Newslink October 2021

Special feature: Vehicle lights
Daytime Running Lights have been a feature of cars for over a decade, but a general poor
understanding of their role has left some drivers in the dark. Tom Harrington explains why their
role in illuminating drivers is critical – and the factors that lead to trouble when wrongly used
DRLs and the importance
of visibility and conspicuity
The golden rules of lighting up your car
are to see and be seen. In accordance
with EC Directive 2008/89/EC,
dedicated Daytime Running Lights (DRL)
were required on all new passenger cars
and small vans from February 2011
onwards, and on all other new types of
road vehicles (including trucks and buses
but excluding motorcycles and
agricultural tractors) from August 2012.
Daytime Running Lights automatically
activate when the engine is switched on.
They are a fantastic asset to road safety
and reduce the likelihood of a side or
head-on collisions during the day.
However, just as the darkness creeps
in unnoticed so too has an over-reliance
on modern technology and the fear is
that too many rely solely on DRLs when
darkness falls during the winter months.
For a time, several US states banned
the use of these lights entirely. In the
1990s, General Motors pushed to
include DRLs on all vehicles in the US.
This was met with resistance, but
eventually government regulations
allowed their use, and their popularity
has increased ever since.
But judging from recent press
announcements, a growing number of
motorists are mistaking their DRLs for
dipped headlights. Now, no one is doing
this intentionally. It’s an honest mistake
as drivers start out in the daytime and
fail to recognise the fading light. But
unfortunately it poses a severe road
safety risk. DRLs don’t produce enough
light to illuminate the road in darkness.
Some manufacturers choose to pair front
daytime running lights with rear ones
too, but it is not compulsory. This means
there may be some motorists driving
around at night in the mistaken belief
that just because they have lights which
switch on automatically at the front; they
are also on at the rear. So, driving with
DRLs at night not only seriously
diminishes your view of the road, your
visibility to others is minimal and you
could run the risk of being rear ended.
Therefore, if you have dedicated DRLs on
your vehicle, make sure to switch to your
headlights during ‘lighting up’ hours –
legally defined as ‘the period
commencing one half-hour after sunset
on any day and expiring one half-hour
before sunrise on the next day’.
Visibility, Detection and DRL
Why is the issue of DRLs so
important? It all comes down to our
ability to see clearly, levels of visibility
and perception.
‘Visual perception’ is a concept which
refers to all perceptual processes and
results imaginable. As a result of its
generalised nature, the literature often
distinguishes between the various
aspects of perception. Concepts such as
detection, conspicuity and visibility are
often mentioned in the perception
literature. For the purposes of
clarification, therefore, some of these
concepts will now briefly be discussed.
The concepts of visibility and
detectability are often interchanged.
Visibility can be defined as a 50%
probability of detection (threshold
of visibility). If an object becomes more
visible it is generally implied that its
detection improves in one way or
another, so that the probability
of detection becomes increasingly
greater; this implies that, in general, an
object can be detected at a greater
distance, or that observers need less
time to decide whether or not an object
is present (reaction time).
Visibility is subject to a human
assessment component, as there is no
equipment that can directly measure
visibility: human intervention is always
necessary to determine this parameter.
Often, such factors are studied with the
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NEWSLINK n OCTOBER 2021