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MONDO ARC

PANEL DISCUSSION : LED Gallery Lighting

Issue 62 Aug / Sep 2011


Paul James, mondo*arc editor, discusses the galleries’ conversion to ERCO LED lighting with Allan Tyrrell, Engineering Manager of the National Portrait Gallery; Dawson Carr, Curator of Spanish and Later Italian Paintings at the National Gallery; Steve Vandyke, Head of Technical Services at the National Gallery; and ERCO lighting consultants Nigel Sylvester and Steve Spencer.





Paul James (PJ): Good morning gentlemen. Could you start by explaining why and when you converted to the Optec LED system at your galleries?

Steve Spencer (SS): About two years ago Allan Tyrrell asked me to see him about the tungsten lighting in gallery 13 at the National Portrait Gallery as the old four-circuit track was obsolete. That’s when we looked at the LED solution.

Allan Tyrrell (AT): We were spending so much money on repairing fittings. I’d been looking at LEDs and thought that the time was now right. So we tested it in a small gallery room and I was encouraged enough to say yes, but it was only a small room and there were questions about the colour rendering and the reds.

Dawson Carr (DC): It was that experiment that made us go for it! We had been looking at the theory too much, but once we saw your system we decided we had to try it as well.

Steve Vandyke (SV): We started in gallery 62 in the Sainsbury Wing about a year ago. From that we went on to galleries 6, 7 and 8 in the Wilkins Building.

DC: This was done in conjunction with a renovation of the rooms and the removal of two dropped ceilings dating back to 1953. This opened the space up hugely, allowing much more natural light to enter the space. Our relatively greater success with the LED programme is down to the fact that our component of natural light is greater. There is only a small amount of natural light in the National Portrait Gallery and some of the negative reaction from your staff, Allan, was because of the blue light in the green rooms. Ours was much easier to integrate.

AT: Six months after room 13 we proceeded
to room 12. Most recently we completed gallery 14 in November 2010. All of these rooms had little natural light, but the next two rooms we are looking at, 11 and 4, are east/west facing so inevitably there is more natural light.

SV: We are currently refurbishing rooms 5 and 10, and that will be completed by the end of March. Then we move on to galleries 2, 4 and hopefully 12.

PJ: How successful has the changeover to LED been?

DC: The people who are sensitive to what we do (and who know how the items should look and what sort of light is appropriate for that task) absolutely love this type of light. Getting the conservators on board is key because their sense of colour is truly more refined than any of ours. We love LED lighting because its slight cooler light is closer to natural light than tungsten.

SV: This effect is highlighted in rooms 6 and 8.

DC: Yes, we have taken the light level down by over 20% in those rooms but it still looks very good to me.

SS: So the LED fixtures must be running at
10 watts maximum!

SV: We’ve been experimenting with the LED lighting and it’s been a learning curve. We’ve got to convince curators, our conservation department and also our scientific department that this is the right direction to go in. People are warming to them, as Dawson has mentioned, but we’ve got to be happy that we’ve got the optimum lighting arrangement and that means that we are not only experimenting with the number of fixtures but with light levels as well.

SS: So you are already using less than the original design of 150 lux that I initially did when the programme first started?

SV: Yes we are. The original design had more fittings per room than what we installed. I’m really happy with the energy efficiency – that is the main driver for me. Obviously the other driver is the quality of light.

DC: There’s another driver though and that’s for the conservators and scientists. The fact that we can run at a lower lux level means that less energy is hitting the works of art. I understand that measuring lux is a crude device but it’s still useful.

SS: You have a certain amount of lux hours for all of your pictures?

SV: We have a limit of about 12 kilolux hours per picture.

SS: So if you can run lower lux levels it means you can display the pictures for longer.

DC: In crude terms, yes. It’s interesting though because if I walked into the spaces and you asked me to guess the lux level I would guess that they are much more.

SS: Yes, they feel brighter, don’t they?

DC: Yes, there’s something about the quality of the light, the crispness. The peak in the blue was a concern for our scientific department but if you look at all the benefits they are very excited about this as well. Plus there’s the ten-year life expectancy...
SV: I’ve worked it out at between ten and twelve years based on about 3,800 hours a year.

