Newslink October 2021

Special feature: Vehicle lights
Continued from page 23
Detection, Conspicuity and DRL
Generally, the greater the contrast
between the vehicle and its background
the greater the probability it will be
detected. For light coloured cars, the
contrast is generally greater than for dark
coloured cars. But the contrast of a light
coloured car against the background
does not alter if the ambient illumination
changes. Because the visual systems’
sensitivity to contrast diminishes with
decreasing illuminance, the probability of
detection will grow smaller as the
ambient illumination drops. Even on
sunny days, the ambient illumination can
vary considerably. The driver is not only
confronted by a diversity of background
luminances caused by the background
itself, but also by more marked changes
as the background alternates between
shade and full sun. As a result, a vehicle
that should be clearly visible in direct
sunlight becomes relatively difficult to
see in dark shade.
The luminance of a light source, on the
other hand, is constant - if the source is
bright enough, its luminance will be
greater than that of unlit objects in the
surroundings.
As the ambient illumination decreases,
the contrast between the light source and
its background will actually increase.
Therefore, if a vehicle cannot be properly
detected for one reason or another, it is
always advantageous for that vehicle to
use lighting. This is particularly true
during twilight, poor weather conditions
and when the sun is very low on the
horizon, eg, sunrise and sunset. Even on
very sunny days, a car without lighting
can easily disappear into the
background, for instance, in the shade of
buildings or trees. The use of lighting can
ensure that – thanks to the heightened
contrast – a vehicle can still be easily
detected under such conditions.
Recognition, identification and
the role of expectations
The most elementary form of
perception is detecting whether
something is there. It becomes more
complicated when someone must also
indicate the category of object that
something belongs to: the recognition or
identification of objects. The terms
‘recognition’ and ‘identification’ are often
interchanged, and imply that an object is
given the right label by an observer (this
is a car). Some authors have noted that
with recognition, one is only stating that
the object concerned has been seen
before, while identification implies more
than that: the recognised object is
identified as belonging to a particular
category, eg, a car. In recognition and
identification, experience and memory
play a role. It is essential that road users
see relevant objects (in this case
implying detection). But the detection of
something is generally insufficient to
allow adequate decisions with regard to
behaviour in traffic.
This is why it is important that the
correct interpretation is given to that
which has been detected; the correct
meaning or identification must be
associated with the visual impression.
An event or action can be generated by
the surroundings, or by the observer who
is looking for a particular part of the
surroundings, or else by an interaction
between these two processes. The
distinction between the processing and
perception of physical characteristics and
the observer’s influence on this process of
perception is also indicated by the terms
for bottom-up versus top-down processes.
Various researchers have shown that
the observer himself exerts significant
influence on whether a particular object
is noticed. An observer, who expects to
encounter objects with certain physical
characteristics, will more readily see
them than when he does not expect
them. Hills emphasises the role of
expectations in traffic: Another important
factor affecting a driver’s detection and
perception of a potential hazard is his
perceptual set or his expectancies. These
are formed both from long-term experience
and by the short-term experience of the
previous few minutes driving. These can
profoundly affect the driver’s
interpretation of various visual features
and signals in a scene and also the
various visual judgments he has to make.
Conclusion
Daytime Running Lights are a relatively
new feature on most cars. Unlike
headlights, DRLs are fairly dim and don’t
illuminate the road ahead. Their purpose
is to increase the visibility of your car, so
that other drivers can see you on the
road. At night, your headlights and tail
lights are illuminated, which means that
it’s easy for other drivers to spot you.
However, during the day, most drivers
turn their lights off and it’s not as easy to
spot other vehicles quickly.
However, DRLs’ popularity and
usefulness has been debated for decades.
They are most popular in countries
further north, where there is less light
(especially in winter). It makes sense,
then, that countries such as Sweden,
Norway, Iceland, Denmark and Canada
were among the first to require DRLs on
all vehicles. In these countries, multiple
studies showed that the addition of DRLs
does reduce accidents. In other
countries, however, DRLs are not as
popular, particularly the USA. There were
similar mixed reactions in the UK.
From 2011, all new vehicles have
been required to have daytime running
lights. Although daytime running
lights are intended to make the road
safer for all drivers and pedestrians, there
are many critics who argue that they do
the opposite. The biggest concern for
many drivers is the brightness of DRLs.
Even though brightness regulations are
put in place by each country, some
groups have argued that these standards
are too high, and that some DRLs are
allowed to be as bright as headlights,
which can potentially blind other drivers.
In theory, DRLs should be dim in
comparison to your headlights, but this
isn’t always the case.
Additionally, DRLs on larger vehicles
are more likely to be placed higher up,
meaning that they could shine directly
into the eyes of other drivers. Another
argument commonly made is to do with
geographical location. A lot of DRL critics
live in the US or the UK, and they think
that they’re less necessary in countries
further north. In the US/UK, there’s more
sunlight in the day, which obviously
makes DRLs less useful.
Considering the potential safety
hazards caused by daytime running
lights, certain groups have lobbied to ban
them. In reality, there is some truth in
the idea that DRLs aren’t needed in
certain locations. Some studies have
shown that daytime running lights are
three times more effective at reducing
accidents in Nordic countries than in the
US, for example.
Still, there is no evidence to suggest
that daytime running lights are harmful
in any way.
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NEWSLINK n OCTOBER 2021