The effect of indoor daylight spectrum and intensity on viability of indoor pathogens on different surface materials

Abstract

ABSTRACTBuilt environments play a key role in the transmission of infectious diseases. Ventilation rates, air temperature and humidity affect airborne transmission while cleaning protocols, material properties and light exposure can influence viability of pathogens on surfaces. We investigated how indoor daylight intensity and spectrum through electrochromic (EC) windows can impact the growth rate and viability of indoor pathogens on different surface materials (polyvinyl chloride (PVC) fabric, polystyrene (PS), and glass) compared to traditional blinds. Our results showed that tinted EC windows let in higher energy, shorter wavelength daylight than those with clear window and blind. The growth rates of pathogenic bacteria and fungi were significantly lower in spaces with EC windows compared to blinds: nearly 100% growth rate reduction was observed when EC windows were in their clear state followed by 41-100% reduction in bacterial growth rate and 26-42% reduction in fungal growth rate when EC windows were in their darkest tint. Moreover, bacterial viabilities were significantly lower on PVC fabric when they were exposed to indoor light at EC-tinted window. These findings are deemed fundamental to the design of healthy modern buildings, especially those that encompass sick and vulnerable individuals.Practical ImplicationsLight is an important factor that influences occupant health.Healthcare Associated Infections (HAI) bring substantial costs on the healthcare systems hence new disinfection methods are always needed to minimize fomites especially with the increasing antibiotic resistance.We found that indoor light modulated by the EC smart windows can significantly reduce the growth rate and viability of pathogenic bacteria and fungi, which is mainly due to the high energy blue light spectrum at wavelength of 400-500nm.Pathogenic fungi are found to be more affected by the indoor light intensity, while indoor bacteria on surfaces are more susceptible to the light spectrums.These results also demonstrate the promising potential of indoor daylight exposure as an alternative for fomite disinfection strategy and expand the benefits of EC window as part of healthy building design in the future.