DC: For us, in addition to the quality of the light that we know will get even better, the part we love the most is the control factor. In particular, the basic physics of LEDs that lets them be dimmed without changing the colour temperature. That fits in with what we’re trying to do in conjunction with using natural light.

SV: Different exhibits need different quantities of light. We were only able to dim down to 80% with the old system (without changing the colour temperature). Now we are able to dim down to 20%. So the beauty of LED lighting is there is no degradation in the quality of light, but it also means we can create more lighting for one exhibit and we can set scenes individually through the ERCO lighting control, which means we can satisfy the curators and conservators whilst using less energy!

SV: Throughout the years we’ve used ERCO products so most of the galleries already have the track installed, so with few modifications we can adapt the system to LED. This means there is little disruption with high gain and it also means we are future-proofing which is very important. I have been entrusted with our carbon plan and this means we are embarking on projects that are geared up to save carbon in the next ten years. This also includes the carbon tax that comes into affect in 2012.

PJ: Can you explain a little more about the carbon tax and how far it affects you?

SV: This is a government tax of (currently) £12 for every tonne of CO2 produced by a business in the UK. This will mean a payment of roughly £100,000 a year from the National Gallery. That’s the equivalent of a couple of exhibitions for us. Therefore it is even more important to see how much money we can save through initiatives like LED adoption as well as our obligation to CRC (Carbon Reduction Commitment Energy Efficiency Scheme). We can save hundreds of thousands of £’s a year purely through energy saving project initiatives, so we look at this partnership with ERCO as an important part of that.

AT: The biggest compliment I could make about the LEDs is that, in the two years since the initiative, we have not had a comment from the public about the lighting system.
Nigel Sylvester (NS): That’s a powerful statement!

AT: Yes, that means that what we are doing is acceptable because no-one has complained. Believe me we get a lot of complaints about all sorts of things like the state of the toilets etc, so people would complain if they didn’t like the lighting.

PJ: Is there anything that you would say the LED doesn’t quite work so well with?

DC: The only thing that I’ve noticed is that LED lighting does not complement three-dimensional objects like works of sculpture so well – at least with the flood lenses on them. I don’t know if it’s the six points of light as opposed to one but it does something to sculpture that evens out some of the plasticity. It wipes out the three-dimensional quality of sculpture. Conversely, one of the reasons why we do like its affect on paintings is that it doesn’t over-emphasise frames, which incandescent light can do when the gold jumps out and overwhelms the picture. The LEDs don’t do this yet, they emphasise the surface texture of the painting.

NS: This relates to the set of tools you have to do different tasks. In the LED spotlights a special lens determines the beam distribution. The ‘narrow spot’ characteristics are perfect for the play of light and shadow on a sculpture. At the moment you’ve got a great selection of LED characteristics, but there are more options that will become available to you. As it stands, from the same fitting, you can have five different beam distributions just by changing the lens.

AT: In our gallery people say that they can pick out different elements like quartz in the marble now, when using LED.

NS: Yes, what I saw was something that was better than when the halogen was used because it picked out all the content of the sculpture material. The detail came alive.

PJ: Is that because of the different colour temperature, though?

SS: It’s more about the different mix of colours in the beam. Tungsten has got a massive emphasis on red, whereas LED has a more even distribution between the blues and the reds. There is a spike in the blue that we’re trying to flatten out, but you haven’t got lots of red beam thrown onto every object that makes it look dirty and yellow.

DC: One of the problems that you’re facing with the acceptance of LED lighting is that we have made people accustomed to seeing works of art blasted with warm spotlights. It’s simply what they are used to.

SV: People don’t like change.

AT: The biggest criticism I’ve heard is regarding the colour rendering – the fact that it’s not in the 90s and losing the warm effect.

NS: There are two points to consider with the Colour Rendering Index. The first is that a CRI number cannot guarantee what you are going to see and the second is there is a compromise to be had in terms of luminous efficacy. We want you to have a performing product with a very good illuminance on the articles you are illuminating with a good colour rendering. If you try to increase the colour rendering any more, you inevitably reduce the light output.

SV: Yes, of course colour rendering is important but it’s only as good as your eyes. It’s all about human perception. Can you distinguish between an LED fitting with a CRI of 88 and something with a CRI of 95? My guess is no.

