MUSEUM LIGHTING / EXPERT OPINION MUSEUM LIGHTING / OPINION
Kevan Shaw of KSLD argues that, despite the LED industry’s greatest efforts, solid state lighting is not always the best solution for museum lighting. Take the Holburne in Bath, England for example.
MUSEUM LIGHTING, NOW
We recently completed work on the Holburne Museum in Bath, UK. Nearly four years ago when be began work on the project the lighting market was a very different place than it is now. At that time, and while we were still designing, we were watching LED development closely and at the point where the decision had to be made we opted for Tungsten Halogen as the primary display light source. I am confident that we made the correct choice and believe this has been confirmed by the successful results achieved. If I was making the same decision today it would be next to impossible to choose Tungsten Halogen. In a relatively short time we have seen radical changes. We are seeing huge pressure to reduce energy use, partly to address the sustainability issue but also to address increased costs of operation through rising energy costs. We are also seeing legislation play an increasing role in lighting design. On one hand meeting building energy efficiency targets set by the UK Building Regulations, on the other dealing with the impacts of European Energy Related products legislation that limits what lamps, control gear and, potentially, control system designs may be placed on the market. Looking back at the Holburne, sustainability was very much a design consideration. We worked hard to achieve usable daylight for the major exhibition spaces. For this to be effective a different philosophy on light exposure needs to be adopted. This is to look at the total exposure over time of objects rather than set arbitrary levels of illumination. Lighting designers can provide the tools for this, however it requires a much greater degree of management to be carried out by curators for this to be effective. It also requires a big catch up by many institutions that lend works to others. Understanding that exposure over time is the real determinant of deterioration due to light is not new, it is quite clearly set out in Thompson’s conservator’s bible, ‘The Museum Environment’ dating back to the 1960s. The approach was heavily reinforced in the ‘Control of damage to museum objects by optical radiation’ (CIE 157:2004) and will feature in the forthcoming revision to CIBSE /SLL LG8 Museums and Galleries. Without
this approach using daylight in museums, particularly in a country like the UK with capricious weather, will not be generally satisfactory for lighting exhibits. We are being led, or rather bulldozed down the road of considering LEDs as the primary choice for exhibition lighting. As it is some thirteen years since I first specified LEDs, I find it difficult to accept this is still new technology. Of course what is available on the market now is a far cry from the products available three years ago, let alone thirteen. Are they suitable for general display use in museums? The answer here is both yes and no. As we have to design schemes with considerably lower power density than we have in the past, LED based fittings must come under detailed consideration. This necessitates a cost - benefit analysis that covers more than the current price of fittings and the potential savings on energy bills over the projected long life of these products. Quality of light has become recognised as a vital element in museum display. For the most part visual access to museum objects is all that visitors are allowed and therefore lighting to enable you to get the most information and enjoyment is an absolute requirement. Over the last quarter of a century we have adopted the Low Voltage Tungsten Halogen lamp to provide this quality of light. It has near perfect colour rendering, is easily controllable both optically through modest scale reflectors and lenses and by dimming electronically. It has down sides: it operates at high temperature, emits infra red and Ultra Violet unless filtered in the lamp or externally, dimming dramatically reduces the blue end of the spectrum, it fails totally at end of life and this is relatively short (one or two years in a typical museum) necessitating frequent maintenance. We are told LEDs have none of these vices, however they have a whole bunch of their own. Firstly LED may be a mature technology but it is far from stable. Sadly it is unlikely ever to achieve the product stability that we are used to for other light sources as it is born of the semiconductor electronics industry where constant change is not expected but demanded. In a commercial
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The Holburne’s eclectic collection is enhanced by the broad spectrum of Mike Stoane LVTH lighting providing a richness to the wide variety of objects and materials in the display.
The Holburne’s temporary gallery is predominantly daylit with louvres controlling light levels and sun ingress. Subtle highlighting by dimmed LVTH balances changes in daylight and covers evening lighting all under automatic control to minimise energy use.
environment, where there are increasing pressures on efficiency and demands for ever cheaper products, not to mention higher profits for manufacturers, LEDs are following the same trajectory as personal computers and laptops, where, by the time you leave the shop, your purchase is already an out of date model. Unlike computers, where there is no physical limit on memory capacity and none yet apparent on speed of processing, you can always add another core. Converting electricity into light visible to humans has
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