Scotobiology – The Biology of Darkness
Tony Bidwell and Peter Goering
The development of
plants, particularly those in temperate zones varies with season and
most plants detect season by the duration of darkness. Hence “short-day
plants” require long nights, and “long day plants” require short nights.
Short-day plants normally bloom in the autumn when the days are shorter.
Long nights initiate the onset of flowering, and later, as nights
lengthen, the onset of dormancy, which enables plants to withstand the
vigours of winter. If short-day/long-night plants are illuminated even
briefly during a long night, they detect this as two short “nights”,
under continuous night-time light pollution plants respond as if there
were no night. In either case flowering and development are compromised.
The effects of successive nightly illumination are cumulative, flowering
and dormancy – and hence survival – of short day-plants
Birds suffer huge
losses due to light pollution. There has been a tremendous increase in
the number of brightly illuminated tall infrastructure, including
buildings, power plants, chimneys, telecommunication towers and wind
generators. Birds are disoriented by bright lights, and either fly
toward them or are unable to see structures behind them. The behaviour
of many animals, including mammals, amphibious and insects can be
seriously affected by light pollution.
The effects of
light pollution are also considerable at the community and ecosystem
level. Disturbance of plant and animal life-cycles within a community
affects the survival of otherwise unaffected members. Light pollution
from cities and highways is sufficiently widespread to affect very large
areas, and the effects on individual organisms can disrupt the
population balance and thus the integrity of whole communities.
Human health is
more severely affected by light pollution than is generally realized.
Human hormone regulation, physiology and behaviour have evolved in a
diurnal pattern of night and day. The normal operation of sleep/wake
cycles, hormone cycles, the immune system and other biochemical
behaviour, depends on the daily alternation of light and dark. For
example the immune system functions more strongly during the day to
protect the body against invasion, while antibody production is highest
at daytime. At night, the killer cells that attack tumour and establish
invasion are more active. Night-time light pollution imbalances the
different activities of the immune systems, to the serious detriment of
health, and disrupts circadian hormone cycles with resulting emotional,
physical and psychological change.
may become a major ecological and human health issue if we continue to
ignore the evidence of its increasing impacts. A hopeful aspect of the
problem is that much light pollution is unnecessary and could be easily
controlled. The lights on high structures to prevent airplane collisions
are of course essential, but their effects may be ameliorated by using
specific wavelengths or flashing lights. The light pollution from
internal illumination of large buildings could be reduced by curtains
and floodlighting of buildings and statues could be dramatically
A major reduction
of light pollution can be achieved with shaded/focused street, highway
area and advertising lightings; less powerful, downward-focussed street
can provide adequate lighting without skyward pollution. Finally,
reducing light pollution would also lower the environment impacts
associated with electricity generation.
More work in the
science of scotobiology needed to understand the impacts of light
pollution, and to promote practical solutions.
is at the Queen’s University, Wallace, Canada (E-mail:
is at Muskoka Heritage Foundation Toronto, Canada (E-mail: [email protected])
article is condensed from ‘Global Change Newsletter’ published by IGBP
Secretariat, Stockholm, Sweden.)