Photoluminescent Materials for Urban Cooling: A Novel Approach to Quantify Their Contribution to Energy Savings and UHI Mitigation

Nowadays, the Urban Heat Island (UHI) effect represents a significant challenge for our cities, contributing to increased energy demand, reduced thermal comfort, and heightened environmental stress. To address this issue, innovative materials with photoluminescent (PL) properties are emerging as a promising adaptive strategy for lighting energy saving and passive cooling in the built environment. Indeed, these materials are able to re-emit a portion of the absorbed incoming radiation as light, even persisting after the end of the solicitation. However, quantifying PL, and thus its absolute effect on the urban energy balance, remains a challenging task for the scientific community. This difficulty arises because traditional analytical methods often fail to distinguish between light that is reflected and light that is re-emitted. To overcome this limitation, this study proposes and experimentally validates a novel procedure to detect the effective reflectance of a material by combining its optical and photometric properties.Five photoluminescent tiles with varying amounts of yellow-emitting pigments are selected as samples to test the proposed procedure. By isolating the re-emission phenomenon, the contribution of PL can be quantified in terms of reduced solar energy absorption, improved thermal behavior, and energy savings. This innovative procedure, applicable to all types of photoluminescent materials, sets the groundwork for their integration into the built environment. Such adaptive solutions could play a crucial role in reducing building energy consumption, enhancing thermal comfort, and mitigating the UHI phenomenon, ultimately contributing to more sustainable urban environments.