Veiling glare in car windshields

Abstract: Veiling glare is the phenomenon when the dashboard or parts of the dashboard
reflects into the windshield and creates veiling images. These images are
both disturbing and impair the driver’s vision of the road scene. Cars are
today more and more designed to have a "dynamic" expression with further
raked windshields and the designers also wants to have the possibility to
use lighter colors in the interior. This can lead to unwanted consequences
in the form of an increased amount of reflections from the dashboard into
the windshield.
The goal with this thesis was to describe a measurable requirement that
correlates with customer expectations together with different positions and
angles of the light source, windshield and dashboard, material attributes of
the dashboard and windshield characteristics like anti-reflective coating.
The thesis work was carried out at the department of Human Factors
Engineering and Ergonomics at Volvo Car Corporation, Gothenburg.
There is an existing requirement that restrict the gloss and lightness of
the instrument panel top surface. This requirement is valid at the specular
sun angle (geometric relationship which creates a direct reflection from the
light source into the driver’s eyes), which gives the gloss a much larger
effect in the requirement compared to lightness. Volvo Cars has realized
through own observations, that instrument top panel lightness plays an
important role in the experience of veiling glare, particularly at high sun
angles. Therefore Volvo Cars has created a complementing requirement that
express a maximum lightness value based on a linear relationship tied to the
windscreen angle. The problem is that it doesn't exist any linear
relationships when the phenomenon veiling glare is examined further.
In a laboratory environment a measuring method was developed to research the
affecting factors of veiling glare at high sun angles. This work has been
done through the use of several quality tools as Design of Experiment and
Binary Logistic Regression. A subjective survey was performed to determine
the customer acceptance for veiling glare at for different road scenes. The
result from these studies was then combined to express maximum lightness
value tied to geometrical properties between the windshield and the
dashboard.