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:
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.
Energy efficient light bulbs
Incandescent and tungsten lamps
Metal halide lamps
Light emitting diode (LED) lamps
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.