What light pollution is
Light pollution is light that does not do its job. Instead of falling where it is needed, it spills sideways and upward from fixtures with poor optics and the wrong light distribution, or that are badly aimed. It takes five main forms.
- Sky glow: the brightening of the night sky over towns and cities
- Glare: excessive brightness that makes it harder to see, especially into shadows
- Light trespass: light falling where it is not wanted, such as onto a neighbour's property
- Clutter: bright, confusing groups of lights that can distract drivers
- Energy waste: power spent on light that serves no purpose
Why it matters
Every lumen sent into the sky or onto the wrong property is energy paid for and wasted, and the electricity behind it adds to greenhouse gas emissions.
Poor lighting can also undermine the safety it was installed for. Glare reduces visibility, and bright, unshielded lights next to deep shadows make it hard to see what is happening around you.
Artificial light at night affects wildlife too. It can disorient migrating birds and disturb the natural rhythms of many nocturnal animals. And as sky glow grows, fewer stars are visible from where most people live.
Myths about brightness and safety
"The brighter, the better." In fact, the eye adapts to low light and becomes far more sensitive in it. Even, moderate lighting gives the best all-round visibility at night, while light seen directly from an exposed source spoils night vision and causes glare.
"Bright lights mean safety." Unshielded lights create harsh contrast: glare beside dark shadows, and both hide what is there. Good visibility comes from uniform light without glare, not from more light.
"All lights are the same." Fixtures that let light escape above the horizontal waste energy and cause trespass. Well-shielded fixtures reach the same light level on the ground with less power.
Myths about cost and the night sky
"Cheap lights save money." A well-designed, well-shielded luminaire puts its light on the ground and needs less power to do it. Over its life, the energy saved usually outweighs a higher purchase price.
"Nobody cares about the night sky." Communities, parks and observatories increasingly do, and many places now have bylaws that limit outdoor light. A dark sky is part of the natural environment, as worth protecting as a forest or a river.
The solutions
Light pollution is a design problem, so it has design solutions. Most of them also cut energy use.
- Replace older high-pressure sodium, metal halide and mercury vapour lamps with efficient LED luminaires
- Use good optics to aim light only where it is needed
- Choose full cutoff fixtures with zero uplight
- Light to the level the task requires, and no more
- Use controls to dim or switch off lighting late at night when areas are not in use
Where to start
Start with a photometric design. Before anything is bought, it shows how much light reaches the ground, how much spills past the property line and how much goes up. Ratings such as BUG make it easier to compare fixtures and to show that a design meets local rules.