Mayrand (summarised by Lord and Lord, 2002, p. 411), identifies three functions of light at a museum exhibition:
– It makes the objects clearly visible;
– It creates contrasts and makes colours more vivid;
– It recreates the environment through special emphasis of certain parts of the architectural space.
Using natural light is a truly nature-friendly idea – it saves energy and it is better for our eyes, too. However, it also creates several problems in relation to making an exhibition sustainable. In broad daylight, sunshine is so intense that is damages objects made of organic materials and certain plastics. The source of light also makes a difference. If the ceiling is constructed mainly of glass or any other transparent material, light coming from above creates an open-air atmosphere. If it is the centre of the room that lights focus on, objects in corners or near the walls remain obscure or are completely hidden in the shadow. By the time our eyes accommodate to the light contrast and recognise the objects in the shade, we may have already left this hall. Even if we have a powerful light source, we must cater for artificial light to compensate for the loss of sunshine every afternoon or even in the morning on cloudy days. With global warming, using natural light is no longer viable because intensive sunrays damage the exhibits. Sunrays must be blocked by UV filters and the temperature also has to be regulated.
Artificial light is a flexible device: it can be used for the whole exhibition space, a showcase, a group of objects in the case or one single object only. Like a high stand, a spotlight provides a strong emphasis that indicates the importance of the object for the display. A simple row of lamps is cheap, but it radiates boredom, not just light. Some light bulbs are too strong to use, their UV radiation creates much damage, although their effect is dramatic. Fortunately, exhibition lightning is a growing industry, and we have an increasingly appropriate selection of devices to choose from.
Lamps have connecting cables that may spoil the overall effect of an exhibition, although visitors do not pay much attention to them. If the use of lamps is inevitable in an installation and they cannot be hidden or placed above the viewing level, they should have a modest shape and colour, in order not to steal the show from the real exhibits.
 Contemporary museums pay attention to light damage much more than was customary before. As a result, visitors often complain about dimly lit exhibition halls.