Methods of ImplementingNVIS Compatible Cockpit Lighting

John J. MartinRaytheon Systems Company

Supporting Air Force Research LaboratoryWarfighter Training Research Division

6030 S. Kent, Bldg. 560Mesa,~ 85212-6061

Abstract Introduction and Background

On average, halfofa 24 hour dayis darkness. Military flight operationsdo not stop during hours of darkness,and use of night vision goggles tofacilitate such operations is widespread.For best visual acuity of the intensifiedoutside scene, aircraft cockpit lightingmust be compatible with (not be sensedor intensified by) a night vision imagingsystem (NVIS). Multiple methods ofimplementing NVIS compatible cockpitlighting exist and, with two exceptions,the methods are designed for permanentinstallation. Because aircraft programmanagers are faced with many choiceswhen implementing NVIS compatiblecockpit lighting systems, descriptions ofeach of the lighting methods areprovided to help assist in selection oftheoptimal systemfor a given aircraft.

Concern about the quality ofillumination provided by temporarychemical light sticks has resulted in therecent development of a new NVIScompatible illumination system based onlight emitting diodes (LEDs). The LEDsystem is inexpensive and is intendedfortemporary applications. The system hasprovedpopular, and its design and effecton existing cockpit lighting designparadigms is discussed.

When used in an aircraft cockpit,the primary function of night visiongoggles (NVGs) is to provide intensifiedimagery of distant objects in the outside .environment. NVGs are very sensitiveto light, and it is undesirable for an NVGto sense and intensify light from anysources other than those in the outsideworld. Cockpit instruments and displaysmust remain readable at night by theunaided eye, but any cockpit lightingthat is sensed and intensified by theNVG may cause circuitry in the NVG toautomatically decrease the intensifiergain, degrading the NVG-aided visualacuity (VA) of the outside scene. Oneincompatible cockpit light source ismore than sufficient to degrade NVG­aided VA. The object then is to tailorthe spectral emission of all cockpit lightsources such that they are easily read bythe unaided eye but invisible to theNVG; and similarly, to tailor thespectral response of the NVG so itresponds to light from the outside worldbut is insensitive to light from cockpitsources. Cockpit lighting that is notsensed and intensified by (and thus doesnot interfere with) night vision gogglesis termed Night Vision Imaging System(NVIS) compatible. Such lightingtypically is green, with no red and near-

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1. REPORT DATE MAR 2000 2. REPORT TYPE

3. DATES COVERED

4. TITLE AND SUBTITLE Methods of implementing NVIS compatible cockpit lighting

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6. AUTHOR(S) John Martin

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7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Raytheon Systems Company, ,6030 South Kent Street,Mesa,AZ,85212-6061

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14. ABSTRACT On average, half of a 24-hour day is darkness. Military flight operations do not stop during hours ofdarkness, and use of night vision goggles to facilitate such operations is widespread. For best visual acuityof the intensified outside scene, aircraft cockpit lighting must be compatible with (not to be sensed orintensified) a night vision imaging system (NVIS). Multiple methods of implementing NVIS compatiblecockpit lighting exist and, with two exceptions, the methods are designed for permanent installation.Because aircraft program managers are faced with many choices when implementing NVIS compatiblecockpit lighting systems, descriptions of each of the lighting methods are provided to help assist in selectionof the optimal system for a given aircraft. Concern about the quality of illumination provided bytemporary chemical light sticks has resulted in the recent development of a new NVIS compatibleillumination system based on light emitting diodes (LEDs). The LED system is inexpensive and is intendedfor temporary applications. The system has proved popular, and its design and effect on existing cockpitlighting design paradigms is discussed.

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infrared (IR) spectral components. Tocomplement such lighting, filters areinstalled in the NVG that allow it torespond only to red and near-IR light,thus rendering it blind to the cockpitlighting. Multiple methods exist forimplementing NVIS compatible cockpitlighting. Brief descriptions of themethods follow.

Lighting Methods

Integral illumination

Most if not all existing cockpitinstruments contain integral (internal)lamps to illuminate the given display asneeded. Most existing lamps areincandescent and, along with visiblelight, they emit large amounts of near-IRenergy that is invisible to the unaidedeye. The near-IR energy will be sensedby and may interfere with NVGs in thecockpit, so emission of the near-IRenergy must be prevented.

