel equipped to see the non-visible light signals can accordingly operate and use the runway installation covertly, with or without the visible lights in operation, and without the need to wait for a temporary and obtrusive deployment of covert lights. 
   By runway installation is meant permanent installations that have an essentially permanently-installed array of visible runway and related light fixtures, such as civilian and military airport runways, aircraft carrier runways and helipads, and fixed drop zones used for training and emergency purposes at military and civilian airports. By runway light fixtures is meant fixtures both on and associated with runways, taxiways, drop zones, helipads and the like, useful in assisting aircraft to spot, approach, drop cargo, land and/or take off. Such fixtures include but are not limited to runway centerline lights, edge lights, threshold lights, taxiway lights, approach angle indicator lights, fixed drop zone marker lights, windspeed indicator bars, and wind direction beacons. 
   In a first aspect of the invention, a runway light fixture is provided with an infrared or similar non-visible light source (for example, non-visible spectrum laser light, non-visible ultraviolet light, or a controllable non-visible thermal source capable of being viewed with a passive infrared viewer) capable of being seen only by specially equipped aircraft and personnel. In a preferred form, a visible light fixture of known, ordinary-looking type is modified by replacing a visible light source inside the fixture with a non-visible light source, or replacing the fixture with the same or a similar fixture having both visible and non-visible light sources, such that the visible and non-visible light sources can be operated simultaneously or independently, depending on the lighting needs of the air traffic. 
   In a second aspect of the invention, some or all of the fixtures at an installation can be replaced or modified, as needed. The modified or replaced fixtures can preferably operate on the normal lighting control and power system already in place at the airport, such that maintenance personnel, air control personnel, or even the crew of an approaching aircraft can enable non-visible, covert operations with a direct or remote signal. Alternately, covert-capable fixtures can be made to have their non-visible lights activated individually and/or to use different power sources. 
   Although it is preferred to provide fixtures each capable of both visible and non-visible lighting, it is also possible to switch or complement one or more visible light fixtures with a corresponding number of non-visible-only light fixtures at the landing installation, such that some of the runway fixtures are purely visible fixtures and some are purely covert fixtures capable of providing non-visible light signals to an aircraft. And although most installations will be retrofits or replacements of existing visible lighting fixtures, new runway construction can be originally provided with covert dual- and/or single-mode fixtures. 
   These and other features and advantages of the invention will become apparent upon further reading of the specification, in light of the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic plan view of an exemplary visible lighting arrangement for an airport runway. 
       FIG. 2  is a perspective view of an approach end of the runway of  FIG. 1 , showing in more detail some commonly-used types and placements of runway light fixtures. 
       FIG. 3  is similar to  FIG. 2 , but with several of the visible runway light fixtures being replaced with dual-mode, infrared-capable fixtures of the same type. 
       FIG. 4  is a top plan view of a common type of dual-lamp visible light fixture used to light runway edges, wherein one of the normal visible-light lamp assemblies has been replaced with an infrared lamp assembly, and with an optional set of rear-pointing lamps shown in phantom. 
       FIG. 4A  is a front perspective view of the fixture of  FIG. 4 . 
       FIG. 4B  is a partially sectioned side elevation view of the fixture of  FIG. 4 , showing the side-by-side visible and infrared lamp assemblies and an exemplary wiring and power arrangement. 
       FIG. 4C  is an exploded assembly view of the fixture of  FIG. 4 , with the lamp-containing fixture removed from a common type of ground-embedded base and with an optional power supply illustrated in the base in phantom. 
       FIG. 5  is a top plan view of a dual-direction light of a type often used to light runway centerlines, with a single visible lamp pointing to the front and modified according to the invention with a single non-visible lamp pointing to the rear. 
