Podcast: Cutting urban light pollution

LED street lighting

New LED street lighting in Reading

18 March 2014 by Sue Nelson

This week in the Planet Earth podcast, Roland Leigh and Joshua Vande Hey of the University of Leicester describe the work they're doing with Leicester City Council to cut light pollution and help the council save electricity.

To assist those who find text-based content more accessible than audio, a transcript of this recording is available below.

Sue Nelson: This time in the Planet Earth podcast, how monitoring the environment is helping a city reduce its energy bills. I'm Sue Nelson and this time I am in Leicester and even though it is during the day I am deliberately stood beneath a street light not far from the university campus near Victoria Park, because this is no ordinary street light - well at least it is not like any street light I've ever seen. It had the traditional base but at the top it has a rectangular black, almost like a step from a step glass, and underneath it are four rows of white circles, it must be some form of white lights and I can count almost four rows of, maybe, eight or ten of the lights themselves. We will find out why we're here in a moment as I am joined by Dr Roland Leigh and Dr Josh Vande Hey from the Earth Observation Science Group at the University of Leicester's Space Research Centre and also Manjeet Singh Virdee who is the Public Lighting Manager from Leicester City Council.

Manjeet, I'm going to start with you. What was I looking at and describing there?

Manjeet Virdee: Well you are describing the new LED lights, luminaire, that we are rolling out across the city.

Sue Nelson: It is very different from the lamp that is just down the road here which is a more traditional one and looks more like a sodium lamp.

Manjeet Virdee: It is and the programme that we are rolling out is a three year programme replacing all high pressure and low pressure sodium lamps. We have about 33,000 of these and at the end of the completion of the year we have clocked 10,000 conversions and we've got about 23,000 to go in the next two years.

Sue Nelson: What are the benefits then between the lamp above us, the LED one, so those little round dots I was talking about are obviously LED lights and the sodium lamp?

Manjeet Virdee: The sodium lamp is a 70 watt high pressure sodium luminaire which consumes just over 90 watts and it does throw some upward light, whereas in comparison to this LED light the majority of the light is downward, it's directional and it puts the light where you need it, on the road and the footpath.

Sue Nelson: Well that brings us to the two scientists who are here from the university, Roland Leigh, talking effectively about light pollution here.

Dr Roland Leigh: In the City of Leicester we are home to a number of keen astronomers who really like to see the night sky and understand it as well as the public who want to see the stars out thee and enjoy them, and what we have is a street that needs to be lit for public security, public information and we all like to be able to see where we are going at night, but we also have that reflected light bending up back in the atmosphere and coming back down to us as a night glow and as light pollution. So we have a very keen understanding and need to improve the situation and reduce light pollution.

Sue Nelson: And this led to a project called 'Night Mapping' that you are involved with, Josh. What did that actually involve?

Dr Josh Vande Hey: With our partner company called Blue Sky International we're developing a new instrument that can fly over cities and over rural areas and quantify the night pollution on the ground and also categorise sources automatically.

Sue Nelson: So you are taking aerial photographs effectively?

Dr Josh Vande Hey: That's right. By flying over the city and photographing the light pollution at night we can add some information to our current understanding from the cities well categorised and well understood light inventories to the private and commercial inventories which are not so well understood.

Sue Nelson: When you say private and commercial inventories, what do you mean by that?

Dr Josh Vande Hey: What I mean is whether it is bright lights that people may have installed on their homes or more often warehouses, retail parks, car parks. Many of these things are really used at night, the lighting is simply for advertising or perhaps for security purposes, but what we can do is say, well, look, there is this much light coming out from this location at night, is that much necessary, and we can inform those people, we can work with them to develop strategies to save electricity and lower the amount of light pollution.

Sue Nelson: So what sort of information have you got? If you go over the city is it the immediate information which may be an open air car park is throwing up more light than a shopping centre.

