Artificial light has done much to safeguard and enhance our night time environment but, if not properly controlled, obtrusive light can present serious physiological and ecological problems.
Light pollution, whether it keeps you awake through a bedroom window or impedes your view of the night sky, is a form of pollution but without too much trouble this form of pollution can be reduced without reducing its beneficial lighting task.
Examples of light pollution are:
- sky glow
- glare which is the uncomfortable brightness of a light source when viewed against a dark background
- light trespass which is the spilling of light beyond the boundary of the property on which the source is located
These waste not just electricity and thereby large sums of money, but more importantly the planet’s finite energy resources, as it results in unnecessary emissions of greenhouse gases which should also be kept to a minimum.
How to reduce light pollution
Listed below are some easy ways to reduce the problems of unnecessary, obtrusive light:
- switch off lights when not required for safety and security It is possible to introduce the concept of a curfew with further limitations on lighting levels between agreed hours eg advertising and decorative floodlighting off between 11pm and dawn
- direct light downwards wherever possible to illuminate its target, not upwards. If there is no alternative to up-lighting, then the use of shields and baffles will help reduce spill light to a minimum
- use specifically designed lighting equipment minimises the spread of light near to, or above the horizontal
do not “over” light
- to keep glare to a minimum, ensure that the main beam angle of all lights directed towards any potential observer is kept below 70º. It should be noted that the higher the mounting height, the lower can be the main beam angle. In places with low ambient light, glare can be very obtrusive and extra care should be taken in positioning and aiming
- wherever possible use floodlights with asymmetric beams that permit the front glazing to be kept at or near parallel to the surface being lit
- for domestic and small scale security lighting, there are 2 solutions:
passive infra-red detectors can be used to good effect, if correctly aligned and installed. A 150 W (2000 lumen) tungsten halogen lamp is more than adequate. 300/500 W lamps create too much light, more glare and darker shadows
all-night lighting at low brightness, is equally acceptable. For a porch light a 9W (600 lumen) compact fluorescent lamp is more than adequate in most locations
If you are involved in the design or installation of lighting, the Institution of Lighting Engineers strongly recommends the adoption of the following obtrusive light limitations for exterior lighting installations.
Institution of Lighting Engineers light pollution leaflet