Researchers from the “Sommeil, attention
et neuropsychiatrie” laboratory (CNRS / Université Bordeaux Segalen)
and their Swedish colleagues have recently demonstrated that
constant exposure to blue light is as effective as coffee at
improving night drivers' alertness.
Based on tests conducted in real driving
conditions, the results have been published in the journal PLoS One.
They could pave the way for the development of an electronic
anti-sleep system to be built into vehicles. Before then, the
scientists will be testing this equipment in a broader range of
When driving at night, drowsiness
brought about by sleep deprivation reduces a driver's alertness,
reflexes and visual perception. Sleepiness is responsible for one
third of fatalities on motorways. Apart from taking a nap, which is
often impractical, drinking coffee remains the best preventive
measure. However, this forces drivers to stop, which they often
leave too late. For road safety purposes, it is therefore essential
to develop an “embedded” anti-sleepiness device working
Blue light is known to increase
alertness by stimulating retinal ganglion cells: specialized nerve
cells present on the retina, a membrane located at the back of the
eye. These cells are connected to the areas of the brain controlling
alertness. Stimulating these cells with blue light stops the
secretion of melatonin, the hormone that reduces alertness at night.
The positive effect of blue light on night-time alertness has been
known since 2005, notably through American research. But these
previous studies only demonstrated this effect during simple
cognitive tasks, like pushing a button in response to a light
stimulus. Driving is a much more complex task.
To study the efficiency of blue light
during night driving, a special LED lamp continuously emitting blue
light was installed on the dashboard of an experimental vehicle. The
researchers then asked 48 male volunteers, aged between 20 and 50
years, to drive 400 km on a motorway. Each driver completed three
night drives, spaced out by at least a week, between 1 a.m. and 5:15
a.m., with a 15-minute break halfway through the journey.
During each of the three nights, the volunteers were either exposed
to continuous blue light, or given two cups of coffee (one before
departure and one during the break). These either contained 200 mg
of caffeine or were decaffeinated, representing a placebo.
It is worth noting that drivers' sleep was not affected following
the journeys with exposure to blue light.
The researchers then analyzed the number of times that a driver
encroached on road markings (hard shoulder or centre line),
reflecting a decrease in alertness.
The results of this test showed that on
average, the line was accidentally crossed 15 times by the drivers
exposed to blue light, 13 times by those who had had coffee and 26
times by those who had had the placebo. Continuous exposure to blue
light while driving therefore appears to be as efficient as coffee
for fighting sleepiness at the wheel, as long as this light does not
hinder the driver. In fact, eight of the 48 volunteers (17%) found
that they were dazzled by the blue light and therefore could not do
The researchers are now verifying these
first results by making a test on a larger number of subjects,
including women and the elderly. One of the applications could be
the development of an embedded anti-sleepiness device in vehicles.
Blue light characteristics: wavelength
468nm, brightness 225 µw/cm2.
For more information
In-Car Nocturnal Blue Light Exposure Improves Motorway Driving: A
Randomized Controlled Trial.
Jacques Taillard, Aurore Capelli, Patricia Sagaspe, Anna Anund,
Torbjorn Akerstedt, Pierre Philip. PLoS One, 19 October 2012.