NVIS compatible integralillumination is implemented by theinstallation of special filters around theexisting internal lamps, or by installationof non-IR-emitting light sources insidethe instrument case. With eitherapproach the internal sources emit no redor near-IR energy, and the illuminateddisplay, although easily read by theunaided eye, appears invisible to NVGs.Integral lighting is durable, requires noaircraft wiring changes, and usuallyprovides very good display readabilitybecause the integral light sources arelocated in those positions determined asoptimal for uniformity of illumination bythe instrument designer. Integrallighting is installed either when theinstrument is manufactured, or as a

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retrofit when the instrument isdisassembled at a qualified repairfacility.

In addition to the instruments, allwarning, caution, and advisoryindicators also must be NVIScompatible. Such indicators usuallyconsist of an alphanumeric legendbehind a window, back-illuminated byone or more lamps. NVIS compatibilitytypically is achieved by replacing theconventional legend/window with a newlegend/window incorporating a specialglass or plastic filter. The special filterblocks the transmission of red and near­IR, but passes other chosen wavelengths.Alternatively, some recently availableindicators contain light sources (Le.,LEDs) that are intrinsically NVIScompatible.

The integral illuminationapproach has a relatively long historyand has proved to be satisfactory interms of compatibility and displayreadability; it is well suited for 'newstart' aircraft and/or cockpit programs.Although the integral illuminationapproach requires no changes to aircraftwiring, it can be costly if not designedinto an instrument from the beginning.Unless externally marked, an integrallylit NVIS compatible instrument usuallyis not apparent as such (especially whenit is unpowered). All similar instrumentsin the entire supply chain must alsocontain the same type of lighting, or elsea flying unit runs the risk of receiving anon-NVIS compatible replacement whenexchanging instruments for repair. Oneincompatible instrument can besufficient to render NVGs ineffective ina cockpit. Instrument configuration andlogistics controls therefore areimportant.

Post and Bezel

Post and bezel illuminationconsists of small light sources (typicallysmall incandescent lamps) in short post­like towers external and adjacent to theinstruments, or in ring-like bezels placedover the instrument faces. Light fromthe sources is directed at the faces of theinstruments, functionally flood-lightingthem from very close range. NVIScompatibility is achieved by integratingspecial filters or sources in the posts andbezels such that red and near-IRwavelengths are not emitted. Locationof posts is important, both in preventingreflected glare on the glass instrumentfaces and in uniformity of illumination.Bezels are mounted directly over theinstrument faces, and the light ''throwdistance" is very short, so bezel designalso is critically important for uniformityof illumination. Bezels often incorporatespecial glass windows that "trap" anddistribute the light across the face of theinstrument as uniformly as possible.

As with integral lighting, thecockpit warning, caution, and advisoryindicators must be NVIS compatible.The same approach used for suchindicators in an integral lightinginstallation typically is used in post andbezel installations.

Power must be supplied to thelamps in the posts and/or bezels, soinstallation of a post and bezel systeminvolves modification of aircraft wiringand passage of wires through theinstrument panel. In some installationsone of the (typically four) screwsmounting an instrument is removed andthe wires are passed through its opening,the remaining screws being sufficient tosecure the instrument in place. In other

3

installations new holes for mountingposts or passing wires may be drilled.Existing lighting circuit wires typicallyare removed at each instrumentconnector, disabling the integralillumination sources in the instruments.Because the integral sources in thecockpit instruments are not used,configuration control of instrumentshaving different internal illuminationsystems is not an issue. However, ifpostand bezel electrical loads- differ from theoriginal lighting system electrical loads,adjustment of aircraft lighting circuitrymay be required to maintain uniformillumination across the cockpit.

With due design considerationgiven to lighting balance and eliminationof reflected glare, a post and bezelsystem can provide satisfactory lighting.The cost of a post and bezel installationusually is substantially less than that ofNVIS compatible integral lighting.

Floodlighting using Existing Fixtures

In addition to the integrallighting installed in instruments, mostaircraft also have a floodlighting(secondary) system to illuminate thecockpit if the instrument primarylighting system fails. The floodlightstypically contain incandescent lamps, arecapable of high luminous intensity, andare located in appropriate positionsaround the cockpit to illuminate allcritical areas. The apertures offloodlights can be fitted with filters thatblock the transmission of red and near­IR light, thus rendering them NVIScompatible. The filters usually must bemade of glass to withstand the heatgenerated by the incandescent lamps inthe enclosed fixtures.

