11.14 Lights

Aircraft Lighting Overview

• Lighting is crucial for aircraft safety, aiding in emergency exit illumination and pilot visibility during landings, especially in poor conditions.
• Engineers need a thorough understanding of light production, the purpose of various aircraft lights, and their operation.

Typical Aircraft Light Sources

• Electric light sources commonly found in aircraft include:
  • Incandescent Lamps
  • Halogen Incandescent Lamps
  • Gas Discharge Lamps / Strobe Lights
  • Light Emitting Diodes (LED)
  • Luminescent Lighting
• Light is generated through thermal radiation (incandescence).
• A high current passes through a conductor, heating it to radiate light; higher temperatures result in increased radiation.

Light Intensity

• Light output is often related to the wattage or power consumed by the light source.
• Luminous intensity is measured in 'candles' or 'candela', originally based on the intensity of a standard wax candle.
• Luminous flux is the total amount of light radiated by a light source per second.

Incandescent Lamps

• Incandescence is the emission of visible radiation from a hot body.
• Electric lamps produce light by heating a metallic filament with an electric current until it glows.
• Aircraft lamps are typically rated at 5 V, 12 V, and 28 V; lower voltage lamps provide greater light intensity for the same power consumption due to thicker filaments.

Incandescent Lamp Details

• In incandescent lamps, the filament gradually thins as tungsten atoms evaporate and deposit on the glass enclosure, causing darkening.
• This thinning weakens the filament until it breaks.
• Inert gases like nitrogen and argon are used to reduce tungsten sublimation and extend filament life.

Halogen Incandescent Lamps

• Halogen bulbs extend filament life using chemically active gases (iodine, bromine, chlorine, and fluorine) to prevent "lost atoms" from depositing on the bulb.
• Halogen bulbs operate at high temperatures and must not be touched with bare hands.
• Grease and salts from skin can weaken the aluminosilicate glass, causing shorter life and surface darkening.

Strobe Lights

• Stroboscopes emit brief, intense flashes of light at specific intervals.
• Used for anti-collision and beacon lights on aircraft, with a flashing frequency of 40-100 cycles per minute.

Light Emitting Diodes (LED)

• LEDs release energy as photons when an electric current passes through them.
• The wavelength of light, and thus its color, depends on the LED material.
• Materials emit visible or near-ultraviolet light.

LED Advantages

• LEDs have several advantages:
  • Reduced mass (approx. 30%)
  • Reduced power consumption (approx. 50% to 75%)
  • Longer lifespan (3 to 15 times more than incandescent or fluorescent lights)
  • Resistance to knocks and vibration.
• These advantages lead to substantial cost savings in materials and maintenance.
• A disadvantage is that operating temperatures above 80°C drastically reduce LED service life.

External Lighting Purposes

• Aircraft external lighting enhances visibility during air and ground operations.
• Providing sufficient view for the crew to operate safely.

External Lighting Types

• External lights include:
  • Navigation lights
  • Anti-collision lights
  • Landing lights
  • Taxi/turn-off lights
  • Taxi lights
  • Ice inspection lights
  • Logo lights
• Lighting systems are governed by Certification Specifications for Large Aeroplanes CS25, which sets minimum requirements for candela, flashing rates, and color.

Navigation Lights

• Navigation lights indicate an aircraft’s position and orientation.
• Mandatory lights include:
  • Red light: Visible from directly ahead to 110° to the left.
  • Green light: Visible from directly ahead to 110° to the right.
  • White light: Visible from directly to the rear of the aircraft.
• Must be visible with specific light intensity and color.

Navigation Light Positions

• Navigation lights are installed at predetermined locations:
  • RED = Left/Port wing tip
  • GREEN = Right/Starboard wing tip
  • WHITE = Tail light (position varies)
• Lights can be switched on via a two-position switch, using AC in flight and DC on the ground.

Navigation Light Systems

• Simple systems operate via a switch connecting the main busbar to the lights.
• More complex systems use a flasher unit for a switched or flashed output.

Anti-Collision Lights

• Anti-collision lights attract attention with a flashing light to enhance aircraft visibility.
• Typically on the upper and lower fuselage or wing tips.
• Can be incandescent filaments or xenon strobes, powered by 12 V, 28 Vdc, or 115 Vac.

