Interior Illumination

Interior Illumination Shedding some light on the subject By Joe Escobar April 2001 In today’s aircraft, lighting plays an essential role. We are aware of outside lighting requirements such as position and anti-collision...

Halogen lighting
There has been an increase in use of halogen lighting in aircraft interiors. Halogen bulbs are basically incandescent bulbs with a few differences. In a halogen bulb, a process known as the halogen cycle helps to extend the life of the tungsten filament. Halogen is added to the gases inside the bulb. As the tungsten evaporates and settles on the inner surface of the bulb, the halogen chemically reacts with it and forms tungsten halides. When these halides reach the filament, they break down, and the tungsten is redeposited on the filament.
One company that has adapted halogen bulbs for aircraft applications is LaVerne, California- based DPI Labs. They have recently developed a color-corrected halogen light. Instead of using a traditional aluminum reflector, they use a diachrillic reflector for their bulbs. This reflector allows infrared light to escape out the back of the light assembly while allowing the light to be reflected forward. This results in a cooler, brighter beam than standard incandescent lamps. These bulbs can be used for many applications from reading lights to directional lighting.
Because of the high temperature at which halogen lights operate, care needs to be taken when handling them, as handling a recently operated bulb can result in burns. Also, when handling unprotected halogen bulbs, technicians should avoid touching the glass of the bulb with their bare hands. Oils and salts from the hands can carbonize on the quartz glass of the bulb. This leaves a dark spot that absorbs radiation from the filament and becomes extremely hot, possibly causing the bulb to crack or shatter.

Fiber optic lighting
Another technology that is seeing increased use in interior illumination is fiber optics. Avtec, Inc. based in Cahokia, Illinois is a manufacturer of aircraft fiber optic lighting systems. Their system is used for upwash / downwash, galley, and accent lighting applications.
Fiber optic systems are made up of two major components — the illuminator and the fiber assembly. The illuminator is the part of the system that produces the light. Avtec’s product consists of a 60-watt lamp, ballast, cooling fan, end even color wheels to allow for change in lighting color. The fiber assembly of the system is the part that actually gives off the light. The fiber assembly starts with a lead-in section covered by heat shrink to prevent light loss. This section goes from the illuminator assembly to the area where lighting is required. From there, the illuminated section of fiber provides light along its entire length and is terminated with an end cap. One illuminator is able to illuminate 45 feet of fiber with up to 25 feet of lead-in cable.
Fiber optic lighting offers several benefits. First of all, there are less bulbs involved to change out. The lighted cable is cool to the touch and is durable. It is also flexible — allowing for a minimum bend radius of 4.0 inches. About the only required regular maintenance is cleaning the fiber with a mild soap and water solution. As with any plastic, subjecting the fiber to harsh solvents can damage it — causing decreased light output or even necessitating replacement.

LED lighting
Light Emitting Diode (LED) lighting technology is emerging as one of the most widely researched methods of illumination and has made its way into aircraft lighting. As the name implies, an LED is basically a diode that emits light when electricity flows through it. Although LEDs have been around for quite a while, white LEDs have not been available until recently.
Many different companies are developing LED lighting systems. Whelen, a Chester, Connecticut company, has developed an overhead LED light that gives off a bright light while at the same time offering a lower profile and cooler operating temperature than other types of lighting. They are also developing LEDs for other uses including post lights and exterior position lighting.
Muskego, Wisconsin-based EMTEQ also offers overhead LED light assemblies. In addition, they have a unique LED product in the form of flexible and semi-flexible tube lighting. As the name implies, their product is a series of LEDs encased in a plastic tubing that is flexible enough to bend around contours. This offers interior refurbishing companies as well as OEMs more "flexibility" when addressing lighting issues.
B/E Aerospace is another company that is developing LED lighting products. They offer LED reading lights as well as a Smart Dimmer Control Panel, which is capable of controlling up to four cabin lighting zones independently with memory.
LEDs offer many advantages including extended life (usually up to 100,000 hours of operating life) and solid state design (no glass to shatter or filaments to break). They also consume 10 percent the current draw of conventional lights at the same light output. Many new applications are being developed for these lights, and their use is becoming more widespread.
Rod Stoehr of B/E Aerospace points out that where LEDs are concerned, even though they have a long life, it can be significantly shortened if they are operated at temperatures higher than their design specification. Be careful to chose LED products from a reputable manufacturer that has taken this issue into consideration. Also, as with a regular diode, when installing an LED, it can only be installed in one direction to work properly. This needs to be kept in mind whenever replacing LEDs.

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