Spectral Utility Concept Guided Design and Evaluation of Light-Conversion and Thermal-Retention Agricultural Films

Abstract

Functional agricultural films improve greenhouse light environments and thermal management by regulating the transmission of solar and thermal radiation. However, current evaluation methods exhibit systematic bias. Light-conversion films are commonly assessed using red-light enhancement or chlorophyll-absorption matching, whereas thermal-retention films are typically evaluated using average infrared blocking rates, both of which neglect wavelength-dependent functional responses. To address this limitation, the concept of spectral utility (SU) was introduced. Four representative light-conversion systems and four thermal-retention materials were investigated, and photosynthetic spectral Utility (PSU) and thermal spectral utility (TSU) were established to quantitatively relate spectral modification to practical agricultural benefits. The results revealed substantial discrepancies between conventional and utility-based evaluations. Conventional spectral metrics and PSU produced different rankings of light-conversion performance, indicating that spectral enhancement does not necessarily translate into photosynthetic benefit. Greenhouse cultivation experiments further showed that crop performance was jointly governed by spectral utility and film stability. For thermal-retention films, TSU exhibited a stronger correlation with nighttime temperature increase (R2 = 0.95, p = 0.026) than the conventional average infrared blocking rate (R2 = 0.75, p = 0.136), indicating a closer relationship with actual thermal-retention performance. These findings reveal a fundamental distinction between spectral change and practical benefit. By introducing spectral utility as a wavelength-response-weighted descriptor, this work provides a unified basis for the evaluation, screening and optimization of functional agricultural films.