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Bartlett research found that lower levels of brightness are required for white streetlights than for yellow sodium vapour lights. Switching led to energy savings of 30–40%.
CO2 emissions
In the UK in 2005, there were 8.12 million lighting points on the country’s streets using approximately 3.14 TWh of electricity, meaning CO2 emissions of 1.32 megatons. 6.31 million of these lighting points were streetlights.
With the rise in environmental concerns, pressure grew on local authorities to reduce the level of public lighting in order to save energy. But street lighting is important for crime prevention and public safety.
Reducing energy use
One of the key indicators of adequate street lighting is for two people to be able to recognise each other at a distance of four metres.
By setting up a dummy street and using a wide range of lighting and experimental subjects, Peter Raynham (UCL Institute for Environmental Design & Engineering) showed that white lights with lower illuminance had the same benefits as brighter sodium lights.
Switching to white streetlights made it possible to maintain the benefits of street lighting but reduce energy use by a third.
The British Standard for Street Lighting
In 2003, the British Standard for Street Lighting was reissued with revised guidance based on this research. In particular, it permitted dimmer white lights to be used on subsidiary roads. As a result, there was been a growing move towards white lighting.
Switching to white lighting
All residential street lighting renovations since 2006 financed through Public Finance Initiatives have moved to white lighting. The number of white lighting units grew from 450,000 in 2008 to 1.45 million in 2012.
The reduction in energy usage has been significant. In 2012, the change to white lighting saved 112 GWh of electricity in the UK, and saved local councils over £10 million in electricity costs. This represents a total saving of 45 megatons of CO2 emissions in 2012, or nearly a tenth of the UK’s emissions savings that year.