Outdoor Lighting Basics

IDA-UK recognizes 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

Glossary of Lighting Terms

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.

Colour Matters

It is crucial to control upward-directed light, but we know that the colour of light is also very important. Some lights have large amounts of blue light in their spectrum. Because blue light brightens the night sky more than any other colour of light, it’s important to minimize the amount emitted. Exposure to blue light at night has also been shown to harm human health and endanger wildlife. IDA recommends using lighting that has a colour temperature of no more than 2,700 Kelvins.

Lighting with lower colour temperatures has less blue in its spectrum and is referred to as being “warm.” Higher colour temperature sources of light are rich in blue light. IDA recommends that only warm light sources be used for outdoor lighting.

several diagrams showing the light spectra of various types of artificial and natural light.
Sunlight vs L.E.D. vs Florescent Light Spectra Comparison