As with integral lighting, thecockpit warning, caution, and advisoryindicators must be NVIS compatible.The same approach used for suchindicators in integral lightinginstallations normally is used infloodlighting installations.

NVIS compatible floodlightingtypically utilizes existing fixtures, andno change to aircraft wiring is required.Existing integral lighting in theinstruments is turned off but is unalteredand usually remains connected, soincompatible integral lighting may beused as a reserve system (withoutNVGs) if floodlighting fails. Floodlightsusually are located at intervals, and thoseinstruments or displays closest to a givenfloodlight will receive greaterillumination than others. Interveningobjects also may cause shadowing ofsome controls or displays. However,floodlighting is relatively inexpensiveand can be an effective means ofimplementing NVIS compatible lighting.

Floodlighting using LED Projectors

In some applications NVIScompatible integral instrument lighting,post and bezel lighting, and floodlightingusing modified existing fixtures may beundesirable. In such situations, floodillumination of controls and displaysmay be provided by a system of modularlight sources ('projectors') mounted inselected locations in the cockpit. Eachmodule consists of a small metalenclosure containing a light emittingdiode (LED) and optics, and projectsuniform NVIS compatible illuminationacross a localized area. Modulesgenerally are identical and are positionedabove the surface area being illuminated.

4

All modules are held in proper positionwith brackets that in turn are mountedusing existing screw locations in thecockpit. The modules are interconnectedwith dedicated wiring that is separatefrom existing aircraft lighting systemwiring. Such wiring is routed in anunobtrusive and noninvasive manner,and is clamped or otherwise secured inplace to prevent movement and snaggingwherever the wiring is exposed alongpanel surfaces. Power for the modulesmay be provided either by battery oraircraft, and the power switch, battery,and intensity control typically arelocated on a small box mounted near theexisting interior lights control panel.

The LED projector modulesystem is relatively inexpensive and easyto install. Given installation of sufficientmodules in proper locations, the systemgenerally can provide satisfactoryillumination of cockpit controls anddisplays. However, uniformity ofillumination is partly dependent on thelocations of existing screws on cockpitsurfaces, which in turn determine thedesign and locations of brackets andmodules. Each different cockpit typerequires a different set of custombrackets. If modules are not installed inoptimal locations, the geometry of theinstallation may result in shadowing ofsome controls or displays; in fact, slightshadowing may be difficult to avoid in apractical installation in certain cockpits.Depending on the cockpit layout, theconfiguration of the installation, and thelocation and height of the mountingbrackets, modules also may bevulnerable to damage in some locations.Filtering of warning/caution/advisoryindicators is accomplished either as inintegral lighting installations or withexternal removable filters.

External Filters

When neither aircraft wmngchanges nor NVIS compatible integralillumination are options, external filtersthat block transmission of red and near­IR may be installed over instrumentfaces. Such filters are the same size asthe clear glass windows on instruments,and typically appear light aqua in color.Unmodified integral instrument lightingis retained and used; the window simplydoes not transmit red and near-IRwavelengths. Each fIlter is mounted in athin bezel-like metal frame that may bequickly and semi-permanently installedover the face of an existing instrumentusing the existing instrument mountingscrews. No modification to theinstrument is required, and the filterframe typically adds no more than 7 mIn

to the face height of the instrument.Alternatively, the filter may bepermanently installed in place of theexisting clear glass window on eachinstrument, although such an installationmust be performed either at the point ofinstrument manufacture or at a qualifiedrepair facility. In such a case, sparesconfiguration issues will arise if allsimilar instruments in the entire supplychain have not been similarly fitted withfilter windows because, if a filteredinstrument must be replaced, thereplacement may have a clear glasswindow, making it incompatible.

When using the external filterapproach, the filter characteristics arecritical. The filter must possess goodoptical qualities to prevent distortionwhen viewing instrument or displayinformation. The filter also must exhibithigh transmission in the visible portionofthe spectrum because, during daytime,instrument illumination (and thus

5

instrument readability) is due to ambientlight. The ambient light must passthrough the filter to illuminate theinstrument face, and that portion of lightreflected by the instrument face mustpass through the filter again as it exits.Therefore, during daytime the lightreaching the viewer has been attenuatedtwice by the filter. Assuming a perfectlyreflective (diffuse dazzling white)instrument face and a filter with 50%transmission in the visible region, only25% of the incident light (50% x 50%)would exit the instrument and reach theviewer. During darkness, light from theinstrument's integral illumination mustpass through the filter only once.

