Light Pollution
Good practice
Good lighting management policies provide economic advantages as new technologies are adopted while at the same time protecting vulnerable species in the environment and mitigating the health effects of light at night on constituents. This will also make for a more attractive and appealing place for people to live and work in.
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The IES (Illuminating Engineers Society) and the IDA (International Dark Sky Association) recommend the following five principles that can and should be adopted when formulating specific policies for our region:
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USEFUL: All light should have a clear purpose. Before installing or replacing a light, determine if light is needed. Consider how the use of light will impact the area, including wildlife and the environment. Consider using reflective paints or self-luminous markers for signs, curbs and steps to reduce the need for permanently installed outdoor lighting.
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TARGETED: Light should be directed only to where needed. Use shielding and careful aiming to target the direction of the light beam so that it points downward and does not spill beyond where it is required.
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LOW LIGHT LEVELS: Light should be no brighter than necessary. Use the lowest light level required. Be mindful of surface conditions as some surfaces may reflect more light into the night sky than intended.
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CONTROLLED: Light should be used only when it is useful. Use controls such as timers or motion detectors to ensure that light is available when it is needed, dimmed when possible, and turned off when not needed.
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COLOUR: Use warmer colour lights where possible. Limit the amount of shorter wavelength (blue-violet) light to the least amount needed.
Shielding
When lighting is necessary, it is important that the luminaire is shielded so that the light is directed downwards. Any upward directed light contributes disproportionately to light pollution, and fails to provide any real and tangible benefit - it is simply wasted energy.
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Unshielded lights radiate light in all directions (see the diagram). Some lights have a cap that stops light from going straight up, but light is often able to be directed up at an angle, and these are barely better than unshielded lights. "Fully shielded" lights prevent light from being projected above a horizontal line through the fitting. This design of light is much better, but it still produces a lot of glare for people in the community, because if you are below the height of the luminaire (as is usually the case, for instance with street lights) the light can project into your eyes even when you are some distance away from the light fixture.
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The best light fixtures have cut-off shielding that directs light down towards the ground in the immediate area where the lighting is needed. This prevents spill into other areas that the light cannot be expected to illuminate, and provides the best efficiency for the energy spent on night-time illumination.
Image by Lucía García @shedka for citiesatnight.org