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<p>At present there is an increasing trend in night-time illumination of urban landscape, especially in historic and heritage cities, which is known to affect the growth and diversity of phototrophic biological colonisation forming subaerial biofilms (SABs) on architectural heritage. Although previous studies have demonstrated that phototrophic (mainly algal) SABs thrived well under blue LEDs, whereas red and especially green LEDs exert a biostatic effect, the optimal duration of illumination required to achieve these effects remains largely unexplored. In this study, ornamental LED illumination lasting 2, 4, 6 and 8&#xa0;h using red, green, blue and warm white (positive control), along with no LED (i.e. darkness, negative control) were compared over phototrophic SABs, with 16&#xa0;h of daylight, recreated in the laboratory for 35&#xa0;days. At the end of the experiment, SABs were analysed by PAM fluorometry and characterised their diversity by morphology characters, biofilm biomass was measured by wet weighing and cell counting and phototrophic pigment content quantified. A duration between 4 and 6&#xa0;h of green LED light, and at lesser extent red LED light, reduced SAB development, while a period of 8&#xa0;h of blue LED light was optimal for further growth. Both red and green LED light increased the proportion of cyanobacterial cells. Light colour, rather than illumination duration, influenced SAB community composition.</p>

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Duration of illumination of architectural heritage: a key methodological consideration to control phototrophic colonisation

  • 期刊论文

  • 发表日期：

    2026年7月24日

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  • Anxo Méndez,
  • Rafael Carballeira,
  • Stefano Bertuzzi,
  • Patricia Sanmartín

摘要

At present there is an increasing trend in night-time illumination of urban landscape, especially in historic and heritage cities, which is known to affect the growth and diversity of phototrophic biological colonisation forming subaerial biofilms (SABs) on architectural heritage. Although previous studies have demonstrated that phototrophic (mainly algal) SABs thrived well under blue LEDs, whereas red and especially green LEDs exert a biostatic effect, the optimal duration of illumination required to achieve these effects remains largely unexplored. In this study, ornamental LED illumination lasting 2, 4, 6 and 8 h using red, green, blue and warm white (positive control), along with no LED (i.e. darkness, negative control) were compared over phototrophic SABs, with 16 h of daylight, recreated in the laboratory for 35 days. At the end of the experiment, SABs were analysed by PAM fluorometry and characterised their diversity by morphology characters, biofilm biomass was measured by wet weighing and cell counting and phototrophic pigment content quantified. A duration between 4 and 6 h of green LED light, and at lesser extent red LED light, reduced SAB development, while a period of 8 h of blue LED light was optimal for further growth. Both red and green LED light increased the proportion of cyanobacterial cells. Light colour, rather than illumination duration, influenced SAB community composition.