We know that sunlight is important to our health, regulating sleep and mood. A new study, however, suggests sunlight also keeps us healthy by destroying bacteria that lurk indoors. The sanitizing effects are impressively close to those of ultraviolet light.

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For their experiment, researchers at the University of Oregon collected dust from homes in Portland and placed it in dollhouse-sized rooms. The dust inside the tiny rooms — and the microscopic creatures that lived within — stayed there for 90 days under three conditions: exposed to daylight through regular glass; UV light alone; and total darkness.

When the team counted and inspected the bacterial samples, they were surprised by what they found. Lit rooms seem to harbor only half as many viable bacteria when compared to dark rooms, and nearly as few as those in the UV room. Researchers found 12% of bacteria in dark rooms were viable, compared to 6.8% in daylit rooms and 6.1% in rooms with UV light only, according to the findings published in the journal Microbiome. 

Ultraviolet (UV) light is a form of light that is invisible to the human eye, occupying the portion of the electromagnetic spectrum between X-rays and visible light. One of the biological characteristics of UV light is that it is germicidal – meaning it is capable of inactivating microorganisms, such as bacteria, viruses, and protozoa.

Today, UV light-based devices are used for drinking and wastewater treatment, air disinfection, the treatment of fruit and vegetable juices, as well as a myriad of home devices for disinfecting everything from toothbrushes to tablet computers. But soon enough, smart blinds that allow some of the solar energy to pass through and kill germs for us may become commonplace in our homes.

The study’s results were quite unexpected, however, because glass is known to block out most UV rays. The findings suggest that having a well-lit room can help protect residents from all sorts of infections. For instance, some of the bacterial species that didn’t survive the daylight rooms are known to cause respiratory disease.

“Our experimental and simulation-based results indicate that dust contains living bacterial taxa that can be inactivated following changes in local abiotic conditions and suggest that the bactericidal potential of ordinary window-filtered sunlight may be similar to ultraviolet wavelengths across dosages that are relevant to real buildings,” the authors concluded.

Next, the team plans to gain a more nuanced look at the relationship between daylight exposure and bacterial inactivation. This way, architects can then design the perfect windows that are just big enough to let enough light in to kill dangerous germs. But, perhaps the most important takeaway is that you should pull the blinds and let some of that light shine your room for longer during the day.