(ESMH), and Kunsthaus Bregenz. A comparison of energy consumption with traditional buildings could be demonstrated in Hagen, where the existing Osthaus-Museum (OMH) is located directly beside the new Emil-Schumacher-Museum, which was opened 2009. Fig. 8 shows, that the annual energy costs of the ESMH could be reduced to 11.85 V/m2a by means of energy efficiency and to 2.71 V/m2a in addition by renewable energies in comparison to 29.67 V/m2a of the OHM. In terms of energy the classification of consumers and renewable sources is given in Table 2.
2.2. Light control
There are three tasks for the lighting in museums, visibility of objects, conservation of objects, and illumination of rooms, which can be realized by daylight and/or artificial light.
A good visibility of objects needs a minimum brightness, good contrasts without cast shadows, good colour reproduction, and
avoidance of glare. Depending on the kind of objects, e.g. two-dimensional pictures with micro structures on the surface,three dimensional sculptures or large exhibits like building monuments, the object lighting will differ a lot, especially as thereplacement of exhibitions requires a certain variety. For a true colour reproduction of artwork it is highly important whether daylight or artificial light sources are used and which colour rendering is applied on the room surfaces.
The conservation of objects often is in contradiction to good visibility, which increases with the brightness. The energy of absorbed light damages the object. The shorter the wavelength the higher the destructive energy of radiation is, thus UV or blue light has a higher damage factor than green or red. This means that a dark (absorbing) surface will be damaged more than a light one, and a red surface more than a blue one. In addition the sensitivity highly depends on the kind of material, e.g. paper is more sensitive than metal. Finallythe ageingof a material is influenced by the time of illumination. Because of these reasons maximum values for the energetic exposuretolight are defined. As 50 lux is the lowest value
for good visibility, this illumination often is defined as maximum value for sensitive objects of paper or fabric, while 150 lux are
defined for paintings on canvas. This regulation is vulnerable from the scientific point of view, as it does not consider the spectral component and the time of illumination. Therefore many museums try to define the conservation of objects by [4]:
- Definition of varying maximum illumination depending on light source - Limitation of maximum duration of exhibition
- Absolute protection against UV and blacking-out before/after visiting hours
- Individual classification of artwork in light sensitivity categories.