Each different instrument windowshape or mounting configurationrequires a matching piece of glass,and/or a matching machined frame toensure a proper fit and to prevent lightleakage. The initial investment inexternal filters therefore may berelatively high. However, wheninstalled using metal frames, externalfilters neatly circumvent NVIS vs non­NVIS compatible configuration issues.If an instrument must be replaced, thefilter/frame simply is transferred to theface of the replacement instrument.Cockpit warning, caution, and advisoryindicators typically are addressed as inintegral lighting installations.

Chemical Light Sticks

For aircraft in which NVGs mustbe used, but in which permanent NVIScompatible lighting or filters are notinstalled, green chemical light sticksmay be used to provide temporary close­distance flood lighting. A small amountof near-IR energy is emitted by green

light sticks, and although the energy issensed and intensified by the NVG, itgenerally is insufficient to seriouslydegrade NVG-aided VA. However,reflections of glowing light sticks oftenare visible in the canopy, and NVG­aided VA usually is severely degradedwhen attempting to view the outsideworld through such reflections.

Light sticks are available inseveral sizes. 150 and 100 cm lengthsare most commonly used for cockpitillumination; a small 40 cm "fish lure"size sometimes is used for short termillumination of a small area. Each 150or 100 cm light stick is placed in anopaque cylindrical plastic holder havinga slot aperture along its length. Theeffective width of the opening, and theamount of light allowed to exit theenclosure, is varied by rotating an outeropaque plastic sheath with a similaraperture. Each plastic holder is mountednear the instrument(s) to be illuminatedand affixed to the cockpit structure orinstrument panel with VelcroTM. Thesmall 40 cm units are held in place andshrouded with black tape.

Light sticks emit light as a resultof a chemical reaction between twoliquids. Both liquids (one contained in athin glass capsule) are sealed inside theplastic body of the light stick, but theliquids are kept separate from each otheruntil the light stick is to be used. Thelight stick is 'activated' by twisting orflexing its plastic body, thus fracturingthe internal glass capsule and allowingthe liquid chemicals to mix and react.

The luminous intensity of a lightstick typically is greatest immediatelyafter activation and gradually decaysthereafter. However, similar light sticks

6

may exhibit significant differences inluminous intensity after activation, andindividual light sticks may decay quicklyor simply fail to emit light. Visible lightnormally is emitted for up to twelvehours depending on the volume ofchemicals involved, but the useful life ofa 150 cm light stick (the period duringwhich it produces sufficient light to beuseful for cockpit illumination) usuallyis limited to 90 minutes or less. Theluminous intensity of smaller light sticksdecays more quickly. Light sticks aresensitive to temperature, and coldertemperatures will significantly reducethe luminous intensity. For adequateillumination, chemical light stickstherefore must be properly located andreplaced at specific intervals.Replacement is particularly importantbecause the eye continuously adapts asthe luminous intensity of the light stickdecreases, and there is no warning thatthe instruments are about to becomeunreadable.

In keeping with the temporarynature of cockpit illumination usingchemical light sticks, warning andcaution indicators typically are coveredwith a thin, flexible green filter filmcommonly referred to as "GlendaleGreen." The film is held in place withblack tape, and is installed for nightoperations and removed for dayoperations. Those incompatible lightsources that cannot be extinguished andare not critical during flight often aresimply covered with black tape. Thefilter film substantially reduces emissionof red and near-IR wavelengths from thedisplay over which it is placed, but onelayer usually is insufficient to adequatelyblock such emission, and several layersof film over a given light source usuallyare required. When two or more layers

are used, bubbles often form between thelayers, and display readability isdegraded accordingly.

Chemical light sticks and filterfilm provide an inexpensive means ofimplementing partially NVIS compatibletemporary cockpit lighting, but for safeand effective use it is important thatoperators recognize and account for theshortcomings inherent in the approach.A dedicated installation time is requiredbefore each flight. At least 26 lightsticks (including spares) are required fora single F-16D mission, and the filterfilm must be replaced periodically due towear and degradation (bubbling andcloudiness) caused by its repeatedinstallation and removal. Recurringcosts therefore can become significantovertime.

