Thursday, 29 August 2013

Dazzled by the new street lights (not)

Cambridgeshire county council is running a project replacing street lights to save energy (actually it's a PFI so Balfour Beatty is running it) - and so are many other councils around the country. Street lighting is a very visible use of energy and excites a lot of opinions, both on the side of making savings and on the side of ensuring adequate lighting. The new lighting in Cambridgeshire is expected to halve energy use while maintaining adequate lighting levels. How is this possible and how much difference will it make?

An FOI request to Bristol council in 2010 reported that the average street light in Bristol at that time consumed just under 140 W [1]. That isn't a great deal when you consider that many homes used to use more than that in their living rooms - we had three 60 W bulbs in ours when I was little. However, now we are accustomed to using 15W CFLs instead, 140 W does seem quite a lot.

The most efficient type of light you can get in terms of lumens per watt is still the orange low pressure sodium lights. We tend not to like these, however, because the narrow spectrum means you only see things in monochrome. In fact, the national codes for street lighting recognise this and recommend that a lower light level is sufficient when white lights are used [3]. White street lights can use metal halides, compact florescents (CFLs) or LEDs.  Metal halides are often used for lighting sports stadiums as they produce a very white light. However, they produce UV, are prone to bursting at end of life and they are expensive. CFLs and LEDs are both increasing in popularity: Sheffield is installing LEDs [4] while Cambridgeshire is mainly installing CFLs. In Cambridge the new standard for residential areas is a CFL using only 36 W. However, for A roads and other places where higher light levels are needed we will have high pressure sodium lights of up to 150 W [5].

Apart from using more efficient bulbs there are other ways to save energy on street lighting.
  • Don't waste it - we want light near the ground, not in the sky. New lantern designs ensure that light is directed downwards which saves energy and reduces light pollution.
  • Don't light more than you need: the new lighting designs have reduced the number of street lights a little.
  • Some schemes involve dimming lights in the early hours of the morning - though total switch off is unpopular
From the point of view of safety it is more important that areas are evenly illuminated than that they are brightly illuminated. Our eyes are very good at adjusting to low levels of light but they are poor at seeing things in dark areas when the general illumination is good.

The new street lighting in Cambridgeshire is expected to reduce energy use by about half, from 18.8 GWh/year to 9.5 GWh/year and this will save £700,000/year [6]. (That suggests Cambs is paying 7.5p/kWh). The population of this county is about 613,000 people [7]. That means the savings are a little more than £1/person/year. In terms of energy they are 15 kWh/person/year: 0.03% of the average UK person's energy consumption.

I'm not saying we shouldn't be doing this - just that there are other ways we can save a lot more energy, for example in the home - see Never mind your computer, watch your router and Home Electricity Calculator Tool - or in the office - see The 2050 Office - a view from 2013 or Potential Energy Saving in Schools

Also there is more scope for saving on night time outdoor lighting by targetting businesses.  France now has legislation requiring all shops, offices and public buildings to turn off unnecessary lights (not security lights) overnight between 1am and 7am. This is expected to save €200m a year (€3/person/year) in energy costs and cut carbon emissions by 250,000 tons [8].

[1] Street Lighting Information (2011)
[2] Street lighting technology comparison, GRAH LED Lighting
[3] Save Money and Keep the Lights ON (Oct 2010) Institue of Highway Engineers)
[4] Street Lights (2013) Sheffield City Council
[5] Upcoming street works (download the designs to see the specs) (2013)
[6] Statement of Accounts 2011-2012
[7] Population and dwelling stock estimates and forecasts (2011)
[8] France calls time on wasteful overnight lighting (2013) Business Green


  1. The information I have from Cambs CC suggests a somewhat smaller saving of 8.5 GWh a year. A great shame this was all planned so long ago that they didn't deploy LED.

  2. I get very more information about street lights to save energy. So I really happy.

    semi flush lighting

  3. The real thruth is these are not saving energy. Old Lights (SOX) yellow lamps only 90w are being replaced by 150w to 250w (Now energy saved here!). Side Roads using 35w (SOX) Yellow light being replaces by 55w CFL Lamps, again not saving energy. This is why lamps are being taken out and creating dark area so the contractor meet the replacement criteria. If your really serious about energy saving, should be using L.E.D lamps, Green Cambridgeshire? Don't think so

  4. You have shared very precious information.

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