Novel ornamental lighting used to halt phototrophic colonization on architectural heritage is effective under low and high daylight illuminance conditions

Abstract

Nocturnal ornamental lighting may serve as a biostatic tool to control phototrophic colonization on architectural heritage, though the influence of daylight illuminance on this effect remains unclear. This study is the first to consider the effect of the amount of daylight on responses to nocturnal lighting, by combining two levels of daylight illuminance (low, LDI, ∼2050 lx and high, HDI, ∼10200 lx), selected on the basis of field measurements, and three ornamental LED lighting conditions: cool white, warm white and amber + green (which has a biostatic effect on phototrophic growth) and a control (i.e. darkness). Subaerial biofilms (SABs) were generated using green algae (mainly Chlorella vulgaris and Klebsormidium flaccidum) and cyanobacteria (mainly Synechocystis sp.) isolated from biofilms growing on granite monuments. Changes triggered by the combination of daylight and artificial light at night were evaluated by biomass and diversity measurements, biochemical profiling, confocal microscopic examination and PAM fluorometry of mature biofilms. Cool white light enhanced biomass growth relative to the other conditions, while amber + green light halted biomass growth in both daylight scenarios. Amber + green light also decreasing the relative abundance of Klebsormidium flaccidum in LDI. Biofilm matrix production was reduced when illuminated with amber + green light in the LDI set-up. In the HDI set-up, all ornamental lighting conditions failed to alter the biochemical profile. However, amber + green light did reduce the Rdf vitality index compared to other conditions. Amber + green light effectively halted biofouling under both daylight conditions, potentially mitigating its impacts and enhancing the sustainability of urban heritage management through better lighting practices.