Streetlights are an important part of infrastructure, often based on the assumption that more light equals more safety. While some countries only illuminate inside the settlements, others use streetlights for highways and country roads, too. In some European countries, bike-highways for commuters are built and illuminated during the entire night.
The energy consumption of this increased use of light is alleviated by the use of energy-efficient LEDs. But there is a rebound effect, resulting in more light points, more illuminated surface area, and brighter light levels. The light emissions from these installations cause a variety of ecological problems. Rows of light can fracture the habitat of insects, fish, and bats. Light spill brightens up the areas and the night sky over a wide region, interrupting biological rhythms and changing food webs, biodiversity, and ecosystem services.
To achieve ecologically acceptable streetlights, these consequences have to be taken into account in addition to energy consumption. So far, planning of streetlights is mostly orientated at the needs of car drivers and with the assumption that street use is constant during the night. Intelligent light planning has the potential to reduce light emissions in six ways:
- only illuminate roads when necessary; highways and rural roads usually do not need fixed streetlights
- reduce light levels to what is actually necessary to provide safety
- reduce glare for better visual performance
- focus light on the usage area and prevent light spill
- reduce light levels during times of low usage or use motion detectors to switch on light only if needed
- reduce the amount of blue-rich light to reduce the negative impact of animals
- combine non-lighting safety measures like speed limits, pedestrian crossings, speed bumps etc. to increase safety
A combination of these measures can reduce energy consumption and so-called light pollution, resulting in more sustainable streetlighting without negative consequences for safety.