Airfield lamps an introduction

Friars Marketing Airfield Lamps +44 (0) 1858 463153 supply European and American airfield lamps used in current and obsolete fittings.

The product range contains Osram, Philips, GE, Sylvania, Radium and Genesis airfield PK30d lamps, airfield cold beam reflector lamps, airfield single and double-ended lamps, airfield tungsten halogen lamps, airfield IRC lamps, airfield PAR lamps, and airfield Xenophot lamps.

Cold beam reflector lamps prevent heat from being concentrated on optical parts of luminaires such as filters, lenses or prisms.

Osram airfield double ended tungsten Halogen lamps Tungsten halogen lamps can be operated well below rated current with intensities well below full intensity and are the light source of choice in all visibility conditions, day or night.

Their small bulb dimensions and high luminance enable compact lights to be constructed with low protrusion over ground.

Because 60% of the radiation from airfield lamps is infrared (IR) rays, airfield IRC lamps increase the efficiency of halogen lamps by reflecting a major part of the generated IR radiation back to the coil where it is converted into visible light.

The infrared reflective coating on the outside of the burner acts as an IR mirror but lets nearly 100% of visible light pass.

In comparison to standard halogen lamps it is possible to optimise the lamp in different directions by using more light output for less electrical power with an increased lifetime.

In airfield Xenophot lamps, xenon is the filling gas which increases the luminous efficacy making it easier to comply with the international standards and recommended practices of aviation authorities.

They generate more light output for the same power consumption than their krypton counterparts.

Airfield Lamps and Their Functions

All inset lights in runways and pavements have specific uses and all use different colors to signify their purpose. The colors are obtained by using absorption filters or lenses.

The emissivity of each color varies. This highest value is white (100%), followed by yellow or amber (55%), red (23%), green (21 %) and blue (3%). Using dichroic filters can increase these values for certain colors.

White airfield lamps are used for signals that have the longest range, such as the runway centerline, runway edge, touchdown zone and approach lights.

Taxiway centerline, high-speed-exit and threshold lamps are all green. Taxiway-edge lights are blue. The conventional codes, red for "danger-do not go" and yellow for "caution" are followed.

Threshold-end lights facing upwind signal that the end of usable runway is approaching.
Yellow hold-bars warn of impending intersections. In the United States, red hold-bars are not used unless the red can be switched to green or off. There are variations, such as using yellow at the intersection of taxiway centerlines.

Helicopter pads and apron boundaries are sometimes marked by yellow lights. Turn-offs from runways onto taxiways are usually designated by a double blue edgelight, but an amber light at this location is sometimes used. Dead ends and forbidden entry are always shown in red.

At times, a secondary color accompanies the regular color to convey a special message. For example, runway centerline lights set 2000 feet before the runway's end are alternate red and white and then all red for the last 1000 feet.

Similarly, edge lights are amber for the last 2000 feet of the runway, signifying to pilots that usable runway is running short. Approach lights use bars of red lights to signal the closeness of the threshold in Category II and III configurations.

Flashing lights are seldom used, but when they are, they alert a pilot to a special condition. These are usually amber and should not be confused with sequenced, white high-intensity discharge lamps used on approach and runwayend identifier lights (REILS).

The latter are sometimes installed as inset fixtures if the threshold is displaced.
Lights can be unidirectional, bi-directional and omnidirectional. Touchdown-zone lights are always unidirectional, as are approach lights.

However, in some countries and some smaller GA airfields, low-intensity and/or medium- intensity omni-directional approach lamps are employed for VFR use.

European airports switch between high and low intensities,
using a single fixture that houses lamps of both intensities. The omnidirectional lamps provide better circling guidance.

Hold lights and high-speed-exit lights are usually unidirectional. Most taxiway centerline lights and runway centerline lights are bi-directional.

Taxiway intersection lights (and sometimes inset taxiway edge lights) are omnidirectional. Some lights are not only bidirectional, but they also include different colors for each direction.

An example is threshold lights, which are green downwind and red facing the runway.

Problems Posed to Airfield Lamps By Water and Moisture

The truism that water and electricity don't mix holds for airfield lamps and inset lighting. Since airport pavement is subject to many sources of moisture, the developers of monolithic systems needed to prevent water and water vapour from making contact with the electrical conductors, contacts and connections. In addition, the lamps used in the fixtures may be damaged by water that touches their hot surfaces.

Early attempts to seal water from the light bases and lights employed flat gaskets and "o" rings. These attempts succeeded only partially because moisture in the form of condensed water vapour (which is almost always present in the air) quickly found its way into the light fixture through the conductors, or through small apertures in the seal of the lenses, which caused corrosion of the light's contact fittings.

Some gradual advances were made in controlling moisture in 1965, when manufacturers of inset lights developed seals that prevented moisture from entering the light fixture.

Waterproof connectors made connections of the lights and transformers possible without fear of electrical shorting to ground. Although these developments made inset lights more dependable, water within the light bases still created problems.

Leakage is especially undesirable in colder climates because of damage done when water freezes, forms into ice and then expands.

Experimentation showed that inserting a small block of polyurethane foam prevented damage done to the light fixtures by the expanding ice. Earlier moderately successful attempts to keep water out of bases used "o" ring seals between the light fixture and the base.

Still, poor maintenance of the "o" ring seals, dirt in the "o" ring grooves and loosening of the holddown bolts allowed water to enter. It could also enter through the conduit system.

Systems using devices to seal out water are known as "dry systems" and are still used in areas with high water tables. Around 1975, installations known as "wet systems" were developed.

These systems negate the entrance of water by draining the bases through conduit stubs in the subbase. The stubs are located at low spots and allow water to drain to lower elevations at the sides of the pavement.

Another common "wet system" merely drains the light base with a pipe passed through the bottom of the base down into the subbase or a French drain.

This method depends on the percolation of the subsoil. Care must be taken to assure that weaknesses in the subbase are not washed out to form voids, which can then weaken support of the light and of the
pavement.

Airfield lamps and danger

Inset lights and the light bases that support them, must be as strong and durable as the pavement of which they are a part.

A variety of stresses affect both the pavement and the lights: stresses imposed by dynamic impact; by static, torsional and hydraulic loads; by temperature differentials; and by abrasion and corrosion.

Although designing the lights and bases to resist these stresses is fairly simple, periodic inspection and maintenance are still critical in preventing failure or diminished performance.

Some soils are more corrosive than seawater. An overall coating of coal tar emulsion properly used and installed will give protection in those kinds of soils.

The bases exist in a corrosive environment. Like any other steel structures, they must be inspected and maintained.

The stainless steel bolts that hold the light to the base are subjected to many stresses, not the least of which is the torque tangentially applied by the impact of aircraft wheels or by the twisting action produced by a heavy aircraft's locked wheel during a turn.

Loose bolts are an unwanted danger since they are easily sheared or lost, which increases the chance of losing the light fixture and thus creating a hazard to the operation of the airport.

In 1975, special locking devices were introduced to lessen the chance of bolts loosening from vibration and shock.