May 25, 2016 at 5:40 pm #784
Different light sources provide different intensities of visible light, UV and IR radiation. In lighting the museum environment each has advantages and disadvantages. We can consider lighting in two main categories:
- natural, that is, daylight and
- artificial, everything from a candle (not recommended in museums) to fibreoptic systems
Daylight can be very bright and hot, and contains a high proportion of damaging UV radiation. The use of daylight as the sole source of illumination in a museum is rarely practical. It varies seasonally and is inconsistent throughout the day. It is difficult to direct evenly throughout a space. While conservators frequently recommend against the use of daylight, there are many who insist on its value in creating a desirable atmosphere for the viewer. For many of us, windows are a simple fact of life, sometimes our museum has been designed with windows or it is in a building that previously served another function. In these instances our challenge is to eliminate the UV, and achieve the most effective and pleasant lighting system we can. This is covered in the section How can light exposure be controlled? below.
Fluorescent lights are relatively cheap to purchase, economical to run and their life span is considerable, but most emit higher than acceptable levels of UV radiation. They should therefore be filtered with UV-absorbing film. This film can be purchased either as plastic sleeves which are placed over the tubes, or as acrylic sheets that are installed in the light unit itself. Low UV-emitting fluorescent tubes are available, but they are more expensive than the standard tubes. An advantage of fluorescent lights is that they do not generate much heat. This is one of the reasons that they are commonly used in show cases.
Energy efficient light bulbs
Energy efficient light bulbs are highly efficient compact fluorescent tubes. These bulbs emit UV light and would be difficult to filter with UV absorbing film. Therefore although they are energy saving they cannot be recommended.
Incandescent and tungsten lamps
These are available as the everyday light bulbs (incandescent) or as spot or flood lights (tungsten). They emit very low levels of UV, so filtering is not required.
They provide a ‘warmer’ colour of light that appears less gloomy than fluorescent lights, at the same level of brightness.
One of the disadvantages of these lights is that they get very hot. This has implications for their placement within a gallery, as objects near them can become heated. They also create heat problems if used within an unventilated display case.
Metal halide lamps
Metal halide lights have been increasingly used in museums over the last decade. They are more expensive to purchase than the lights referred to above, however they render colours fairly accurately, can be dimmed and allow greater flexibility in lighting design. While they do emit higher than acceptable levels of UV, most systems come with UV filters built in to the light unit.
Light emitting diode (LED) lamps
LED lights are a new form of lighting being proposed in gallery showcases. These are super bright lights that can be dimmed to museum requirements. They do not generate a great deal of heat and they emit low levels of UV. Currently available systems have not been very popular, however, because they do not seem to render colours very accurately.
As you can see there are advantages and disadvantages with most lighting systems. Recall that all light damage is permanent and cumulative. Natural daylight is an available and considered by some highly desirable light source for viewing artworks and object displays. This source of light is also the most intense and contains the highest levels of UV radiation. The UV component of light is not visible and therefore does not contribute to our viewing comfort. As it is highly damaging to collections it should be eliminated from museum displays by filtering.
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