For the last few months I’ve been undertaking a light survey of all the gallery spaces in the Museum. There’s a lot of interest – from visitors and staff – wondering what I’m doing out in the galleries waving a curious little instrument around, so I thought I’d best blog about it.
Prevention is better than cure
There are two main aspects to the work of a Conservator. Remedial treatment is the actual hands-on work; it includes things like cleaning objects and adhering broken objects back together.
Then there’s preventive conservation which is everything we do to protect and preserve the collection. This includes things like controlling the environment in the galleries and storerooms to slow down deterioration, and implementing pest management strategies to deter the little beasties that could pose a danger to the collection. Part of our preventive conservation strategy consists of measuring and controlling the light levels in the galleries.
Materials differ significantly in their response to light exposure. Colour change – such as fading or yellowing – is usually the most obvious indication of light-induced damage. Another effect of light-induced damage is loss of strength, which may be evident as fraying of fibres, or embrittlement and surface cracking on objects. Objects with organic components – such as textiles, paper and natural history specimens – are particularly susceptible to light damage. Metals and ceramics are generally less affected.
Once it occurs, light damage is irreversible. For the majority of our collection there is no ‘safe’ light level, which means all light exposure causes some degree of irreversible damage. We constantly walk the line between making the collection accessible to the public and keeping it in the best possible condition.
It’s not just visible light that concerns us. Of special concern to the Museum is the proportion of ultraviolet (UV) energy reaching the objects, as this can be really damaging.
There are international guidelines based on scientific research which we try to follow to in regards to the light levels particular materials can be exposed to, and the length of time objects should remain on display.
The 2015–2016 Light Survey
To get a good idea of the light levels in the galleries I measure the visible and UV light hitting every case. Some cases have internal lighting – in these instances, I need to get inside the case to measure the light being emitted by the internal light source. It’s required some contortions, but it’s also been very fun.
The instrument I use to measure the light levels is an Elsec Environment Monitor. This nifty little instrument is about the size of an iPhone, and it measures visible light, UV light, temperature and relative humidity. For visible light, the light meter gives a reading in lux. UV radiation is expressed in microwatts per lumen.
Light vs dark
Right now I’m still at the data collection stage of the project. Once all the data is collected and collated, we’ll have a good idea of the priority areas that need changes in light levels. I’ll make recommendations based on my findings, and we’ll look at making the light levels more appropriate by switching out light globes, adding filters to the light sources or adding filters or shades to the windows.
Light damage is cumulative, which means it’s the total exposure over time that matters. Reducing the amount of time an object is on display (and thus exposed to light) can make a huge difference in terms of prolonging the life of the object, so I will also be proposing rotations of the most light-sensitive objects on display, to give them a rest. This will give us the opportunity to showcase more of our collection and put objects on display that people may not have seen before.
As you can tell, there are a lot of factors to consider when lighting our gallery spaces. Light is essential to be able to view the objects on display but there is a very fine balance between displaying our objects so they are easily enjoyed by all visitors, and protecting the objects on display from light damage.