Anti-Collision Light Types

• There are two basic types:
  • Rotating beam
  • Flashing lights
• Mandatory lights that mark the aircraft’s position, working with navigation lights.

Rotating Beam Lighting

• Rotating beam units use a steady light directed into a beam.
• A reflector rotates via an electric motor.
• Rotational speed is normally 40-45 RPM, resulting in 80-90 flashes per minute.
• Covered by a red lens.

Rotating Reflector Type Beacon

• Motor-driven with a small motor rotating the reflector past the bulb.
• Available in 28 Vdc and 115 Vac varieties.
• An example is a Grimes 28 Vdc unit flashing at 60 times per minute.

Fixed Reflector Type Circuit

• The flash is produced by an electronic flasher unit that rapidly switches the light on and off.

Strobe Lighting

• Strobe lights use small quartz or glass tubes filled with xenon gas.
• DC power is converted to 400 Vdc for operation, with a typical flashing frequency of 60-70 flashes per minute.
• Capacitors store and release electrical charge across a gap inside the gas-filled tube to produce a bright flash.

Strobe Light Warnings

• Stroboscopic effects can induce fits and make moving objects appear stationary or slower.
• High-intensity light can damage the eye.
• Capacitors can reach high temperatures; ensure they are discharged and cooled before maintenance.

Landing Lights

• Landing lights are mandatory to illuminate the area ahead of the aircraft during final landing stages.
• Typical positions include wing leading edges, undercarriage legs, and flap track fairings.
• Some units are fixed; others are retractable.

Landing Light Details

• Landing lights provide an intense, narrow beam of white light at a fixed angle.
• Typically powered by 28 Vac or DC, around 600 W.
• Switch contacts must handle surge currents up to 15 times the normal value.
• Landing lamp systems become very hot, with limited operation time on the ground without airflow.

Taxi/Turn-Off Lights

• Taxi lamps illuminate the path for maneuvering on the ground in darkness or poor visibility.
• Similar to landing lamps but with a lower power rating (typically 250 W).
• Mounted on the front of the fuselage or nose undercarriage.
• Turn-off lights assist with runway and taxiway turn-offs in low visibility, installed at an angle to the aircraft’s axis.

Ice Inspection Lights

• Direct a beam of light onto the wing leading edge and engine intake lip to inspect for ice formation.
• Usually mounted on the side of the fuselage, flush-mounted, and fixed in direction.
• Power supply is 28 Vac or DC, with lamps typically rated between 60 W and 250 W.

Wing Illumination Lights

• Also known as wing-scan lamps, allow for the visual inspection of wing leading edges and nacelles for ice formation.
• Located on the left and right sides of the aircraft fuselage, forward of the wings, and sealed aerodynamically.

Logo Lights

• Illuminate an aircraft’s vertical stabilizer.
• Used for ATC identification of livery, airline promotion, and easier determination if the aircraft has crossed the runway threshold.
• Often installed on the upper surface of the horizontal stabilizer or the inboard side of a fairing on the wing's trailing edge.

Internal Lighting - Overview

• Internal lights enable safe aircraft operation, effective cabin crew duties, and passenger comfort.
• Lighting categories include emergency, main, and standby.
• Divided into flight compartment, passenger compartment, service, and emergency lighting.

Regulations

• Instrument lights provide sufficient illumination for instruments and switches to be easily readable.
• Direct rays must be shielded from the pilot’s eyes, with no objectionable reflections.
• Intensity must be controllable.

Dimming Control - Incadescent

• Methods for manual control include:
  • A potentiometer
  • A transistor with a Zener diode
  • A transformer with pulse width modulation.
• Potentiometers reduce voltage across the lamp for small numbers of lamps.

Transistor Illumination Control

• A power transistor is used instead of a resistor.
• Potentiometer controls only the small base current of the transistor.

Illumination Level Control with a Zener Diode

• Uses a Zener diode to drop the voltage for bright and dim levels.

Illumination Level Control with a Transformer

• Transformers minimize internal power loss for AC-fed incandescent lights.
• Certain circuits have dimming controls.

Cockpit Lighting

• Instrument lighting ensures cockpit instruments are readable during all ambient lighting conditions without glare or reflection.
• Achieved through integral lights or floodlighting.
• Floodlighting includes reading lamps and pedestal lamps, with brightness controlled by dimmer switches.
• Automation via photosensitive cells is also employed.

