Light is a form of energy that exists as radiation or rays, and this energy is a small part of the electromagnetic spectrum. The electromagnetic spectrum also includes other kinds of energy, such as the higher intensity, higher energy microwaves and x-rays.
We know the energy in these waves can do amazing things. It can allow us to cook our food and see pictures of our bones. When we use the energy in microwaves to cook food we are actually aiming to break the bonds or links between molecules. Energy in the form of light radiation can do the same thing.
Light sources, both natural in the form of daylight and artificial as in spotlights, lamps and fluorescent tubes, contain three components of energy. Understanding these three components will help us to better manage light in our collection storage and display areas.
The three components of light are:
Visible light is made up of the colours of the rainbow that together make white light. It is that part of the light spectrum we can see and it is this part of light that allows us to see colours accurately.
The UV and IR components of light, on the other hand, are invisible to our eyes, and play no role in our perception of colour. They are therefore unnecessary in a museum's lighting scheme. Furthermore, they can be damaging, and should therefore be eliminated or reduced whenever possible.
It is the UV component of sunlight that burns our skin. This can even happen when it is cloudy and level of visible light appears to be low. UV is the highest energy component of light and is therefore the most damaging. This is one reason that we recommend that sunlight does not fall directly on collection items.
It is the IR component of light that we feel as heat. Heat buildup from lights in showcases or from direct sunlight through a window can hasten deterioration in a number of ways.