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Lighting solutions for museums are a fine art in themselves, and should not only display exhibition objects optimally but also simultaneously protect the works from damage. At OSRAM, engineers and scientists from various sectors have got together in order to implement the conceptual ideas of architects and planners in the best possible way with a technical product concept. They have brought together sound LED expertise, state-of-the-art control technology and project competence with decades of experience in photometric measurement technology and luminaire construction. The result is a system that will be of high interest for architects and planners with museum renovation projects, and is being used for the first time in the Lenbachhaus municipal gallery in Munich.
The initially most important requirement of light for art is to ensure the best possible experiences with artworks. The concept of the lighting installation was based on an idea by the light artist Dietmar Tanterl, and the meaning this has for the Lenbachhaus was derived from a finding by Wassily Kandinsky, one of the founders of the world-famous Blue Rider group of artists: when he painted an artwork in the morning he had to have a look at it again at lunchtime to see how the colours appeared in the midday light. The OSRAM project specialists from Munich implemented this by a combination of five various LED types in order to "mix" their light, similar to the ingredients of a recipe. The principal in fact is not new, although the solution in the Lenbachhaus lifts this concept onto a completely new level because it is not only a "static" mix that is generated with constant light colour.
Based on Tanterl's idea, flexible adjustments can be set between morning red-similar warm white light (3,000 Kelvin) and daylight-similar cool white (6,000 Kelvin), and with complete dimming. The mix was programmed to achieve a colour rendering index (CRI) of greater than 95 for almost 100 shades. In comparison, a standard fluorescent lamp for office applications achieves an index of around 80, and halogen lamps 100 – although both are not freely adjustable in terms of colour temperature. This technology is used, depending on the specific room in the museum, within three types of luminaire: cove luminaires, spotlights and so-called shed luminaires. The latter supplement daylight from the roof-lights in the upper stories of the Lenbachhaus and iare installed directly below the windows to radiate, just as natural light does, firstly into the 'shed' constructions and then indirectly into the exhibition rooms. The complete system is controlled by a tablet PC.
A major challenge was to mix the light of the diversely coloured LEDs, especially in the spotlights. "For a blend like this you normally need a longer optical system in which the various colours can mix," explained Julius Muschaweck, manager of the optics development team at OSRAM in Augsburg. "But the luminaire in the Lenbachhaus had to be as filigree as possible. We achieved that by more or less cutting the light into small components with around 60,000 lenses on a diffuser disc with a diameter of 14 cm, and then allowing this to radiate in the direction of the artworks in perfect harmony."
As well as ensuring perfect art experiences, the conservational aspect or protection of the artworks is of central importance with museum lighting. "This is not just highly important because of the repeatedly critical reporting of this topic in the media," emphasised Michael Reithmeier, manager of the project at OSRAM. "It's also a matter of conservational demands for artworks made to museums by the insurance companies." Fundamentally, ageing of artworks depends not on the method of light generation (incandescent, fluorescent or LED lamp), but on colour spectrum, illuminance and exposure time. Cool colour temperatures are more damaging than warm ones for most materials, and thus most damage potential comes from especially "cool" and invisible UV radiation. As a consequence, unfiltered daylight is the most damaging light source for art. The lighting solution in the Lenbachhaus does not generate ultraviolet radiation and in addition, the flexible control options make it possible to set the light to warm white if needed. In addition, together with the OSRAM LED developers from Regensburg the LEDs were specified to damage the material of the artworks as little as possible: with lower colour temperatures less than incandescent lamps, and with higher colour temperatures less than fluorescent lamps and daylight.
The municipal Lenbachhaus museum will be opening its doors for the first time on the 8th May 2013 following its renovation. It was modernised under the management of the construction department of the City of Munich and the architectural offices of Foster+Partners, and the lighting solution was implemented together with the engineering offices of Bamberger and Partner. Funding for the project was provided by the German Federal Ministry for Education and Research. A detailed byline project report will be available at the OSRAM press office when the museum is opened.