Dr Josh Vande Hey: That's exactly the sort of first questions we have asked. As you heard from Manjeet, the City of Leicester is doing really cutting edge work on managing and upgrading their lighting systems. What they don't have a good handle on is the sources that are off their grid - the private industrial light sources. So, for example, in our first flight over Leicester we saw that the car park on top of the Highcross Shopping Centre is the brightest spot in the city of Leicester and so we can identify these spots and then we can work with the city, with the industry partners and the commercial entities to come up with strategies that could be used to lessen the impact on these sources.

Sue Nelson: How has it been working with the council as a university? Has that been an easy or difficult thing - obviously Manjeet is standing right here so you've got to be fairly polite!

Dr Roland Leigh: So far it's been a very, very easy and interesting process. We first met with them about 18 months ago to understand what information they had and what processes they were putting in place, and then we've gone away and encaptured a data set that we think may be able to provide some new information.

Sue Nelson: What sort of data are we talking about?

Dr Roland Leigh: The data sets that they have are fantastic databases of all the lamps, all the light sources, the different kinds of bulbs and when they have been changed or are next due to be changed, so there's a great understanding of the public lighting infrastructure that we have, but what we can add to that is the understanding of how that light then interacts with the environment and all those light sources that aren't on the public grid.

Sue Nelson: In terms of environmental impacts, what are they?

Dr Roland Leigh: There's a number that you could perceive - one is the impact on humans in the city, how we humans interact, whether it is our sleep patterns or what we are doing when we are awake. There are also the ecosystems as well, whether it is bats or insects, how those systems are impacted by the different light patterns in the city.

Sue Nelson: And for you, Manjeet, I suspect it is a little more than saving the council some money, or is it purely economic that you are looking at this?

Manjeet Virdee: Oh yes it started with that with the authority making a commitment to reducing its carbon footprint by 50% by 2025 and we've been trailing and looking at the different light sources that are on the market and which are being developed by the manufacturers. The LED light technology has come on in leaps and bounds and also the price is something like half the price of what it was three or four years ago. In achieving the commitment that the authority has made, in procuring funding to replace all our low pressure and high pressure sodium lights, over the three year period we are hoping to reduce our energy consumption by more than 50%. We have actually seen that by changing to white lights we are getting just over 40% reduction in energy consumption, by just going to white lights, and by further dimming from 8 o'clock when the traffic count has gone down and then further dimming at 11 o'clock we think that we will probably hit 60% or more reduction in energy and carbon.

Sue Nelson: These are very impressive figures. Josh, what is it about white light that makes it so preferable to, what, let's face it the decades has been the accepted standard, the sodium lamp, the yellow light?

Dr Josh Vande Hey: First of all the LEDs have been optimised to be most efficient with the white colour that you see but also in terms of human perception when you use these white lights you can actually put fewer watts out to get the same perceived effect than you would in the sodium lamps.

Sue Nelson: So how do you characterise the type of white light that you see when you are flying over the city, because you are going to have different types of light aren't you coming up out into space effectively?

Dr Josh Vande Hey: That's right and in earth observation at the university we have a lot of interest and experience in spectroscopy and even in red, green, blue images, like a photograph, you can find out all sorts of things about the light source by looking at the ratios between the different colour intensities. So by looking at red versus green versus blue channels we can segregate the sodium from the traditional white light from the LEDs because of their different spectral signatures.

Dr Roland Leigh: Within the Earth Observation Science Group we use artificial light and sunlight to understand the environment which we work, so characterising our artificial lights is one of those aspects that is a natural offshoot of the spectroscopy that we do and the environmental science that we do and it is fantastic to be able to apply that understand of light sources to help manage this process of improving artificial lighting within our cities.

Sue Nelson: Manjeet Singh Virdee from Leicester City Council, Dr Josh Vande Hey and Dr Roland Leigh from the University of Leicester, thank you all very much for joining me in the city beneath one of these street lights. And that's the Planet Earth podcast from the Natural Environmental Research Council. You can follow us on Facebook and Twitter where we will post some pictures of today's recording. I'm Sue Nelson, thanks for listening.