This project was conducted by the Lighting Research Center at Rensselaer Polytechnic Institute (www.lrc.rpi.edu) under FAA contract FAA/05‐C‐AT‐

RPI.  This summary was prepared by the Lighting Research Center on behalf of the FAA.

Further details: Don Gallagher, donald.gallagher@faa.gov;  http://www.lrc.rpi.edu/programs/solidstate/aviation.asp.

The model is specified by the equation:

                  B/L = 2.32DvSrf + 1.09

In this equation, Dv represents the chromaticity

difference between the incandescent and LED

lights, Sr represents the relative saturation of the

LEDʹs dominant wavelength, and f represents how

closely the LEDʹs chromaticity is to that of its

dominant wavelength.

Federal Aviation Administration 

Research Highlights 

Study Goals

Light‐emitting diodes

(LEDs) are being

used more frequently

for airfield lighting.

LEDs differ from

incandescent lights in

color saturation and

correlated color

temperature, and LED airfield lights can appear brighter

than incandescent lights of the same nominal color and

luminous intensity. These differences can be distracting

to pilots, and some have questioned whether LED

airfield lights are too bright. The goal of this study was

to develop a model that could be used to quantify the

brightness perception for blue, white, and green LED

signal lights relative to incandescent lights.

Research Activities

The LRC conducted human factors experiments

comparing LED and incandescent signal lights. Subjects

viewed LED and incandescent lights varying in intensity

and judged which appeared brighter. The results

confirmed that LED signal lights are perceived as

brighter than incandescent signal lights at matched

luminous intensities. Brightness relationships were

unaffected by signal light intensity, background light

level, or the number of signal lights viewed.

   Previously published models of brightness appearance

did not accurately predict the brightness differences.

Therefore, the LRC developed and validated a new

model that could be used to predict the brightness‐to‐

luminous‐intensity ratio (B/L) for FAA blue, white, and

green LED signal light colors relative to incandescent.

B/L values for typical LEDs ranged from 1.4 to 1.6.

    The LRCʹs brightness prediction model for blue,

white, and green LED aviation signals was published in

an FAA Technical Note and incorporated into FAA

Engineering Brief 67, Light Sources Other Than

Incandescent and Xenon for Airport and Obstruction

Lighting. Following several complaints about the

brightness of LED lights at Raleigh‐Durham

International Airport (RDU) installed prior to the model

development, FAA engineers adjusted the LEDsʹ 

intensity according to the model and no further

complaints were received.

Chromaticity regions of equal brightness/luminous intensity

(B/L) values for blue, white and green signal lights.

For More Information

 http://www.airporttech.tc.faa.gov/DesktopModules/FlexNews/Dow

nloadHandler.ashx?id=467430e5‐d2dd‐44e2‐9f15‐

1910a4825830&f=TC‐TN15‐32.pdf

 http://www.airporttech.tc.faa.gov/DesktopModules/FlexNews/Dow

nloadHandler.ashx?id=4b709f63‐94f3‐4643‐887b‐

259004c431c1&f=S10103‐Bullough.pdf

 http://cormusa.org/uploads/2016_Federal_Aviation_Administration

_Lighting_Research_and_Development‐

Donald_Gallagher__Federal_Aviation_Admini.pdf

Predicting LED 

Signal Brightness