DC: Yes, for the vast majority of people you’re not going to see the difference. Just seeing the quality of light in Room 13 made up our minds about that.

PJ: The other issue is people’s perception of what colour rendering is. They may be actually thinking about colour appearance, different colour temperature for instance.

SV: Exactly. LEDs are not comparative to tungsten so therefore it’s questionable whether you should use CRI as a measuring device of quality.

NS: I think LED lighting is a major chapter change and it’s galleries like yours that are at the forefront of this change. We are so used to warm light but the cooler light of the LED is a better representation of daylight and that is the optimum environment for viewing paintings.

SV: In fact, when you move from a tungsten-lit gallery to an LED-lit one the perception is that the LED gallery is brighter. This isn’t the case – it’s the perception. This means you can dim the LED lighting even further to get the same perceived illuminances thus saving more energy.

AT: I’m also using less air conditioning, based upon our figures, because there is less heat. I’ve actually downsized our chillers because the electric load has gone down so much.

SV: LEDs are also great for our budget because we don’t have to lamp change.

AT: Oh yes, if we had LED fittings over two floors, which is my aim, I could reduce our maintenance levels enormously because we’re not employing the maintenance contractor to do so much.

SS: Don’t you currently change all your tungsten lamps every time you have a new exhibition?

DC: In a special exhibition you don’t want any lamps blowing so you just change them all every time.

SS: That’s a massive wastage!

SV: You’re talking 2-3,000 hours for tungsten to 50,000 hours for LED so it makes a massive difference to our exhibitions.
NS: And the 50,000 hours represents the time when it gets down to 70% of output and as the degradation is slow you won’t even notice.

AT: Won’t the problem be that within that, say, twelve-year period, ERCO will be developing new, brighter versions and we’re going to be buying them to supplement the Mark 1 versions we already have?

SS: Even if LEDs do become even more powerful, the development and design of the luminaires will still be geared towards the user requirements. Future luminaires will probably have the same lumen output but from less power, so it could advance from 12W to 10W, say. So it shouldn’t affect you too much.

SV: One other thing is the lack of UV in LED, so there is no need for filters. We worked out we got a 50% reduction in light output through the UV filters and lenses of the tungsten lamp.

SS: The thermal tests that the NPG has done are staggering...

AT: Yes, we used a thermal camera and found that the heat output from the halogen fittings was between 300 – 350°C, whereas it was 30°C from the LED ones. In other words, ten times less heat.

SV: That’s when I can factor in the reduction of our air-conditioning load.

PJ: So you are confident that LED lighting is here to stay for museums?

DC: I ask our scientists all the time if there is any possibility that we are going to rue the day that we used LEDs in twenty years from now. They think that, looking at the data overall, we’re not dealing with something we’re going to regret in the future. The spike in the blue has the conservationist scientists concerned about what it’s going to do to fugitive blues over a long period of time. But we assume you’re going to even that out eventually.

NS: The LED starts in the blue spectrum and you put phosphor coatings over it. So the LEDs with the better colour rendering will have a lot more coatings on it, thus killing the light levels.

SS: This also means you can’t direct the beam so well. ERCO, of course, specialises in different types of light distribution, but if you add too many coatings you’re just going to get a splodge of light. You can’t do anything clever with it like pick out detail in sculpture. When we’ve slightly reduced the blue to the red side and the colour rendering will be slightly higher, we think that’s going to end the argument.

DC: Another advantage is the size of the fitting and the reduction of visual clutter in the ceiling, especially in the small gallery rooms.

SS: The new Logotec LED range has an even slimmer profile because we design our own electronic circuit boards and control gear that don’t require a separate housing.

NS: The Logotec LED is the first product developed by ERCO purely around the LED, whereas the Optec, prior to its LED adoption, was based on conventional technology. So where you’ve got trailing edge dimming on track you can set the Logotec LED spotlights to 60% for instance. In the past you could not dim it externally, but now, with the new electronics, you can set an upper limit to each individual spotlight and then dim the whole system.

DC: I like the sound of these! I think we should look at those next...

www.erco.com

www.nationalgallery.org.uk

www.npg.org.uk

This article was first published in ERCO’s in-house magazine Lichtbericht issue 92 in April 2011 with the help of the editor.

 

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