Storm Lighting

• Overrides dim functions to bring all lights to full brightness during stormy conditions.
• Dimmers on cockpit lights must be at their minimum position during maintenance to prevent excessive heat build-up.

Dome Lights

• Provide general area and emergency lighting.
• Typically 28 Vdc incandescent or LED units, controlled by a three-position switch (On, Off, Dim).

Map Reading Lights

• Also known as utility or wander lights, are dimmable with white or red light, and can be focused.
• Can be fixed or removable with a coiled lead.

Instrument Lighting Types

• Integral, wedge, pillar, bridge, trans-illuminated panels, glare shields, and floodlighting.

Glare Shield

• Prevents natural light from ‘whiting’ out instruments and reflects panel lighting downward.

Wedge Lighting

• Relies on light reflecting and passing through two polished wedge-shaped pieces of glass.

Pillar Lighting

• Employs a miniature center contact filament lamp inside a housing.
• Commonly used in standby magnetic compasses with brass cases and contra-wound filaments to prevent magnetic interference.

Bridge Lighting

• A multi-lamp development of pillar lighting with two or four lamp housings fitted to a bridge structure.

Trans-Illuminated Panels

• Bonded layers of acrylic plastics with facets cut out for illumination.
• Usually 5 V, 12 V, or 26 V, and controlled by a rotary dimmer switch.

Floodlighting

• Provides general illumination for instruments, control panels, pedestals, and flight deck flooring.
• Uses LEDs, incandescent lamps, or fluorescent tube units.

Flightdeck Warning and Indication Lights

• Central Warning System (CWS) and Crew Alerting System (CAS) provide alerts.
• Urgency is indicated by color: red for immediate action, amber for less urgent action, and white, blue, and green for advisory alerts.

Alarm Categories

• WARNING: the highest priority alert
• CAUTION: the second priority alert
• ADVISORY: the third priority alert
• STATUS: the fourth priority alert

Master Warning System

• Indicates a fault in any one system via the Master Warning Lights (MWL) or Master Caution Lights (MCL).

Functional Checks

• Lighting allows for serviceability via "press to test".
• A master test switch enables checking all lamps together, testing filament and wiring integrity, not the system's full function.

Master Caution System

• Installed at pilot’s eye level in aircraft with widely monitored systems.
• Cancelable by pressing on the light cap to indicate the next fault.

Cabin Lighting

• Passenger cabin lighting enables crew duties and provides a safe, comfortable environment.
• Dependent on aircraft size and decor.
• Often utilizes indirect "wash lighting".
• Includes a night lighting mode for softer illumination.
• Next-generation aircraft use LED lighting with changeable color schemes.

Cabin Management System (CMS)

• Interfaces cabin controls (illumination, passenger signs and calls, galley and lavatory controls, and cabin intercommunication devices).

Gas Discharge Lamps

• Utilize fluorescence, where EM radiation is stimulated by incident radiation and persists while the stimulating radiation continues.
• Fluorescent lamps filled with mercury gas produce ultraviolet radiation, converted to visible light by a fluorescent material.

Gas Discharge Lamp Starter Unit

• Needs a very high voltage of several kilovolts to start light generation. Not suitable for modern aircaft.

Fluorescent Lamp Disposal:

• Contain hazardous mercury, requiring proper disposal such as recycling or hazardous waste collection.

Gas Discharge Lamps Types

• Aircraft lighting equipment has the following types of gas discharge lamps:
  • Cold start fluorescent lamps
  • Direct start fluorescent lamps
  • Strobe lights

Cold Start Fluorescent Lamps

• Require approximately 450 V ignition voltage.
• A ballast unit coil limits the lamp’s current, typically supplying two lamps.

Direct Start Fluorescent Lamps

• Electrodes are constantly heated.
• A metal strip supports ignition, and a coil limits current.
• Coil impedance can vary for different light levels using magnetic amplification.

Passenger Compartment Lighting Features

• Types range from ceiling-mounted incandescent lamps to fluorescent fittings or LEDs in ceilings and side walls for concealed lighting effects.
• Lights are also provided at passenger service units, galleys, lavatories, and for essential passenger information signs (e.g., “Fasten Seat Belts”).

Cabin Lighting Control

• Essential passenger information signs are usually controlled from the flight deck.

