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Is white light the right light?

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22.08.2005

Street lighting in the UK could better cut crime, promote feelings of well-being and enhance sight for pedestrians, according to a report published today. By using the wrong type of lighting councils are missing an opportunity to reduce both the fear of crime and pedestrian accidents, and are spending more than they need to on powering street lamps.

The paper, published in Lighting, Research and Technology argues that while UK councils traditionally use orange sodium lamps for their street lighting, whiter lights of the same wattage tend to create an environment that is perceived to be brighter. This has not been examined before due to a misunderstanding in the way the eye perceives brightness when the surroundings are dark.

Dr Steve Fotios of Sheffield Hallam University, and leader of the study explains, “The eye uses two photoreceptors called rods and cones to see light and colour. The cones, the primary photoreceptor for daytime vision, are the underlying basis for conventional photometry - the measurement of brightness with a light meter. However, at night-time under street lighting the rods also contribute to vision, and since the spectral sensitivity of rods is different to that of the cones, measurements made using conventional photometry are likely to be flawed. When you take the rod response into account, white lights could be more effective at night-time than is suggested by the cone-based light meter.

“The lights we use on our streets have huge effects on an area and the well-being of the people using that area, both in a practical and emotional sense. For example, well lit areas are though to be safer and therefore fear of crime is reduced. From a practical point of view, the better lit an area is, the less likely there are to be accidents, from tripping over kerbs and loose paving stones to being hit by vehicles.”

This study was funded by the Engineering and Physical Sciences Research Council (EPSRC).

Lorna Branton | Source: alphagalileo
Further information: www.shu.ac.uk

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