University of Kent
Uploaded to Knowledge Centre
8 September 2021
The aim of this research project was to evaluate the effectiveness of existing vehicle brake light designs, in particular comparing conventional bulb and more recent LED based brake lights.
The research has provided a more detailed method for evaluating brake light efficacy, accounting both for reaction times or the time between brake light activation and braking, and cognitive perception times based on brain responses evoked by different brake lights.
The report says the strong statistical difference between LED and bulb-based brake lights for every tested participant, in terms of both timing and cognitive responses, shows that LED based brake lights have a clear advantage in their effectiveness to draw a quicker response from participants – and as such recommends that bulb-based brake lights should be phased out.
Over half of all road collisions are caused by either lack of driver attention or insufficient gap between vehicles, with collision from the rear being the most common cause in the UK. Yet these collisions should be among the most avoidable since brake lights are designed to clearly indicate to a following driver that a vehicle is slowing down or stopping.
Brake lamps historically used incandescent bulbs, but LEDs are attractive to manufacturers and are becoming increasingly common. Vehicles are increasingly being fitted with unusual and interesting shapes and patterns for their brake lamps.
However, very little research has been conducted to date on assessing the effectiveness of brake light design, and almost none has considered the effect on brain perception. Since a brake light must be noticed before it can be acted upon, and with so many collisions caused by inattention, the perception of new light designs is an important and timely study, which this research has addressed.
The aim of this research project was to evaluate the effectiveness of existing vehicle brake light designs, in particular comparing conventional bulb and recent LED based brake lights.
The experimental study required electroencephalogram (EEG) data collection, time stamps for brake light turning on events, and time stamps for brake pedal press events.
To meet these requirements, the project team developed a custom hardware platform with multiple event marker generation, using a 32-bit microcontroller. A driving environment was simulated using a video projected behind the brake lights. For the simulation of brake lights, 10 different brake lights were fitted (two from conventional bulb and eight from LED) on two adjustable stands to model the actual horizontal distances in cars. EEG data was measured from channel Pz (an area of brain which is known to be involved in decision making).
Each session was designed as a simulated driving paradigm with the brake light assembly in front of the participant representing a leading vehicle. Those brake lights were activated at random intervals. Subjects were instructed to continuously depress the accelerator pedal until they perceived an activation of the brake light in the simulated leading vehicle. At that point they were told to immediately release the accelerator and depress the brake pedal.
Data was recorded from a total of 22 volunteers. All possessed valid UK driving licenses and had normal or corrected-to-normal vision. Half of the subjects were classed as experienced drivers, with more than four years’ driving experience. Ethics approval for all experiments was obtained from the Faculty of Science Research Ethics Committee at the University of Kent.
The first data analysis was based on reaction time latencies evoked by the different brake lights, while the second data analysis was based on brain responses (known as P3) evoked by the different brake lights simulation.
Results indicate that versions of brake lights containing incandescent bulbs were slower than all the eight LED lights (and this result was statistically significant).
It is known that bulbs take longer to light up than LED lights (for example, there is usually no discernible light output until up to about 50 ms, after power is applied) but the cognitive reaction time delay was about 170 ms when comparing a bulb and its LED equivalent, which shows that LEDs have the ability to evoke brain responses more quickly. The age of participants did not make any difference to reaction times, but driving experience mattered.
A unique approach for the timing analysis was used to identify the cognitive response after seeing the brake light and lifting the foot from the accelerator, which assisted in understanding the influence of the cognitive action component of raising the accelerator pedal after seeing the brake light. This analysis showed that at the slow end of the reaction time, inexperienced participants were especially slow.
Given that the hazard perception test is now included for learner drivers, it is recommended to increase the amount of training in this regard to enable quicker cognitive perception.
In conclusion, although the subject pool was small and real-road traffic conditions were not tested, the strong statistical difference between LED and bulb based brake lights for every tested participant with both timing and cognitive responses, show that LED based brake lights have a clear advantage in their effectiveness to draw a quicker response from participants and as such the report recommends that bulb-based brake lights should be phased out.
Find out more and download the full project report from the Road Safety Trust website: