Last edited 02 Sep 2020

Light pollution

Light pollution is a term that usually refers to outdoor artificial light that is considered excessive or obtrusive, described by the Campaign for Dark Skies as ‘artificial light which shines where it is neither wanted, nor needed’.

According to the Campaign to Protect Rural England (CPRE) only one tenth of the English countryside has a truly dark night sky, and stars are becoming much more difficult to see because of ‘sky glow’ which can be visible for up to 50 miles.

Light pollution has the potential to disrupt breeding patterns of nocturnal animals, insects and the migration of birds. It can also have an adverse impact on the health and wellbeing of people, disrupting natural body cycles regulated by darkness and light. Light after dusk, when people are attempting to sleep, can trigger daytime physiology, telling the brain to become more alert, increasing the heart rate and body temperature, and suppressing the production of melatonin. It is thought that sleep disorders, increased stress and certain types of cancer can be developed if sleep is disturbed by artificial lighting.

It can be a sign of inefficient lighting that is costly, wasteful, a nuisance and generates unnecessary carbon emissions.

The main categories of light pollution are:

Glare: A discomforting or disabling brightness which causes a loss in visibility as stray light scatters within the eyes. An example would be driving on a road and being temporarily blinded by oncoming headlights. Sensitivity to glare can vary widely.
Sky glow: This occurs from both natural and man-made sources of lighting which increase night sky brightness. Light can be emitted directly or reflected into the atmosphere to produce a luminous background. The ability to view the stars at night is hindered.
Light trespass: Where light spills into areas in which it is unwanted. An example of this would be the light from an exterior street light entering a bedroom window and illuminating the interior.
Light clutter: An area where there are large group of lights that may cause distraction or confusion. Clutter can be found in particular in parts of cities or on busy roads.
Over-illumination: The excessive use of lights.

The first UK law aimed at controlling light pollution came into effect in 2006 under section 102 of the Clean Neighbourhoods and Environment Act. This places light alongside noise and smells as a potential statutory nuisance and permits local authorities to take action against 'exterior light emitted from premises so as to be prejudicial to health or a nuisance'.

Most commonly, problems are caused by poorly directed of unshielded security lighting and street lighting. Light pollution can be reduced by only using artificial lights when and where they are required. Some local councils turn street lights off between midnight and 5am, and outdoor lights can often be dimmed to reduce their impact. The CPRE suggest that councils spend around £616 million per year on street lighting. This can account for 30% of their carbon emissions.

CPRE has called for local authorities to:

Preserve dark skies by having a presumption against new lighting in existing dark areas.
Allocate lighting zones to help determine where street lights should and should not go.
Prevent inappropriate and badly designed lighting of development that masks views of the night sky.

The Campaign for Dark Skies (CfDS) aims to ‘…preserve and restore the beauty of the night sky by campaigning against excessive, inefficient and irresponsible lighting that shines where it is not wanted nor needed’. It suggests that approximately £1bn per annum is wasted by inefficient lighting in the UK alone.

CfDS suggests that:

Street lighting should be full cut-off lighting, preventing light being wasted into the sky, and that it should be shielded to prevent spilling into neighbouring properties, dimmed overnight and should not incorporate reflectors.
Home and business floodlighting should not be used, but if it is unavoidable, should shine downwards, and only where required.
Businesses should avoid unshielded bulkhead lighting and shielded bulkhead lighting should only shine where it Is needed.

Light pollution can be a particular problem on construction sites, where new or temporary lighting may be installed and large areas flood lit. PPG6, Pollution Prevention Guidelines, suggests that construction light nuisance can be reduced by 'screening, effective programming of work, directional lighting and type of lights used'.

In June 2016, CPRE launched the most detailed ever satellite maps of England’s dark skies. The interactive maps were produced with satellite images captured at 1.30 am throughout September 2015. The brightest spot is above a Tata Steel foundry in Rotherham, whilst the darkest is a secluded hillside on the East Kielder Moors in Northumberland. Just 22% of England is untouched by light pollution.

NB: According to BRE’s The essential guide to retail lighting: Light pollution '... can also take the form of unwanted spill light to neighbouring properties and gardens.'