       FIG. 6  is a plan view of the runway installation of  FIG. 1 , with a number of the runway light fixtures modified or replaced according to the invention and operating in covert mode by emitting non-visible light, as indicated by broken lines. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring first to  FIGS. 1 and 2 , a runway installation  10  is schematically illustrated, with a permanent paved runway  12  of known type at a commercial or military airport. Such runways may or may not have a control tower  18  nearby, depending on the size, type, and activity level of the airport. Runway  12  will, however, have an essentially permanent array of light fixtures on and around the runway and any associated taxiway and terminal structures. For simplicity only a runway  12  is shown, but it will be apparent to those skilled in the art that taxiways, terminals, and other known complementary structures requiring lighting to guide aircraft can be included in runway installation  10 . 
   Runway  12  is typically provided with several different types of light fixture, set in different arrays for different purposes. In the illustrated example, the runway centerline  12   a  is marked at intervals with runway centerline lights  20  of known type, embedded flush or nearly so with the paved surface of the runway and emitting light patterns  21  aligned with the centerline in known fashion. Centerline lights  20  can vary in their construction, are available from many commercial sources, and may be unidirectional for single-direction runways or (as illustrated in  FIG. 1 ) bi-directional for runway operation in both directions or to indicate right and wrong landing direction, for example by emitting light of different color in each direction. 
   The side edges  12   b  of the runway are marked along their length in conventional fashion with runway edge lights  22  of known type, similar to centerline lights  20  but often having two diverging or differently-angled lamps, one throwing a light pattern  23   a  essentially parallel to or only slightly angled in toward the runway edge, and one throwing a more strongly angled or “toed-in” light pattern  23   b  toward the runway centerline. Runway edge lights  22  are often mounted low or nearly flush to the ground like centerline lights  20 , and may be very similar in appearance and function, such that it is known to use the same type of light fixture both for centerline and edge lighting. Runway edge lights  22 , however, often have a deeper mounting base or anchor (not shown, see  FIGS. 3 and 4C ) in the form of a metal cylinder (commonly referred to as a “can”) anchored deeply into the ground or pavement and capable of removably receiving the fixture housing the lamp and lens assemblies. Runway edge lights  22  may also be rotatably adjustable on their mounts, to vary the toe-in angle relative to the runway. 
   The approach end  12   c  of runway  12  is often marked by a geometric pattern of approach lights  24 , for example in a triangle or arrowhead pattern similar to that shown in  FIG. 1 . In the illustrated embodiment of  FIG. 1 , approach lights are similar to runway edge lights  22  in their structure and their low-to-the-ground or inset mounting, but may for example have only a single unidirectional lamp emitting a light pattern  25  pointing generally in the direction of the approaching aircraft. 
   The actual threshold  12   c  of the paved runway  12  is often separately lit, for example by a straight row of vertical post-mounted type threshold lights  26  of known type, often with a multi-directional light pattern to both light the edge of the pavement ( 27   a ) and to be seen by an approaching aircraft ( 27   b ) to clearly mark the transition from approach lights  24  to the actual pavement threshold. 
   The end  12   d  of the runway, where the pavement runs out, will typically be marked with its own array of runway end indicator lights  28 , which again may be post-mounted lights similar to threshold lights  26 . 
   An aircraft&#39;s angle of approach may also be assisted with precision approach path indicator or “PAPI” lights  30 , usually raised, multi-lamp, sometimes multi-color fixtures with the respective angles of the lamps themselves set such that an over/under or on/off color or light pattern  31  discernible to the approaching aircraft can be gauged for a go or no-go landing decision (for example, red-over-white OK to land, white-over-red go around again). 
     FIGS. 1 and 2  also show a windspeed indicator bar  32  of known type, with a vertical array of lamps  33  in mph or kph increments, for example each lit bulb denoting a 10-mph increase in windspeed. A wind-sock or -cone  34  indicates wind direction in known manner, and may be lit at night by a downwardly-angled light or lights set at the top of its pole, again in known manner. 
   It will be apparent to those skilled in the art of runway lighting that many variations on runway lighting patterns exist, that different types of fixture are often mixed and matched in custom arrays, that fixtures intended for one purpose (centerline lighting) may find use at a particular runway installation for a different purpose, and that other known types of runway light fixtures that have not been specifically named above are similar or equivalent to those shown herein for purpose of illustration. 
   Still referring to  FIGS. 1 and 2 , the runway light fixtures are typically powered through underground electrical conduit of known type (not shown), and often controlled at a centralized control panel or station such as a “vault” or building  40  by manual or automated switching and other controls. An operator  50  or pre-programmed control at the vault can turn individual lights and/or arrays on and off; change lighting patterns and direction; and may even be capable of selectively enabling different lamps in one or more fixtures. Such power supply and control structures and methods are well known to those skilled in the art. Control may also be from the tower  18  or even remotely, as from a radio signal transmitted from an approaching aircraft  60  in known manner to enable an automated activation of the runway lights at an unmanned airport. 
   Referring next to  FIG. 3 , installation  10  and runway  12  are shown modified according to the invention with covert-capable light fixtures, essentially identical in outward appearance to the normal visible light fixtures, but capable of emitting a non-visible light pattern instead of, or preferably in addition to, the normal visible light. In the illustrated embodiment of  FIG. 3 , non-visible (e.g., infrared) light patterns are illustrated in broken lines, while visible light emissions are illustrated in solid lines as in  FIGS. 1 and 2 . In the example of  FIG. 3 , centerline lights  20  have been modified or replaced with similar or identical fixtures  120  which are capable of emitting a visible light pattern  121   a  from the approach side and an infrared pattern  121   b  from the opposite side. Centerline fixtures  120  may be fixtures  20  in which a visible lamp assembly or light source has been removed and replaced with an infrared lamp assembly or light source, or may be originally built containing both visible and non-visible lamps. It will be understood that fixtures  120  could be modified or built to emit non-visible light in both directions, either for a dedicated covert runway or alternated with visible-only fixtures along the centerline, although the illustrated dual-use fixture is preferred. 
   In  FIG. 3 , runway edge lights  22  from  FIGS. 1 and 2  have been modified or replaced with dual-mode fixtures  122 , in the illustrated embodiment with the outer visible lamp assembly replaced with a non-visible lamp assembly. Fixtures  122  accordingly emit visible light  122   b  onto runway  12 , and non-visible light  122   a  such as infrared along the runway side edges  12   b . The toe-in angle of the non-visible light pattern  122   a  can usually be set to overlap the actual edge of the runway. 
   Likewise in  FIG. 3 , approach lights  24  have been replaced or modified with dual-mode fixtures  124  having both visible and non-visible light emissions  124   a  and  124   b . Elevated threshold lights  26  have been replaced or modified with similar-looking fixtures  126 , also with both visible and non-visible light signals  126   a  and  126   b . Windspeed bar  32  can be modified or replaced with a bar  132  having a plurality of non-visible light sources  133  capable of displaying the same windspeed indications in conjunction with or instead of the normal visible light indications. Wind-cone  34 , or at least its cone-illuminating lights, can be modified or replaced with a non-visible cone-illuminating light or lights to illuminate the cone for air- and ground-crews using proper viewing equipment. 
   Some of the advantages of the invention include the ability to convert an airport to covert runway lighting capability that can be activated, adjusted, and deactivated as quickly and conveniently as the normal visible runway lighting; that is unobtrusive to normal air and ground personnel during the daytime, and which can function in an essentially normal visible mode at night, when desired; that has sufficient power for extended covert use and for the non-visible lighting to be seen from long distances; and that has sufficiently detailed non-visible lighting around the runway to function as an essentially normal runway for night-vision-equipped pilots and ground crews. 
