SAE Study: The Effects of Emergency Light Colors and Intensity

SAE in 2008 realized that the “increased use of LED light sources made it more important to understand color and intensity.”  They devised a study,  Effects of Warning Lamp Colors and Intensity on Driver Vision because the agency knew that the use of particular color in emergency vehicle lighting were based on strong and varied traditions.  As the LED industry rapidly advanced, SAE wanted to know which color light had the most and least impact on motorists of varying ages during the day and the night.

Unfortunately, only 8 people participated in this study, 4 between the ages of 18-28 and 4 between the ages of 62-79. All were licensed drivers with good vision and were not colorblind. Each participant performed 3 tasks: to search for emergency warning lamps, to look for a first responder in front of a vehicle while lights were flashing, and to rate the conspicuity of each emergency lamp color.  Each sat in a stationary vehicle in an open paved area while performing the operations.

The SAE Data Pool is too small to draw conclusions about Warning Light Colors

The study concluded that it was more difficult to see flashing warning lights during the day, but locating first responders was harder at night, results which are not surprising.  It also determined that the color BLUE was the most conspicuous both day and night, but a higher flash intensity was needed at night for the color. This is somewhat contradictory to the Illinois study as presented later in this report, but the tasks, conditions, arrangement of lights, the sample section, and the goals of the studies were not the same in each case.  One drawback when comparing various studies is that they do not measure the same aspect of color under the same conditions, so promoting one color over another would be a difficult task based solely on these findings.

SAE’s suggestions for future research are as follows: to better define the term “effective” intensity of flashing lamps, to establish the connection between subjective conspicuity of most studies and objective search performance,  to develop and validate common search tasks in order to better evaluate and compare findings, and to gather relevant data on color effects in daytime and nighttime.

SAE states:  “we do not intend the present discussion to be definitive.”  This was just the beginning of the emergency warning light industry moving full-on into using LEDs.  Since that time many other studies have been devised to determine which other types (incandescent, halogen, strobe) of colored lights are best under specific conditions and most of all how they affect the cognitive perception of oncoming motorists. SAE recommends the continual gathering of information and conducting of research in order to determine once and for all what is the most effective emergency light flash pattern and color.

Further Reading