Luminance Survey — Light Levels

Illuminated River have created the first ever luminance survey of the Thames, to assess current levels of brightness on and around the river and identify where light spill, glare and pollution is occurring. We have done this to make sure the new artwork minimises any light pollution, sky-glow and direct light spill into the river.

Guest post by Jonathan Gittins, Associate Director at Atelier Ten

As the Illuminated River Foundation’s technical lighting designers and electrical engineers, Atelier Ten have been involved from the beginning as part of Leo Villareal’s winning team. Our aim from day one has been to ensure the lighting design minimises light pollution, sky-glow and light spill into the river and its surrounding areas and neighbourhoods.

What has been great about being involved from such an early stage is that we’ve been able to have a lot of input into the design. One of the first things we did before the visuals were created was to complete a luminance survey of the Thames, to address what the current lighting situation was and use it as a marker from which to make improvements. Nothing on this scale had been attempted before and we believe this is the first luminance survey undertaken for a broad stretch of the Thames.

Over two weeks, Jonathan Gittins and Wes Lloyd from Atelier Ten photographed every bridge and the surrounding banksides using Luminance IQ, a specialist software that converts photos into calibrate false colour images to reveal levels of luminance (brightness).

Luminance study of the Thames bankside: ‘We completed a luminance survey of the bridges and their surroundings; nothing on this scale had been attempted before’.

From the survey, we were able to plot luminance levels along the river, assessing the brightness distribution on and around the bridges in order to identify the most appropriate luminance level for each bridge. For this project, we wanted to make sure we were using just the right amount of light on the bridges so that they will stand out but not overpower their surroundings. Equally, we are acutely aware of the potential harm that spill light can cause and so wanted to ensure light is targeted on the bridges and not into the river or surrounding areas – the right kind of light in the right places. In many cases, we found that the bridges were already lit to very high levels and we are lowering these levels without losing visual impact.

Current luminance levels on Albert Bridge, which throws out more light than a motorway.

Wes and I also carried out a light spill survey to assess how much direct light from the bridges was currently spilling onto the Thames. Hanging out of a boat, (kindly borrowed from the City of London), we whizzed along the river and under bridges with our light meter, some doughnuts and paper cups of tea. While we were really able to take in the full beauty and history of the bridges, which have some truly remarkable latticework on their undersides, we were shocked by some of the current levels of light spill. Albert, Tower and London Bridges all have very high levels of spill which are significantly over recommended levels. Albert Bridge, in particular, throws out more than 20 lux, the kind of light levels you would expect to find on a motorway, not a river. Illuminated River’s new lighting seeks to reduce this spill by 75%.

The lighting levels for London Bridge were all very high. Illuminated River has reduced the lux levels on London Bridge from 25 lux to less than 5 lux.

We also discovered that in many areas, a lot of the light spill into the river was coming from street lights and over-lit buildings. Illuminated River aims to be a catalyst for wider conversations about improvement to public lighting. While the former lighting on the bridges ran all night, from dusk to dawn, we have convinced bridge owners that for our project, our lights should be turned off at 2am, and we hope to be an example to others to do the same. There is currently no cohesive lighting strategy for London (the City of London is the only borough with a public lighting strategy), and many commercial buildings on the river are over lit at night, while our great landmarks and monuments disappear into darkness.

Over lit buildings on the north bank by the Golden Jubilee Footbridges. Red colour shows luminance in excess of recommended levels.

By using LED light sources we will be able to make energy savings. Leo’s artistic vision of gently kinetic and subtle movement means that the lighting will typically only be run at 30% of its full output, resulting in further energy savings.

The beauty of modern LED lighting is that we are also able to select lenses for the light fittings that are individually optimised to focus light only where it is required on the bridge. We have also designed custom shields fitted to the lighting and adjusted to significantly reduce spill light into the river, which is very harmful to fish. On some bridges, such as London Bridge, this means we can reduce light spill almost completely.

‘custom shields have been fitted to the lamps to direct light more effectively and significantly reduce light spill into the river, which is very harmful to fish’. This diagram shows the effect of the light shield on London Bridge (bridge in grey), where light spill has been cut almost entirely.

Another great thing about this project is that we have worked closely with our partners, such as the Zoological Society London and other ecology specialists, to learn about how light levels affect Thames wildlife and ecology, and collaborate on shared solutions. For example, we were able to work with Dan from Thompson Unicomarine to check the impact of light on bats (though it seems we do not have any bats roosting or foraging near the bridges), and we learnt from Anna Cucknell, Marine and Freshwater Conservationist at ZSL, that much like (some humans) the 125 species of fish that inhabit the Thames don’t very much like breeding with the lights on either. Through these collaborations, we have been able to come up with a lighting scheme that respects these river residents.

Through this project, I have gained a new appreciation for the river and its bridges, not to mention having had some unusual experiences that I never would have otherwise. I have crawled inside London Bridge equipped with breathing apparatus and a harness to look at the cable routes (who would have known that it is actually hollow inside… or quite how much it trembles if you stand in the middle!) and I have hung off of bridges in human-sized ‘gantry’ buckets during lighting tests.

Hanging off London Bridge in a human-sized ‘gantry’ bucket: ‘not your typical experience on the day job’

Most importantly, though, right from the inception of the Illuminated River project we have worked to demonstrate how you can reduce light pollution and light spill, while still achieving beautiful artwork that enhances the public realm.