   It will further be appreciated that modification or replacement of existing visible-light-only fixtures can be accomplished quickly and without attracting attention, appearing, for example, as routine maintenance typical with runway lighting fixtures. This may be especially important in sensitive areas or countries, where it is not desirable for locals to know about the runway&#39;s covert capabilities. And a runway or installation so equipped can be quickly denied to or hidden from an enemy by turning off the visible lights in known manner while enabling just the non-visible lights. 
   FIGS.  4  and  4 A– 4 C illustrate one of the edge runway lighting fixtures  122  from  FIG. 3 . In the illustrated embodiment the fixture  122  is a dual-lamp, dual-lens inset type fixture whose housing is of generally known type, but which is modified internally as to its lighting ability according to the invention. Fixture  122  has a strong, durable cover  224 , for example made from cast steel or aluminum, bolted to a bottom cover or with an integrated bottom cover ( FIG. 4A ) to contain and support wiring, lamps, lenses, and other internal components in known manner. Fixture  122  is typically then bolted or screwed with bolts  228  to a cylindrical base. Cover  224  preferably has a rounded or beveled upper surface  230  extending only slightly above ground or pavement level and capable of withstanding aircraft wheels and runway snowplows. Side-by-side windows or lenses  232  transmit light from light sources such as incandescent/quartz and infrared lamps  240  and  242  (hidden lines) mounted inside the fixture. In the illustrated embodiment each window  232  transmits light from a separate lamp assembly. The windows are usually sealed against the elements. Light-directing channels  234  are recessed into the surface of cover  224  to help channel and define the light from each of windows  232 . A rib  236  separates the channels to help maintain the distinct light beam from each window, and also serves to deflect wheels and plow blades away from the windows. 
   In the illustrated embodiment, fixture  122  is illustrated as having a pair of essentially unidirectional windows to make it a one-way fixture, but it is known to provide such fixtures with opposite-facing windows (and associated lights or lamps) as shown in phantom for two-way use. 
     FIG. 4A  illustrates the light sources behind windows  232 , in the illustrated embodiment a standard incandescent or quartz lamp  240  behind one window and an infrared lamp assembly  242  behind the other window. Infrared lamp assembly  242  in the illustrated embodiment is an array of LED (light emitting diode) “bulbs”  242   a  mounted on a PC board  242   b  and emitting infrared light. Infrared LED bulbs and suitable circuitry and boards for powering and controlling them with both alternating and direct current are generally known and commercially available, and can be combined, modified, and arranged in many different ways to be powered by the conventional wiring and power connections already in a runway lighting fixture such as  122  to shine infrared light through a window or lens. Other non-visible light sources or lamps could be used in similar fashion, for example laser light sources. 
     FIG. 4B  shows fixture  122  in section, with a standard incandescent lamp  240  having a bulb/reflector assembly  240   a  connected by wiring  240   b  to electrical power supply terminals  250  in known fashion. Terminals  250  are supplied with electrical power from an external source through wire connection to an external power conduit  272 , for example with a sealed connector plug  270  attached to bottom cover  226  and making a sealed electrical connection through the cover to terminals  250 . Power conduit  272  brings electrical power, usually high voltage (240V or 120V) alternating current, from a centralized source or substation such as the control vault in serial or parallel fashion to one or more runway lighting fixtures. 
   The non-visible (infrared) lamp assembly  242  in fixture  222  is connected through its PC board  242   b  by wiring  242   c  to power terminals  250 , to use the same electrical power supplied to the incandescent/quartz lamp assembly. It may be desirable for the infrared assembly  242  to use the same power supply from terminals  250 , but a different voltage or even a different type of current (for example, direct current) to light the LED bulbs. For this purpose a transformer or converter of known type (not shown) can be connected between board  242   b  and terminals  250  in known fashion. It may be desirable for the infrared lamp assembly  242  to have its own independent power supply, for example a separate external conduit or a manually or remotely activated internal battery in the fixture as primary or backup power, but piggybacking the infrared assembly to the same power supply used by the standard incandescent lamp assembly and fixture is preferred. 
     FIG. 4C  illustrates an optional mounting arrangement for fixture  122 , in which the fixture is mounted to a deep cylindrical “can” or base  280  of known type, usually made from steel or aluminum and set into the ground or runway pavement in a concrete footing  281 . Base  280  is essentially a sealed, hollow cylinder, with an upper opening  280   a  and a rim or flange  280   b  designed to receive and support fixture  122 . The fixture  122  is removably secured to base  280  with bolts or screws  282 , such that the fixture can be detached for maintenance or repairs. Bases such as  280  provide a convenient support and junction for electrical power, and typically will have one or more openings or hubs for admitting a power cable or conduit in sealed fashion to be connected inside the can, by connector plug or otherwise, to the lamp assemblies in fixture  122 . In the illustrated embodiment, base  280  contains one or more power regulating or supply options such as a self-contained battery  290  and/or a voltage transformer or converter  292  connected to the infrared lamp assembly in fixture  122  with suitable wire or plug connections. 
     FIG. 4C  also illustrates some optional external features of fixture  122  itself. Because the invention is especially useful for unobtrusively replacing conventional visible light fixtures around a runway, a fold-away carry handle  300  is preferably built into the top cover  224  of the fixture to facilitate transport, installation, and removal of the fixture from its base  280  or other mounting location. In some circumstances it may be desirable to replace a standard visible-light fixture with a covert-capable fixture such as  122  having its own independently operated internal power supply and/or control features. Such control features can include turning the infrared lamp on and off independently of the visible lamp assembly, or adjusting the infrared lamp&#39;s operation from a steady burn to a flashing mode, or changing from one flashing mode to another, or function testing. External manual control switches  294 ,  296  can accordingly be placed unobtrusively on the exterior of the top cover  224  to be accessed by knowledgeable ground personnel for operation or adjustment of the infrared lamp assembly. 
     FIG. 5  illustrates an alternate type of fixture embodying the invention, such as one of the two-way centerline fixtures  120  from  FIG. 3 . Fixture  120  has two window/lens assemblies  332  pointing in opposite directions. A visible lamp assembly  340  is located behind one window  332  on one side and an infrared lamp assembly  342  behind the other window on the opposite side. It will be understood that fixture  120  is just one additional example of a known type of runway lighting fixture modified with an internal infrared or other non-visible light source. Virtually any runway lighting fixture with one or more visible lamp assemblies can be modified by replacing a visible lamp with a non-visible lamp or light source, or by adding a non-visible light source to complement a visible lamp assembly; or, can be originally manufactured with both non-visible and visible lamp assemblies. 
   Although the foregoing embodiments show separate windows or lenses for each lamp assembly, it is also possible to place both a visible and an infrared lamp assembly in a runway lighting fixture to shine through a common lens or window. Operation can then be one at a time, or in some cases simultaneously, where, for example, a different signal or intensity or pattern of infrared light would be visible to an infrared-equipped covert pilot while the normal visible signal remained available to normal pilots. 
     FIG. 6  illustrates an alternative example of the invention, in which some but not all of the runway lighting fixtures at the runway installation  10  of  FIG. 1  have been modified or replaced with covert-capable lighting fixtures. In  FIG. 6  approximately every other fixture among the centerline and edge arrays  20 ,  22  is a covert-only fixture  420 ,  422  similar to fixtures  120 ,  122  in  FIG. 3 , but each with two non-visible lamps to emit only infrared or other non-visible light patterns or signals as illustrated in broken lines. It will be understood that the use of staggered or otherwise intermixed covert fixtures could also be achieved with dual-mode fixtures as shown in  FIG. 3 . 
   The foregoing examples of the invention are preferred and alternate embodiments for purpose of explanation. It will be understood by those skilled in the art that the invention can be implemented in ways other than these specific examples without departing from the scope of the invention as defined by the following claims, now that we have disclosed the invention with these examples.