Light Emitting Diode Illumination

In response to concerns about theadequacy and NVIS compatibility ofillumination provided by chemical lightsticks, a new interim NVIS compatibleillumination system based on lightemitting diodes (LEDs) was developedat the Air Force Research Laboratory(AFRL/HEA) at Mesa, AZ. The LEDsystem provides illumination that is fullyNVIS compatible, and has provedpopular to date. It is designed to replacechemical light sticks in temporaryinstallations.

The LED illumination systemconsists of special discrete LEDs locatedin unobtrusive locations throughout thecockpit, floodlighting the controls anddisplays. The LEDs have an estimatedminimum lifetime of 10,000 continuousoperating hours, are capable of very high

7

luminous intensity, and have a narrowbluish-green emission spectrum;virtually no red or near-IR wavelengthsare emitted. Several LEDs are mountedin a small module measuring about 25 x40 mm, and multiple modules in turn arelocated throughout the cockpit, affixedto existing structures using VelcroTM •

The modules are interconnected withthin electrical wiring that is routedinconspicuously between modules andheld in place with clamps secured byexisting screws or with VelcroTM. AllLEDs in a cockpit are powered by oneset of alkaline C-cells contained in asmall box that typically is mounted withVelcro™ adjacent to the existing cockpitlighting control panel. The LED systempower therefor~ is independent ofaircraft power. The power switch andintensity control(s) are located on thebattery box. The cable leading to theLED modules interfaces with the batterybox through a connector, allowing thebattery box to be removed for servicewithout disturbing the placement of themodules. The LED modules do notinterfere with normal instrument viewingand may be left installed in the cockpitindefinitely.

Unlike lithium cells, whichtypically exhibit a "stair-step" dischargecurve having a rapid (and oftenunpredictable) fall-off in power at theend of their useful life, alkaline cellshave a gradual, well dermed dischargecurve. By subjecting such cells to adefined heavy load and measuring thevoltage sustained across the load,remaining cell life can be predicted withreasonable confidence. To takeadvantage of this trait and predictremaining life of the alkaline cellspowering the LED system, a batterytester incorporating a switchable load

resistor, voltage comparator, andindicator is built into the battery box.Pilots may readily assess remainingbattery life before flight. Experimentaldata indicate that a set of fresh C-cellswill power an LED system for more than100 continuous operating hours with nodiscernible decrease in intensity.

In concert with the LEDillumination system, cockpit warningand caution indicators are covered with aremovable filter matrix composed ofdark green plastic filter 'tiles' bonded toa single layer of flexible green filter filmcommonly referred to as "GlendaleGreen." The film acts as the mountingsurface for the filter tiles, which are cutto size and positioned over illuminatedindicators as required. The flexibility ofthe film allows illuminated switches tobe depressed, and the film also acts as asecondary filter by blocking most near­IR energy that leaks around the edges ofthe filter tiles. The filter tiles are ofreasonable optical quality and transmitvirtually no red or near-IR wavelengths.Indicator legends viewed through thefilter tiles are easily read with theunaided eye but are essentially invisiblewhen viewed with NVGs. The filterfilm and tile matrices are permanentlybonded to the edges of lightweightplastic frames that in turn are affixedwith Velcro™ to the structures aroundthe indicators; the filter matrices areinstalled for night operations andremoved for day operations.

For cockpits with color electro­optical displays, filters of good opticalquality plastic are installed over suchdisplays. The filters suppress emissionof red wavelengths and block most near­IR wavelengths, allowing most colorcoded information to remain visible.

8

The filters are precision cut to closely fitthe display area opening in the existinginstrument bezel, and typically areaffixed in place using VelcroTM. Inallowing color information to remainreadable, the filters transmit a smallamount of red and near-IR energy.Displays therefore must remain at lowerbrightness settings in order to avoidaffecting NVG performance. The filtersare installed for night operations andremoved for day operations.

The cost of the LED systemvaries depending on the configuration ofthe cockpit and the filter requirements.Current recurring costs range from about$1000 for small cockpits having onlymonochromatic (NVIS compatible)green displays to as high as $5000 forlarge cockpits requiring multiple colorelectro-optical display filters.

