Feel-good glass for windows

Above all, it promotes the passage through the glass of those wavelengths of light that govern our hormonal balance.

Most people prefer to live in homes that are airy and flooded with light. Nobody likes to spend much time in a dark and dingy room. That’s no surprise, since daylight gives us energy and has a major impact on our sense of wellbeing. It is a real mood lifter. But not everyone is lucky enough to live in a generously glazed home, and office spaces – where we spend many hours of each day – are often not exactly bright and breezy. Modern heat-insulating, sun-protection glazing for offices and housing doesn’t make things any better, since it isn’t optimized to allow the light that governs our hormonal balance to pass through: instead, a distinctly noticeable percentage of incident sunlight in this effective part of the spectrum is reflected away.

Anti-reflective glass that is more transmissive overall to daylight is reserved for certain special applications, such as in glass covers for photovoltaic modules or in glazing for shop windows. The aim with this kind of glass is to avoid nuisance reflections and to achieve maximum light transmission at the peak emission wavelength of sunlight. This is the wavelength at which the human retina is also most sensitive to light. “However, our biorhythms are not affected by the wavelengths that brighten a room the most, but rather by blue light,” explains graduate engineer Walther Glaubitt, a researcher at the Fraunhofer Institute for Silicate Research ISC in Würzburg. That is why he and his team have developed glass that is designed to be particularly transmissive to light in the blue part of the spectrum. The secret is a special, long-lasting and barely perceptible inorganic coating that is only 0.1 micrometers thick. “Nobody’s ever made glass like this before. It makes you feel as if the window is permanently open,” says Glaubitt. One reason the glass gives this impression is that it exhibits maximum transmission at wavelengths between 450 and 500 nanometers – which is exactly where the effects of blue light are at their strongest.

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