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NORDIC LIGHT & COLOUR
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The highest elevation angle of the sun during the shortest day
of the year, 21st of December, is only 3,35°. In the period from
the 21st of December to the beginning of February the elevation
angle of the sun will never reach 10°, this occurs first on the
3rd of February. After this day the number of hours when the
sun is over 10° increases rapidly on a daily basis, but we have
to wait until the 30th of March to observe the sun reaching the
30° elevation angle.
The highest position of the sun in Trondheim is 50,01°. There
are only four days during the year, 19th, 20th, 21st and 22nd of
June, when the elevation angle of the sun is higher than 50°; at
21st of June it lasts for 12 minutes.
The results are striking: the percentage of time when the sun is
between 0° and 10° is 35%. This means that for more than 1/3
of the whole daytime during the year we may expect a nearly
horizontal light from the sun. The time when the sun is in the
0°-10° angle interval is actually much longer than the time
when it is over 30° (26%).
Twilight
Since the sun stays for that long time just over the horizon, it
may also stay for a long time just beneath the horizon. To ex-
amine this, the twilight time was calculated! The twilight is de-
fined as a condition where the sun is no more than 6° beneath
the horizon. The total twilight duration, 430 h for ½ year, i.e. 860
h a year, is a long time. Twilight makes 19% of the night-time
during the year (the length of the daytime and the night-time
in a year is equal). The twilight duration is longest during the
summer months. During the four weeks period closest to the
summer solstice (21st of June) the twilight is strong enough to
illuminate landscape and people quite well, even daytime ac-
tivities, such as reading, are still possible without artificial light
on a clear night. There is no really dark time during the whole
night; the white night is a fact.
White nights should not be mixed up with midnight sun that oc-
curs only at places north of the Arctic Circle 66° 33’ 44’’N. The
midnight sun does not occur in the capitals of Nordic countries
and other settled areas situated about 60° N.
Duration of sunny skies
We should not forget that availability of sunlight is also strongly
dependent on the cloud cover. Let us look at the frequency of
sunny skies. For this purpose four maps were generated with
the help of the Satel-Light (Satel-Light 2013), see figure 8 and
9.
The frequency of “sunny skies” during the year in Europe north
of the Alps is rather low (30-40%), the British Islands receive
the least sunlight. In the Nordic region covered by the satel-
lite and shown on the map, the highest frequencies of sunny
skies may be found at the Baltic See (40-45%), the lowest in the
Norwegian mountains (20-25%), see figure 8. A large differ-
ence may be observed between different seasons and different
months of the year. Generally, the highest frequency of sunny
skies occurs in the spring, the lowest in the winter, figure 9.
Special features of daylight in Nordic region
The analysis made so far shows the typical features of daylight
in the Nordic countries:
1. Dominating low solar elevation angle during the year
2. Long periods of twilight and white nights in the time period
close to summer solstice, midnight sun at places north of the
Arctic Circle
3. Rather low frequency of sunny skies during the year, espe-
cially during winter
What are the consequences of the dominating low solar eleva-
tion and low occurrence of sunny skies?
When solar elevation angle is low, the sunlight accessibility is
obviously low as well, in buildings and outside, especially in
mountain regions and areas with undulating terrain.
Even if the sunlight is present, it has much lower luminous flux
than in southernmost regions, it is not perceived as dangerous-
ly strong, both for the people and for the natural environment.
The modelling of terrain and objects is sparse and gentle.
The low position of the sun contributes to frequent occurrence
of solar glare, i.e. an experience of the presence of the sun in
the visual field of a subject.
The low sun is even more annoying than a high sun, since the
direction of view is very often horizontal, at least outdoors.
People living in Nordic region are annoyed by solar glare quite
often; they have worked out an intuitive, unconscious method
for dealing with the solar glare, e.g. by turning the body and/or
visual object to a more comfortable position. Also simple sun
shading methods have been developed for usage in buildings,
Table 2. The time duration in hours when the sun is in the three elevation
angle intervals, calculated monthly for the first part of the year in Trond-
heim.