Paradigms and Trends

Approximately fifteen years ago,when US military night fixed-wingprograms first were formalized, NVIScompatible cockpit lighting typicallywas approached from a paradigm ofintegral lighting. For example, integrallighting was utilized in the Navy F/A-18and Marine Corps AV-8B night attackaircraft programs from their inception,and the Navy's entire instrument sparesand logistics chain was modifiedaccordingly to support this approach.The effectiveness of integral lighting hasbeen proved over time, and some (butnot all) more recent aircraft programsalso have incorporated integral NVIScompatible lighting. However, a numberof aircraft programs currently exist inwhich night missions are flown andNVGs are used, but in which the

cockpits have yet to be equipped withpermanent NVIS compatible lighting.

The cost of any NVIS compatiblelighting system is comprised of not. justcockpit hardware, but also non-recurringengineering (NRE), documentation,installation, and support costs for the lifecycle of the system. On a per-aircraftbasis the cost of supporting a permanentNVIS compatible cockpit lightingsystem can easily outweigh the purchaseprice of the cockpit hardware alone ­which by itself can be very expensive.Previous estimates of the per-aircraftcost to install NVIS compatible integrallighting fleet-wide in a single seataircraft have run over US$100,000, notcounting NRE and support. Such figureshave become increasingly unattractive inlight of recent defense budget trends,and many aircraft programs havepostponed integration of permanentsystems while seeking more affordableapproaches. Vendors of lighting systemcomponents, having recognized thistrend, have begun offering increasinglyinnovative and less expensivealternatives. For example, the cost of apost and bezel system may be estimatedat between 20% and 30% of the cost ofan integral system. A floodlightingsystem based on modified existingfixtures can cost even less.

Regardless of the approachtaken, implementation of NVIScompatible cockpit lighting across anentire aircraft program takes time. Someaircraft programs, already tasked to flywith NVGs but scheduled to receivepermanent NVIS compatible cockpitlighting at some future date, have filledthe gap by using chemical light sticksand 'Glendale Green' filter film. Certainshortcomings associated with the use of

9

light sticks and filter film have beenknown for some time, but until recentlyno other temporary source of (almost)NVIS compatible light was available.Recent development of the temporaryLED-based lighting system, directed bythe Air Force Research Laboratory,proved that NVIS compatible lightingneed not be costly. Although onlyintended to be a temporary expedient,the success of the LED system to datehas caused a shift of previous paradigmsconcerning design of NVIS compatiblelighting systems. Customers now expectaffordability in addition to performance,and out of necessity these expectationshave been (and will continue to be) astimulus for further innovation.

Many aircraft with legacycockpits having incompatible lightingwill remain flying for years to come, andincreased use of NVGs will drive acorresponding demand for affordableNVIS compatible cockpit lightingsystems. The gradual transition of nightvision devices into civilian aviation,which just has begun in the US, maymake the cockpit lighting and pilottraining issues currently faced by themilitary appear minor compared to thoseengendered by the diversity of civilianaircraft types involved. The cockpitlighting methods being developed andlessons currently being learned shouldprove useful in the future.

Methods of Implementing NVISCompatible Cockpit Lighting

John J. Martin

Raytheon Systems Co.

supporting

Air Force Research Laboratory

Warfighter Training Research Division (AFRUHEA)

Mesa, AZ 85212

NVIS: Night Vision Imaging System

Night vision goggles (NVGs) are very sensitive to lightfrom any source.

Int~nsified. imagery of the outside scene is of primaryimportance to the pilot. It is undesirable for NVGs tosense and intensify light from any sources other thanthose in the outside world.

Light from cockpit sources that is detected by the NVGwill be intensified and may reduce NVG gain, thusdegrading the image quality of the outside scene.

• NVIS compatible lighting results in instruments and displays beingeasily read with the unaided eye at night, while at the same time ...

