The need for outdoor lighting has greatly increased for purposes of safety, commerce, and recreation. At the same time, any necessary lighting needs to be used properly and wisely. Too much lighting, especially at nighttime, leads to light pollution and light trespass, and can be a nuisance to neighborhoods and communities. The International Dark-Sky Association (IDA) defines light pollution as "any adverse effect of artificial light", and light trespass as "light falling where it is not wanted or needed".
Below are guidelines on how to minimize the harmful effects of light pollution:
- Turn on lights only when needed.
- Light only the areas that need it.
- Lighting should not be brighter than necessary.
- Keep blue light emissions at a minimum.
- Light fixtures should be fully shielded or pointing downward.
Types of Light for Outdoor Lighting
Outdoor lighting usually uses low pressure sodium (LPS), high pressure sodium (HPS), metal halide (MH) and light emitting diode (LED) technologies as possible sources of light. Low pressure sodium (LPS) lights emit a yellowish or pumpkin-colored light but is very energy efficient for environmentally sensitive areas. High pressure sodium (HPS) are almost the same color and are mostly used for street and roadway lights in cities. Metal halide and LED provide an option for white light, with the advantage of LED having a dimmable option to save on energy and further reduce light pollution.
Warm Light vs. Blue Light
Having fully shielded lighting is not enough because the color of the light is just as important. Since metal halide and LED emit white light, it means they have large amounts of blue light in their spectrum. Compared to yellow light, blue light has a more brightening effect on the night sky, which makes it important to lessen the amount projected outward and upward. Blue light also has potential adverse effects on human health and wildlife such as turtles. The recommended lighting color temperature by the IDA is 3000K and below for outdoor lighting.
In the color temperature spectrum, the lower color temperatures that have more yellow are referred as "warm", while the higher color temperatures that have more blue are "cool". LPS and HPS lights are more towards the warm light, which makes them ideal for outdoor lighting. LED lights with 3000K or lower color temperature also satisfy the warm light requirement.