With many of us spending more and more time indoors, it can be a struggle to get the amount of sunlight our bodies crave. Modern heat-insulating, sun-protection glazing doesn’t help, as it reflects a noticeable percentage of the incident sunlight in the part of the spectrum that governs our hormonal balance. Researchers at the Fraunhofer Institute for Silicate Research (ISC) have developed a coating for windows that lets in more light, in particular those wavelengths of light that have a beneficial effect on our sense of well-being.
While the human retina is most sensitive to light at the peak emission wavelength of sunlight, which brightens a room the most, Walther Glaubitt, a researcher at the Fraunhofer Institute for Silicate Research ISC in Würzburg, says our biorhythms aren’t affected by these wavelengths. Rather, it is blue light that has an impact on our sense of well-being.
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According to Glaubitt’s team colleague Dr. Jörn Probst, this is because there are special receptors at the end of the nerve connection that connect the human retina to the hypothalamus – the control center for the autonomic control system – that are sensitive to blue light. These receptors convert the blue light into light-and-dark signals that are sent to the part of the brain that functions as our biological clock, where, amongst other things, the nerve impulses regulate melatonin levels.
Melatonin levels help regulate the sleep-wake cycle, with high levels of melatonin caused by a lack of light leading to problems sleeping and concentrating, as well as depression and other psychological impairments. Seasonal Affective Disorder, or SAD, can be one potential outcome from high melatonin levels.
The new coating, which Fraunhofer researchers developed with the help of industry partners, is particularly transmissive to light in the blue part of the spectrum - at wavelengths between 450 and 500 nanometers, but its transmissivity is increased across the entire range from 380 to 580 nanometers, which the researchers say is the portion of the spectrum responsible for promoting well-being. When applied to a window, the inorganic coating is barely perceptible as it is only 0.1 micrometers thick. It also has no effect on the heat-insulating properties of the window.
Currently, the ISC researchers have only applied the coating to the side of the glass that faces into the cavity between panes. They believe that coating both the inside and outside of the window will up the light transmissivity at 460 nanometers from the current 79 percent to around 98 percent.
UNIGLAS GmbH & Co. KG, which worked with Fraunhofer to bring the coating to market maturity, is set to launch a triple-glazing product featuring the coating, which is marketed under the name UNIGLAS | VITAL feel-good glass. This product boasts light transmissivity at 460 nanometers of 79 percent. However, this is with the coating only applied to the side of the glass facing into the cavity between panels. The ISC researchers believe that applying the coating to both the inside and outside of the windows, as they plan to do in the future, will result in windows with around 95 percent light transmissivity at 460 nanometers.