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NORDIC LIGHT & COLOUR
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often a mixture of textiles and venetian blinds, figure 11. The
venetian blinds are used when the sun is a source of overheat-
ing or glare, the slats may be positioned to nearly completely
reject the light protecting users against the excessive radiation,
but they may also be adjusted to the cut-off position allowing
penetration of light from the ground and the low part of the sky
while just rejecting the sunlight. The textile curtains are used
when the sky is a little too bright. Many other configurations
are also possible.
The solar glare from a low sun occurs in the Nordic region
from nearly all sky directions, from the south in winter, from
the east and west in spring/autumn and even from the north-
east and north-west in the summer. It may occur at a very
different time of the day: in the middle of the day in winter, in
the morning and evening in spring/autumn. In summer it may
happen even during the night time.
When the solar elevation angle is low the effect of reflected
sunlight is much stronger, since the reflectance of specular
surfaces increases with the incidence angle of light. It is nearly
similar for water, ice and snow, figure 12. The strong effect of
reflected light may be perceived negatively (glare) or positively
(larger light flux) for daylighting of interiors.
Sometimes the daylight may enter buildings more from below
than from the sky. Such effects happen when the sunlight re-
flected from the ground makes stronger illumination than the
whole sky, which may be heavy overcast at the moment.
Additionally when the solar elevation angle is low the way of
solar radiation through the atmosphere is longer, resulting in
excessive scattering of light. Consequently, the mean colour
temperature of sunlight during the year is lower, which means
more of the yellow-red light, figure 13. Sometimes even a
purple colour may appear on the sky when the blue skylight is
mixed with the reddish sunset sunlight, figure 14.
Furthermore when the solar elevation angle is low the sun-
light direction has a very strong impact on the modelling of
landscape and buildings. The vertical surfaces, mostly building
facades, are sometimes lighted very strongly by nearly hori-
zontal sunlight from the side and appear brighter than both the
ground and the sky. Looking at the picture in figure 15 we may
ask how the buildings are illuminated. It seems like they are
self-luminous.
The low occurrence of sunny skies makes us used to the gray
sky. The gray sky is a prevailing condition; a form of reference.
It makes us aware of the high value of the solar radiation, both
for our vision and health.
The human memory of an event, as described by Daniel Kahne-
man (Kahneman 2011), is characterized by the neglecting of
time and the profound impact of the top-peak and the end of
the event. Applied to remembering daylight, it means that even
a very short appearance of the sun on the sky that creates
a nice, beautiful or a dramatic image is remembered much
better than hours with an overcast sky. We neglect the time of
grey sky with slightly variations of luminance, we remember
the top-peaks, i.e. the very special images often created by the
sunlight penetrating through the cloud cover or illuminating it
from beneath. We remember the image best in its full strength,
its most expressive variant.
Conclusions
The differences between daylight in the Nordic region and other
regions have been demonstrated. The main reason for this is
the dominating low solar elevation angle during the year and
consequently the long period of twilight, as well as the low
frequency of sunny skies.
Those geographical and climatic facts have a strong impact on
the illuminance level on the ground, at the colour of the day-
light, and on the modelling of landscape, buildings, terrain and
people. The low sun is also a serious and changeable source of
solar glare.
A series of different specific phenomena may be observed in
Nordic countries, as e.g. white nights, self-luminous objects
and heavy cloud coats.
The low frequency of sunny skies contributes to a better
remembering of various expressive images that appear on the
sky in the Nordic region as the prevailing gray sky is a neutral
reference. In comparison to it, colourful sky images or images
characterized by strong contrast appear as very interesting,
even if they only last for a moment.