What are the three types of light pollution?

Sky Glow:  This is the brightening of the night sky which can be seen emanating in the horizon from cities and towns.  It is caused by the illumination of air molecules and particles and is created both by reflected surfaces and badly directed light.  Light that travels near the horizontal is the most damaging as it travels furthest and lowest through the atmosphere.  This can be avoided by ensuring lights are pointing down.

Glare: This is the uncomfortable brightness of a light source when viewed against a contrasting darker background.  Due to the rural and less populated character of our landscape, lights in rural areas will be relatively higher in glare than in urban areas. Many LED floodlights are tremendously strong, creating this type of effect.

Light Intrusion:  This is the trespass of light spilling beyond the property or area being lit.  Although this pollution generally relates to windows and intrusion into private property, light intrusion also applies to habitats and areas of high species interest. 

To reduce our impact on the dark skies, the following best practice principles should be followed when installing outdoor lighting.

  • Angle Lights Downward – why light the night sky above the horizontal?
  • Lamps of 500 lumens and less are appropriate for most domestic purposes.
  • Point where the light is needed not in a direction that causes a nuisance to neighbours or wildlife.
  • Switch off when not needed. Use proximity sensors.  Avoid dusk-till-dawn sensors
  • Light to the appropriate illuminance – do not over light needlessly.
  • Lamps above 500 lumens should be installed in dark sky friendly fixtures that prevent unnecessary upward light.
  • Install at the lowest possible height to achieve lighting levels.
  • Avoid bright white and cooler temperature LEDs – the temperature is measured in Kelvins. Ideally, use LEDs with a temperature of 3000 Kelvins or lower; those above this threshold produce a harsh glare and emulate daylight; studies of this bright white/blue light are suggesting these are particularly harmful to nocturnal wildlife and human eyesight.

Find out more about our project to to gain internationally recognised ‘Dark Skies Reserve’ status for the Lake District National Park and how you can get involved...


Header image: Earth Observation Group, NOAA National Geophysical Data Center. Data processed by LUC on behalf of CPRE