Let There Be Light... But Not Too Much Please

In relation to last week's post about Picasso's Bottle of Suze (which has been taken back off display), I wanted to talk more about protecting art from light damage. It is a topic that has come up a lot recently at both the Kemper Art Museum and the Pulitzer Foundation for the Arts. Now at the Kemper protecting the art from UV damage is solely in the hands of the registrars and the senior staff. At the Pulitzer, on the other hand, I have a much more active role in monitoring the light levels in the building. Every thirty minutes I and other Gallery Assistants use a light reader to measure the amount of natural sunlight that reaches into some of the galleries. These activities peeked my interest and I took it upon myself to learn more about light and light readers, which I shall impart to you now.

The light reader we use at the Pulitzer measures in a unit called a foot-candle. Now my first thought was of several hundred tealight candles illuminating an object, but that didn't seem right. Then I thought of something more like this, but that didn't seem right either. In my mind the light cast by a small flame didn't seem that dangerous, aside from the potential threat of fire. So I did some research and learned that the 'candle' of foot-candle actually stands for candela, which is an international basic unit to measure luminous intensity. All this seemed rather clarifying and impressive until I found out that candela is actually Latin for candle, so I'm right back to where I started. It turns out a regular candle does emit a luminous intensity of about one candela. So does this mean that several hundred tealights could damage an artwork with their luminous intensity? Yes it does, especially at a high concentration or over a long period of exposure.

The 'foot' of foot-candle deals with the size of the area where the light intensity is being measured. This is not simply a foot, though, but is actually a sphere with a one foot radius from its central point. The light reader measurement is based on the central point of the sphere and assumes a uniform light source of one candela at that point. The amount of illumination that would be cast onto the inside surface of the sphere from the center is the the light reading.

At the Pulitzer we use this type of light reader. In order to operate it we hit the 'Vis' button, which measures the visible light. It also measures UV light and other environmental conditions, such as heat and humidity. It is a very handy and very expensive tool.

If it is determined that the luminous intensity in a gallery is too high there are a number of ways to protect the artworks or objects. If the source of most of the light is sunlight there are UV films and window covers that can stop 98% of ultraviolet radiation from ever entering the building. If the light source is electric there are similar products and sleeves for light bulbs. If it is a matter of visible light there are a number of simple ways to lower it, such as curtains, screens, or sometimes just covering the individual object. Since light damage is in fact inevitable, the best thing that can be done for objects is to keep them stored in dark locations and to only put them on display for short periods of time, like the Kemper did with Picasso's collage. You can read more about light damage and UV prevention here.

In my research I was also surprised to learn that UV light doesn't always have a negative effect on how people view art. There are a number of things that can be learned about a painting by intentionally shining ultraviolet light on it. Because it is a spectrum invisible to the human eye it can make things visible that we normally wouldn't see. Here is a great website where you can observe the before and after effects yourself.

What do you do at your museum in order to prevent the damaging effects of light? Have you ever used UV light to learn more about a painting or an object?