I’ve been thinking a lot recently about light so this is the first in a series of posts about how and why we try to control the amount of light in our galleries. Conservators get very exercised about light, and with good reason: many objects are damaged by exposure to visible and ultraviolet (UV) light. The damage caused is irreversible and can include fading of pigments, bleaching, discoloration, embrittlement, shrinkage, cracking, weakening…. if we conservators had our way, all our objects would be kept permanently in the dark!
Of course, this is a museum, so our objects have to be on display a lot of the time. An important part of the conservators’ job, therefore, is to find ways to make our objects accessible without allowing them to become too damaged from display. Like most things, this involves a certain amount of compromise, and I’ll be talking about how we manage lighting for exhibitions in a later blog post.
A key aspect of our collection care programme is monitoring the amount of light there is in the gallery – both inside and outside the showcases. In the picture above, I’m using a hand-held light sensor to check the amount of visible and UV light near this showcase. I’m paying particular attention to this case because the Sami costume inside has been dyed with bright colours that are very vulnerable to fading in strong light.
This kind of hand-held sensor is really useful for doing spot checks where we’re concerned about the amount of light in a particular part of the gallery. We also use it a lot when adjusting the light levels for temporary exhibitions, or when doing periodic light audits throughout the gallery. Often, however, we need to monitor light levels over a longer period, and for that we use these:
This grey box might look like a walkie-talkie, but it’s actually a datalogger/transmitter that’s part of our environmental monitoring system. There are several of these boxes in our galleries: most of them just collect information about temperature and humidity, but a few of them also measure light and UV levels (you can recognise them by the two white dots on the front). Every half hour they send this data wirelessly to a computer in the museum office, where the conservators can monitor it. (The transmitters send the information using UHF radio frequencies, so they’re actually not unlike walkie-talkies…)
The graph above shows a typical week’s data from a showcase where we are monitoring light and UV (click on the picture to see a bigger version). The green line shows the amount of visible light and the purple line shows the amount of UV – luckily, the graph shows that there is no UV at all, which means that the UV filters on the glass doors are working properly! The transmitter has picked up light between 9am and 4pm on the first five days (which is normal for this time of year) but no light at all on the last two days. That’s because those days (7 and 8 September) are a Sunday and Monday, when the Polar Museum is shut and the gallery lights are turned off. This particular showcase also has a blackout curtain over it outside the museum opening times, and I will write more in a future blog post about some of the methods we use to control light levels in different parts of the gallery.