Leiden technology in rainbow artwork at Amsterdam CS
The Leiden astronomers Frans Snik and Michiel Rodenhuis developed the technology for the Rainbow Station artwork. Since 11 December, this large projected rainbow of light can be seen every day after sunset on the outside of the Central Station in Amsterdam. ‘We had to design light that would not blind the train drivers’.
‘Rainbow Station’ was conceived and designed by Studio Roosegaarde. The Studio wished to create a real rainbow by unravelling the white light from a strong lamp, just as a natural rainbow does with sunlight. The idea was to use a grating, an object that splits radiation on the basis of wavelength. But a grating produces straight rainbows, and the station required a round rainbow that would follow the curve of the station. Astronomers Frans Snik and Michiel Rodenhuis were called in to make this possible.
Together with optics experts from the North Carolina State University they developed a new kind of grating. The technology they used is primarily used to investigate exoplanets (plants orbiting around other stars than the sun). The grating breaks the light in such a way as to create a curved spectrum and a rainbow appears on the curve of the station.
‘It was really important that most of the light from the projector should end up on the station curve, says Frans Snik. ‘We had to make sure that there would be no ‘light leak’ that would blind the train drivers. With a normal grating, this would not have been possible, but we managed to do it by using a number of polarisation tricks. A normal grating also produces a mirror rainbow on the underside, but we also succeeded in eliminating this effect.’
The project was a unique experience for the astronomers. Snik: ‘We are of course used to working at night. But it was really interesting to be working with this innovative technology late at night in the cold at Amsterdam Central Station. This project allowed us to also take our technology one step further. And it was a great opportunity to find a different kind of social application for our astronomical research.’
‘Rainbow Station’ was designed to commemorate the 125th anniversary of the Amsterdam Central Station building. Rainbow Station can be observed after sunset on the large bow construction that spans the platforms. Throughout 2015, the rainbow will appear for a few minutes every evening after sunset. The precise time of its appearance is a surprise, just as with a real rainbow.
(16 December 2014)