Text: Joachim Ritter
Photos: CoeLux

10. Mar 2014

Daylight or not daylight?
The copy is no longer distinguishable from the original

As German legend would have it, people – namely the “simple” folk of Schilda – were already trying to bring daylight inside buildings at the end of the 16th century. They were not that successful in the undertaking, however. Their idea was to capture daylight in sacks, carry the sacks into the buildings and open them up in the rooms where the builders had forgotten to put in windows. A tall story indeed. But all the stories about the people from Schilda have a similar twist. It must have had something to do with the speed of light that left the people wondering why the light would not stay inside but quickly found its way out through the door again …

So what can be done when a space has no access to daylight, but we are not prepared to forego the essential effect it has on us? This issue has occupied many a designer and manufacturer in the past. In the last 30 years we have been witness to a number of more or less successful approaches. But as yet no concept has really been able to establish itself as the true solution.

And yet what the market is about to experience – and what will be presented on the occasion of Light+Building is nothing less than a sensation – in the truest sense of the word – or perhaps even a revolution…

After the many trials (and errors) and the experience gathered in the last three decades many have given up believing it is possible to create the perfect daylight effect in windowless interior spaces. Unjustifiably so – and a little too prematurely. The history of mankind has enough examples of the totally unrealistic one day becoming absolutely feasible.

Thus, when we talk about a daylight simulation, this must be so good, so convincing, that the human brain perceives the setting, based on the person’s experience of nature, to be authentic and accepts it as reality. Our body, in turn, receives this information and responds biologically and psychologically to it. None of the experiments that have been carried out (or installed) to date have come anywhere near achieving the effect of daylight without our brains exposing them as fakes. When we talk about daylight, it is not only a matter of the colour temperature or the spectral composition of the light, but also about the colour of the sky and the spatial structure and location.

There are two basic principles that play a significant role here. The first is the principle of Rayleigh scattering. This describes the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. Air-molecule density fluctuations preferentially scatter shorter wavelengths (blue light) and transmits longer ones (red light) of the sun beam. That is why we see the sky as being blue in the daytime with the sun’s rays becoming yellowish or reddish at dawn or dusk when the sun is on the horizon. If it is physically possible to reconstruct this effect, the result would be a typical blue-sky effect. Advanced controls allow the colour of the sky to be defined, adjusted or set to change dynamically.

The second aspect has to do with spatial depth. The convergence cue given by the eye to see the sun’s rays as parallel beams (to prevent double-image formation) leads to infinite depth perception. Even when the sun is not in field of view, sun-ray parallelism is interpreted as due to a source at infinite distance, which strongly impacts the perceived depth of field.

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The full version of the article can be found in PLD No. 92
And our PLD magazine app (iPad App Store) contains a media-enhanced version.

Find the video that introduces the system here.

Follow the discussion on artificial daylighting on LinkedIn.

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