Examples of Where Lighting is Used

• The types of lighting can vary from a small number of ceiling-mounted incandescent lamp fittings to many fluorescent fittings or LEDs located in the ceilings and side walls to produce the desired concealed lighting effects and satisfy the functional requirements.
• Fluorescent or LED: General, indirect, and concealed lighting controlled by the attendant’s panel and equipped with an altitude pressure switch.
• Incandescent Lighting or LED: Soft low-level lighting in ceilings, work areas, etc.
• "Lavatory Occupied" signs are operated automatically by the lavatory door lock switch.

Other Cabin Lighting

• Control of the “No Smoking”, “Fasten Seat Belts”, and “Return to Seat” signs is typically by the pilot’s three-position sign control switch with ‘Auto’, ‘On’, and ‘Off’ selections.

Flight Deck Door Switch

• Ceiliing light aft of the door goes off when you open to avoid reflection. Uses a magnetic reed type switch.

Lavatory Lighting

• Dome lights are always on when electrical power is supplied.
• Additional lighting, including fluorescent mirror lights, is door latch switch controlled.

Overhead Reading Lights

• Are designed to enable the passengers to read.
• Can be incandescent lights or LEDs.

Cargo Bay Equipment Bay Lighting

• The cargo bays and equipment bays of an aircraft are normally equipped with lighting systems to provide illumination.
• Consists of lighting units in the ceiling, controlled from a switch near the entrance, and powered by 28 Vdc.

Safety Features of Bay Area Lighting

• To protect the bulb from damage during cargo loading and to protect baggage from the heat of a bare incandescent or halogen bulb, cargo lights are covered by tempered glass.

Service Lighting

• Service lighting is fitted to some aircraft to provide general illumination.
• Areas are wheel wells, air conditioning compartments, tail cones, APU compartments, electrical and electronic equipment centers, and fueling panels.

Emergency Lighting - Overview

• Passengers must easily identify safety equipment and exit routes in an emergency.
• Emergency lighting is mandatory on all aircraft.
• Regulations vary depending on passenger capacity and aircraft type.
• Gives light:
  • In the aisles
  • To identify exits
  • To identify routes to the exits
  • Outside the airplane at the slides
• Lower level than normal cabin lighting, it is powered by an independent battery.

Control

• The system is controlled by a switch on the flight deck or on the pursers' panel, and can be set to one of three positions:
  • OFF
  • ON
  • ARMED

Power

• Emergency lighting power supplies are self-contained, rechargeable battery packs providing 28 Vdc.
• Each battery pack powers a group of emergency lights, for a duration of 10-20 minutes.
• Recharge time is upwards of 16 hours.
• Charging takes place when the control switch is in the ‘Auto’ and ‘Off’ positions.

Interior Emergency Lights

• Provide general illumination in the cabin and specific illumination for exit signs, escape slides, and emergency exit hatches.
• Also have illuminated escape paths.

Floor Proximity Lights

• Used to show passengers the nearest exit.
• Lights are at floor level and may be installed in seat tracks or attached to seat support structures.
• Some have arrows on the lenses which point to the nearest exit.

Self-Illuminating (Luminescent) Lighting

• A light source that uses no electrical power but emits light continuously.
• Typical aircraft application is the self-illuminated exit sign powered by radioactive tritium gas (GTLS) in plastic containers.

Electrical Emergency Exit Signs

• Illuminate either when switched ‘On’ or when there is a power failure.

Electroluminescent Lighting

• Light emission results from applying an electric field to a material (usually solid).
• Consists of a thin laminated structure with a phosphor layer between two electrodes, one of which is transparent.

External Emergency Lights

• Slide and over-wing lights are flush-mounted near each door and emergency exit, illuminating exit areas, slides, and escape routes.

Emergency Lighting Operation

• Are fed from battery packs, which are trickle charged from the aircraft's main electrical system.
• Switch is located on the flight deck and has three positions being:
  • OFF: The battery packs are charged. 6 V lights remain ‘OFF’ even in the event off main electrical power loss.
  • ARMED: Is the normal in-flight position of the switch. A warning light, ‘NOT ARMED’ is displayed if the switch is in the ‘OFF’ or ‘ON’ position during flight.
  • ON: The battery packs are not charged. 6 V lights ‘ON’ even though main electrical power is available and normal lights are also ‘ON’.