• NVIS compatible lighting is not sensed by and generally is invisible tonight vision goggles

• NVIS compatible lighting is implemented by tailoring cockpit lightingso instruments and displays only emit wavelengths to which the eye ismost responsive; little red and no near-IR emission

• Filters integrated in NVG objective lenses pass only deep red and

near-IR wavelengths, blocking all other wavelengths and making the

NVG 'blind' to them

• Ideally, cockpit spectral emissions and NVG spectral response aremutually exclusive

• Permanent

- Integral (internal) instrument I display lighting

- Post and bezel lighting

- Flood lighting using existing aircraft light fixtures

- Flood lighting using LED-based light sources

- External filtering

• Temporary

- Chemical light sticks

- Light emitting diodes

• Internal light sources in instruments that are filtered or modifiedto emit no red or near-IR energy. Implemented duringmanufacture, or retrofitted at a qualified instrument repair facility.

• Usually provides excellent illumination; light sources are optimallylocated in instrument design.

• Requires no aircraft wiring changes.

• When unpowered, an integrally illuminated NVIS compatible instrument

externally appears no different from an incompatible instrument.

Labeling is important.

• Supply chain spares and logistics issues arise if all similar instrumentsare not also NVIS compatible.

• Small NVIS compatible light sources, external but immediatelyadjacent to the instrument faces.

• A bezel surrounds an instrument, contains light sources aroundperimeter, usually covers instrument face with a special window thatdirects light inward.

• Post lights stand out a short distance from panel, directing light downtoward instrument face. Careful location is required in order to avoidreflected glare.

• Very close range of lighting (particularly with bezels) results in ashort "throw distance." Design is important in achieving uniformillumination.

• Requires aircraft electrical system changes (and sometimes drilling).

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• NVIS compatible light sources, external to (and usuallysome distance away from) instruments, strategicallylocated throughout cockpit. Existing fixtures and/orlocations typically are used.

• . Relatively inexpensive and easy to retrofit. Implementation may

be as simple as substituting new filter glass in place of existing

clear glass.

• Requires no changes to conventional instrument illuminationsystem, usually no wiring changes.

• Potential shadowing problems (sometil:nes severe) and reflectedglare from specular surfaces in cockpit.

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• NVIS compatible light produced by multiple Light Emitting Diodebased sources in enclosures strategically located throughoutcockpit.

• Relatively inexpensive and easy to install. LED-based sources aremounted with brackets using existing screw locations, interconnectedwith dedicated wiring. Powered by battery or aircraft electrical system.

• Independent permanent system, requiring no changes to conventionallighting system. Existing instrument lighting simply is extinguished.

• Potential for shadowing or non-uniform illumination depending onlocation of sources. Also possible vulnerability to physical damagedepending on bracket height and location.

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• Special glass filters, mounted in metal frames, semi-permanently

affixed over faces of existing (unmodified) instruments usingexisting screws.

• Filter is of high optical quality, does not transmit deep red andnear-IR. Filter color appears light aqua to the unaided eye.

• Existing internal instrument lighting is used.

• No aircraft wiring changes are required.

• If instrument repair and exchange is required, filter is transferredfrom old instrument to replacement instrument. No dissimilarspares issues.

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• Temporary source of illumination, currently used in aircraft forwhich permanent lighting installations are not available.

• Light sticks emit light as a result of a chemical reaction between twoliquids. Light sticks are placed in tubular holders, affixed with Velcro1M

near instruments.

• Emission is green, with slight 'tail' into the red. Energy is sensed andintensified by NVG, but adverse effects usually are minor.

• Direct reflections of light stick emissions may be visible in canopy.NVG image of outside world is severely degraded in these areas.

• Intensity peaks shortly after activation, then gradually diminishes.

• Replacement at specific intervals is important. The eye continuouslyadapts as luminous intensity of light sticks slowly decreases, and thereis no warning that the instruments are about to become unreadable.

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Temporary system for use where permanent systems are unavailable.

• Inexpensive, easily installed. (Roughly 90 minutes to install in F-16.)

• LEOs used are capable of very high intensity, emit bluish-green light withvirtually no red or near-IR spectral components.

• Multiple LEOs are grouped together in small modules. Modules are locatedon cockpit side walls and/or adjacent to instruments, affixed with Velcro TM.

'String' of modules is interconnected with small wires.'l

• Powered by one set of alkaline C-cells, independent of aircraft power.Estimated 100+ continuous operating hours on one set of fresh C-cells.

• Battery box incorporates power switch, battery tester, intensity control(s).Removable, typically located near existing interior lighting control panel.

• Potential for shadowing or non-uniform illumination depending on locationof modules. Modules also may be vulnerable to physical damage.

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