Dark Sky UK recognises that we need good outdoor lighting at night, but any required lighting be used thoughtfully. To minimize the harmful effects of light pollution, lighting should
- Only be on when needed
- Only light the area that needs it
- Be no brighter than necessary
- Minimize blue light emissions
- Eliminate upward-directed light
Choose Warm Lighting
It’s not just about where light shines, the colour of light matters too. Blue-rich light makes the night sky much brighter, disrupts wildlife, and harms our health. To protect the night, choose bulbs with a colour temperature of 2,700K or lower. These are called warm lights and give off a softer, yellowish glow. Avoid cool, white, or bluish lights, which contain much more blue and cause the most harm.
Types of Light (The Science Bit…)
Most people are familiar with incandescent or compact fluorescent bulbs for indoor lighting, but outdoor lighting usually makes use of different, more industrial sources of light. Common light sources include low-pressure sodium (“LPS”), high-pressure sodium (“HPS”), metal halide, and, most recently, light-emitting diodes (“LEDs”).
LPS is an old technology that is no longer being manufactured. It was favoured for use around observatories and some environmentally sensitive areas. Narrow-band amber LEDs emulate the colour.
HPS is commonly used for street lighting in many cities. Although it still emits an orange-coloured light, its colouring is more “true to life” than that of LPS.
In areas where it’s necessary to use white light, two common choices are metal halide and LEDs. One of the advantages of LED lighting is that it can be dimmed. Thus, instead of always lighting an empty street or parking lot at full brightness, LEDs can be turned down or off when they aren’t needed and then brought back to full brightness as necessary. This feature both saves energy and reduces light pollution during the night.
Because of their reported long life and energy efficiency, LEDs are rapidly coming into widespread use, replacing the existing lighting in many cities. However, there are important issues to consider when making such a conversion. See our LED Practical Guide for more information.
