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Airfield Lighting
of in-ground luminaires as a function of
inconsequential to many end users, airfield
How can we move toward a
definition of useful life?
luminaires are meant to provide meaningful
Understanding the long-term performance of
included three red/white directional runway
visual guidance to pilots under different
LED-based airfield luminaires under realistic
centerline luminaires (type L-850A) and three
conditions, but particularly in low visibility.
conditions is the first step to establishing a
white touchdown zone luminaires (type
Thus, airfield luminaires can only be
functional definition of useful life. With this
L-850B). In total, the luminaires were tested
considered useful if they meet all their
objective in mind, the Lighting Research Center
for more than 10,000 hours between October
photometric requirements at all times.
began a long-term study in the autumn of
2011 and January 2013.
These requirements include not only how
2011 with funding from the Federal Aviation
much light is produced but also its spatial
Administration (FAA) Visual Guidance
relative change in photometric characteristics
distribution and its colour. In combination,
Program to gather initial data on light output
as a function of LED operating temperature.
these criteria could be used as the basis for a
depreciation, colour shift, and intensity
During the test, each luminaire was installed
functional definition of airfield luminaire life.
distribution changes from a limited number
in a customised test chamber designed to
a 30 per cent drop in light output may be
temperature of operation. The samples tested
The study was designed to observe the
operate the luminaire continuously with a
LEDs and human factors
Dr John D. Bullough, Senior Scientist at the Lighting
Research Centre, Rensselaer Polytechnic Institute
nominal 6.6A current and at a predeter-
mined temperature. The selected test LED
board temperatures were nominally 55°C,
80°C, and 100°C and were kept constant for the
duration of the test. Each chamber included
the required heating elements, controls, and
sensing probes to monitor the performance
of the luminaire. Before the beginning of the
In addition to the durability, long operating
as the flashing light. Effective intensity
life and energy efficiency of LEDs, they also
predicts the relative visibility of single-pulse
have several human factors advantages,
flashing signals well 2 , but the FAA’s current
which the Lighting Research Centre has been
definition of effective intensity for
investigating in cooperation with the FAA:
multiple-pulse flashes overestimates their
■ Wide range of correlated colour
effectiveness when the light pulses are
temperature (CCT) for white light, and
longer than those produced by xenon
more saturated colour than
strobes 3 . A definition used by ICAO better
incandescent signal lights
predicts the visibility of multiple-pulse
Instantaneous rise and decay times.
flashes, placing LEDs and other sources on
■ the same technology-neutral playing field.
The LRC’s research on aviation
With regard to the colour characteristics
of LEDs, the ability to create white light
lighting and LEDs can be found online at:
with higher CCT results in more accurate
www.lrc.rpi.edu/programs/solidstate identification of white signal lights.
illumination that is regularly confused with
colour-deficient observers 1 .
consisting of several short pulses often
appearing as a single flash, similar to signals
using xenon strobes. FAA specifies the
performance of flashing lights in terms of
‘effective intensity’, defined as the intensity
of a steady light with the same visibility
hours using a photometrically calibrated
photosensor. To monitor the changes in the
colour of the light, the spectral power
distribution was measured at least once every
1,000 hours. Figure 1 (page 39) shows a picture
of the overall set-up including the six testing
chambers and the data logging equipment.
What were the results of
the long-term test?
driving circuit. These failures happened at
2. Bullough JD, Skinner NP. 2013. Conspicuity of flashes
of light: Interactions between intensity and duration.
Journal of Modern Optics 60: 1193-1199.
3. Bullough JD, Skinner NP, Taranta RT. 2013.
Characterising the effective intensity of multiple-
pulse flashing signal lights. Lighting Research and
Technology 45: 377-390.
560 hours of operation (100°C condition) and at
3,360 hours of operation (80°C condition) for
two of the L-850B samples, and at 7,630 hours
of operation (100°C condition) for one L-850A
sample. These results help make the point that
luminaire reliability involves much more than
just LED light output depreciation.
identifier lights (REILs) and obstruction lights,
allows the use of multiple-pulse light flashes
of each luminaire was monitored every four
operate as a consequence of failures in the LED
Bullough JD, Skinner NP, Bierman A, Milburn NJ,
Taranta RT, Narendran N, Gallagher DW. 2012.
Nonincandescent Source Aviation Signal Light Colors,
DOT/FAA/TC-TN12/61. Washington: FAA.
For flashing signals like runway end
the ability to switch LEDs on and off rapidly
the end of the study. The relative light output
1. of LED colour is beneficial for correct
identification, for both colour-normal and
and kept as a reference to check against at
References yellow light. For coloured signal lights, LRC
research has also shown that the saturation
was captured using a bar goniophotometer
Of the six samples under test, three ceased to
Incandescent signals, especially when
dimmed to lower intensity steps, produce
test, the intensity distribution of each luminaire
John D. Bullough is a Senior
Research Scientist and Adjunct
Assistant Professor at the
Lighting Research Center,
Rensselaer Polytechnic Insti-
tute, where he coordinates
the Center’s Transportation
Lighting and Safety Program.
He is a Fellow of the Illuminating Engineering
Society and is the author of more than 300
publications on lighting and vision.
Figure 2 (page 39) shows the relative light
output of the rest of the samples that were
operational for the totality of the test. For one
type of luminaire, L-850A, even at the lowest
operating temperature (59°C) the estimated
time to reach an L70 value was between 9,000
hours (for the white side) and 14,000 hours
(for the red side). On the other hand, the L-850B
sample tested at the lowest temperature only
40 Volume 18 · Issue 2 · 2014 www.internationalairportreview.com