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See you over there!
As every gardener knows, outdoor chrysanthemums usually bloom in autumn
with short daylight hours. This is the photoperiodic effect. Pot
chrysanthemums are now sold which are either treated chemically or kept
with less daylight than is available naturally. Some wild plants respond to
photoperiodicism e.g. Yellow toadflax flowers only when the nights are
lengthening and there is uninterrupted darkness. Uninterrupted darkness is an
important factor controlling bud dormancy, flowering and leaf-fall in native
deciduous trees. Many weeds e.g. Chickweed and Dandelion seem
unaffected and flower anytime that the weather is warm enough.
Common sense tells us that animals, particularly humans, have sounder sleep
in darkness. The light sensitive cells in the retina of the eyes have to
‘regenerate’ during sleep in darkness. The nocturnal animals, particularly
small mammals, have eyes adapted to low light conditions. In the same way
that a human is rendered temporarily or permanently blind by a search light
beam, small mammals are blinded by bright lights at night. Even if this is only
partial, they are at risk from predators until their sight returns and they cannot
see to forage for food and may die of exhaustion.
Invertebrate animals are also at risk from artificial light at night.
· Electric light can affect the behaviour or nocturnal insects e.g. the
Robinson Brothers (1950) showed that a high general level of
illumination causes night-flying insects to settle as they would normally
do at daybreak so feeding, breeding and egg-laying activities cease.
The congregation of moths round bright lights provides a concentrated
source of food for some bat species at night and for birds in the early
· Increase of lighting may lead to fragmentation of habitats, producing
small isolated insect colonies. This may then affect the interbreeding
potential between the populations.
· Artificial light can affect mating of moths in other ways:
a) females do not produce the sex pheromores to attract males.
b) moth larvae do not produce overwintering pupae and so will be killed
by frost or, if they emerge as adults, die of starvation as a result of nonavailability
· Less work has been done on the impact of artificial lighting on other
insects but Bratton (1990) suggests that mayfly life cycles may be
disrupted and Crowson (1981) considers that the survival of the glowworm
is threatened by outdoor lighting.
· There is considerable evidence from experimental laboratory work that
the life cycle and development of camouflage in insects can be
severely affected by an incorrect day length.
· For birds in Britain, day length initiates behaviour patterns such as
courtship, mating rituals, reproductive cycles, migration, fat deposition
and moulting. Rawson (1923) demonstrated a close correlation
between the commencement of dawn singing in Thrushes and a critical
light intensity at sunrise. This clearly indicates the precise nature of the
control of behaviour in birds by light which artificial outdoor lighting
· Lock (1965) noted that Robins and Blackbirds began laying one or two
weeks earlier in urban gardens than in woods which could be the effect
of artificial lighting. Problems of food supply for the young may occur if
hatching is too early.
· Isolated artificial light sources on moonless nights can affect the
orientational / migrational ability of birds but this is not observed on
· Nocturnal birds are likely to be disturbed by the presence of bright
illumination. Barn Owls, Long-eared Owls and Nightjars are already
under threat and their ability to catch prey may be affected by artificial
· Birds which are normally active during the day may extend their
feeding day leading to a decrease in prey population.
· Nocturnal mammals are likely to be disturbed by the presence of bright
illumination and could be deterred from using established foraging and
breeding areas, e.g. Badgers and Otters.
· Bats – there are beneficial effects for fast flying bat species feeding on
insects attracted to artificial light sources but slower flying species are
not so attracted and these include most of those bats considered
vulnerable in Europe.
· Beasley and Zucker (1984) suggest that, in at least one species of Bat,
day length influences the male reproductive cycle and the level and
timing of peak body weight through autumn fat deposition.
· Physiological and hormonal changes initiating hibernating in Bats and
Dormice have been linked to day length.
Suggestions for limiting harmful effects of artificial lighting on wildlife
If floodlighting of buildings is to be undertaken, care should be taken to
establish the intensity of illumination being fitted and the wavelength of light
being used. Some more mellow light from which blue and ultra-violet rays are
excluded may be quite adequate – or even preferable. Ultra-violet light is very
damaging to unprotected living organisms and kills many invertebrate animals
and microscopic plant life.
The light should be directed at the buildings and wherever possible trees
should not be directly illuminated.
If security lighting is necessary, take advice and try to install lamps which
avoid the harmful effects of the blue / ultra-violet and the red / infra-red ends
of the spectrum.
These are just a few of the possible effects of artificial outdoor lighting and
increase of day length on the natural world. All the living organisms in one
environment interact so even if just one organism is affected then this could
have other ‘knock-on’ effects in the food chain.
Outen, Alan R. The Possible Ecological Implications of Artificial Lighting.
Hertfordshire Environmental Records Centre 1992.
Bratton, J. H. A Review of the Scarcer Ephemeroptera and Plecoptera of
Great Britain. Research and Survey in Nature Conservation NCC 1990.
Crowson, R. A. The Biology of Coleoptera. New York Press 1981.
Rawson, H. E. A. Bird’s Song in Relation to Light. Trans. Herts Natural
History Society 17 1932.
Lack, D. The Life of the Robin. 4th Edition Collins 1965.
Beasley and Zucker. Photoperiod Influences on the Annual Cycle of the
Male Pallid Bat (Antrozous pallidus). J Reprod, Fert 70 1984.
Interesting images of the Earth at night as seen from space:
So what steps can businesses take to reduce the amount of energy used for lighting? Here’s a few simple suggestions: