Sky
glow (light pollution) arises from a combination of artificial lights
emitted directly into the sky from light fittings, and from light reflected
up into the sky from buildings and the ground. Hence, the Campaign for Dark
Skies currently recommends that:
1.
Lights should be installed in full cut-off housings, to prevent light
being emitted above the horizontal.
2.
Although astronomers prefer the light emitted by low pressure sodium
lamps (as this can be filtered out), high pressure sodium lamps are
acceptable provided no light is emitted above the horizontal.
3.
'Over-lighting' must be avoided. Using only the correct amount of
light for the task in hand, according to accepted standards, will reduce the
amount of reflected light contributing to sky glow.
4.
Unnecessary night-time lighting, particularly decorative
flood-lighting, advertising lighting and sports floodlighting, should be
switched off at 11pm or midnight to reduce overnight pollution.