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by Kerstin Jürgen

LED spotlights from dot-spot illuminate the Devil's Cave in Pottenstein

The key to an extraordinary and sustainable nature experience: LED spotlights from dot-spot illuminate the Devil's Cave in Pottenstein

Created by nature in absolute darkness over thousands of years, only light enables genuine beauty and monumental splendour to become visible. The lavish dripstone magnificence of the Devil's Cave in Upper Franconia's Pottenstein, the largest of around 1,000 caves in Franconian Switzerland and one of the most beautiful show caves in Germany, has been highlighted anew for visitors from around the globe using light technology.

The lamps that previously caused visitors to stare in wonder at the magnificent stalactites and stalagmites around the 1.5-kilometre long circular route through the cave had become obsolete. The extreme environmental conditions in a dripstone cave test material and technology to their absolute limits. Very high humidity of up to 98%, dripping water containing minerals and a constant temperature of around 10° Celsius make the very highest of demands on the corrosion resistance and longevity of the material and on the lamp concept. Only LED technology, whose emitted light contains no UV component and which also radiates no heat, is therefore able to maintain the cave's integrity. In the past, conventional bulbs fostered the growth of mosses and algae, something which is unnatural and therefore undesired in this location. In combination with high numbers of visitors, particularly in the summer, the heat radiated by the lamps also led to an increase in temperature of up to 3° Celsius. This increased temperature influenced the growth of the dripstones. Lamps with conventional bulbs were therefore replaced by LED lamps back in 2007. However, the light output of these lamps had declined over the years. The further development of LED technology also offered new lighting options.

Since April of this year, the numerous halls within the Devil's Cave have been highlighted by 262 LED lamps from Franconian lamp manufactory dot-spot. The manufacturer of LED lamps and light solutions for the demanding outdoor and bathroom area develops series production and special lamps for use in the garden and landscape, in architecture and in ship building. The lamps are produced in the company's own manufactory.
Out of conviction, dot-spot manufactures the housings of built-in floor spotlights and surface mounted spots for permanent usage in the various areas from corrosion-resistant V4A stainless steel 316L. According to dot-spot founder and managing director Thomas Hödel, this is a crucial prerequisite for use in this very special milieu as well. V2A stainless steel would be attacked, and aluminium would break down over time. Lacquered steel would also quickly become rusty. In this regard, the lamps from dot-spot are predestined for this unusual application area.  

Following the light concept that was dreamed up many years ago by a light artist and which has been in existence since 2007, both monochromatic spotlights in colour temperatures of 3,000 Kelvin, 4,000 Kelvin and in red and blue blight colours as well as spotlights with RGB and RGB+white colour changes are used today. The light concept is optimised by the type and number as well as the positioning of various surface mounted spotlights from the Franconian light manufactory. In achieving this, the surface mounted LED spotlight clarios flex beam from dot-spot offers particular variability: by turning the front lamp unit, the spotlight's beam angle can be variably adjusted from 10° to 45° on site. This enables the interplay of light and shadow to be changed both during installation in this extraordinary environment and even at a later point in time.

The miniaturised LED object spotlight clarios-mini complements the range of lamps that is used in lighting up small niches and for even more focussed highlights. With a beam angle of just 6°, this small spotlight professionally highlights the pillar-shaped stalagmites and stalactites with clear outlines, picking them out from their illuminated surroundings.

The individual lamps and the scenario sequence are actuated using a DMX signal. To exploit the potential of the new lamps to the full, Horncolor Multimedia from Puchheim reprogrammed the scenarios and created new, impressive worlds based on the existing concept.


Together with the operating unit required to operate the low-voltage lamps, the DMX control units are accommodated and specially protected in a box, the so-called Multibox from dot-spot. The special feature of this Multibox is that its integrated membrane prevents moisture from entering the box but releases possible condensate into the environment. The operating and control units are therefore optimally protected for permanent use.

The cave's passages, which follow on from the enormous, 25-metre wide and 14-metre high portal, the "gate to the underworld", are illuminated by high-voltage LED spotlights that are also developed and manufactured by dot-spot. The clarios eco230 series lamps are connected directly to the 230 V power supply. An operating unit that is required for the low-voltage spotlights and which cannot be accommodated in these areas is forgone.

However, karst caves such as the Devil's Cave in Pottenstein not only make extreme demands on the material. Installation here is also a considerable challenge. R & S Held Elektro from Betzenstein mastered this professionally in Pottenstein.

The underground does not offer a single flat surface. The stalagmites and stalactites, which only grow by approximately 1 centimetre every 100 years, may not be damaged either by attaching the lamps or routing the cables or due to the movement of the installation technicians themselves. Improper installation of the lamps in an unfavourable location, a tool put down without thinking or a wrong movement could lead to the destruction of something that has taken thousands of years to develop.

The Devil's Cave in Pottenstein has been bathed in new light again since April 2019. With around 140,000 visitors per year, the cave is one of the most highly frequented show caves in Europe.

Project participants

Operator: Zweckverband Teufelshöhle, Pottenstein, Germany
Lamp manufacturer: dot-spot GmbH & Co. KG, Schwarzenbruck, Germany
Electrical installation: R & S Held Elektro GmbH, Betzenstein, Germany
Programming: HORNCOLOR Multimedia GmbH, Puchheim, Germany



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