LEDs for Aircraft Passenger Reading Lights
Experimental setup of a mock airplane cabin with reading lights.
LRC researchers install and test fixtures in an adjustable-height false ceiling.
LED Reading Light Study
Light-emitting diodes (LEDs) have been used in niche aircraft lighting applications, such as "No smoking" and "Fasten seatbelt" signs, for quite some time. Recent advances in white LED technology have prompted aircraft manufacturers to consider LEDs for more general cabin lighting applications, which could reduce onboard energy consumption. The passenger reading light is one such application. However, the question remains whether white LEDs are ready for use in passenger reading lights, including whether they can meet current standards and will be acceptable to passengers.
This study investigated the performance of LED and traditional halogen passenger reading lights to identify the key operating characteristics for good performance, regardless of lamp type. Three LED fixtures were evaluated and compared with 12 halogen fixtures for compliance with current standards, performance characteristics, and user acceptance.
An experiment was designed to test the compliance of LED and halogen reading lights with national standards set by the Society for Automotive Engineers (SAE). SAE has established minimum and maximum illuminance requirements for various points on a target surface below the reading light, such as a tray table. LRC researchers mounted halogen and LED test reading lights one at a time into an adjustable-height ceiling. A pattern of the SAE measurement points was placed on a target surface, and the test fixtures were aimed straight down toward the center of the pattern. A calibrated light meter was used to take illuminance measurements at each point.
Passenger Opinion Survey
The passenger opinion survey evaluated subjective preferences for LED and halogen reading lights. Four aircraft passenger seats were installed in a small room to create a miniature, mock aircraft cabin, and reading fixtures were installed above each seat. Sixty subjects completed computer, reading, and color discrimination tasks under each fixture and rated their color, brightness, and color-rendering properties.
All reading lights tested met the SAE guidelines; however, the beam patterns and quality of each were significantly different. The light levels produced by the reading lights were also much different, which can be attributed to the large tolerance range that the SAE specification allows. An analysis of the beam profiles showed most of the fixtures to have nonsymmetrical beam patterns, meaning that certain parts of the beam were brighter than others, rather than there being an even spread of light. Spectral measurements indicated that the halogen and LED fixtures may appear different when viewed side by side. Furthermore, LED systems tend to create a white beam surrounded by a blue ring; this characteristic was quite noticeable in one system tested. Power measurements showed that all three LED fixtures used half as much energy as the halogen fixture.
Passenger Opinion Survey
Overall, subjects preferred the halogen reading light in terms of comfort and skin tone appearance, but disliked its yellowish color. They preferred the LED fixtures for helping them to see more clearly, but at the same time found the LED fixtures to be generally too bright and too blue or green, creating unnatural skin tone colors.
Manufacturers can easily remedy many of the problem areas noted by selecting LEDs with more appropriate color and by modifying the optics. However, further research is needed to determine the optimum color for aircraft reading lights.
Given future improvements to the fixtures and LED technology itself, LEDs will become a promising lighting option for commercial aircraft. LEDs have the advantage of being twice as efficient as halogen and offering lower replacement costs due to longer life. However, results from the passenger opinion surveys suggest that the current design guidelines for passenger reading lights may not be sufficient to ensure a good quality light. Current SAE guidelines are based on halogen technology and do not have the level of specification needed for an LED implementation. Modifying the SAE specifications to include color, edge effects, glare, long-term performance, and energy consumption could improve the quality of passenger reading lights, regardless of the type of light source.
Alliance for Solid-State Illumination Systems and Technologies (ASSIST)