Led lights cause a “hangover effect” to plants

Urban areas are certainly not welcoming environments for plants. The poverty of the soil, the pollution and the artificial nature all around have partially selected over time the species that can grow in the city. Public lighting also has a negative effect on vegetation. And we are not talking about the arc bulbs of last century’s street lamps but about LED systems, the most efficient of the technologies available in terms of energy saving.

About 60% of Italian municipalities have replaced old plants with these new, more sustainable sources in recent years. But for some trees such as plane trees and linden trees, very common in tree-lined avenues throughout Italy, these low-consumption light bulbs have a light spectrum with a peak in the blue region which slows down the reflections. The effect is similar to that of a hangover. Near a light source, the photosynthesis activity of the tree continues even after sunset. But in the morning, after a hangover, the leaves struggle to absorb carbon dioxide. While in the specimens of plane trees and lindens that live in natural light this phenomenon does not occur. This was revealed by research by the University of Pisa recently published in the international journal Science Of the Total Environment.

But if the LED lights are not suitable what are the alternatives?

The study compared 15 specimens of each species, five in natural light conditions and the remainder exposed to a LED lighting system thirty centimeters from the canopy. “Both the linden and the plane tree were affected by artificial light with what we have called an effect similar to hang-over – explains Ermes Lo Piccolo, arboriculture researcher and one of the authors of the study – But this lighting technology has a negative effect more on the plane tree because it delays its autumn quiescence”.

Plantains, like many other plants called deciduous, lose their leaves in autumn and enter a sort of vegetable hibernation while waiting for spring. “The trees of this species that grow closer to the light sources, on the contrary, keep a part of the crown even during the cold season – he adds – so it becomes more vulnerable to frosts and, in the event of heavy snowfalls, the very stability of the tree can be affected. ‘tree”.

But how can we intervene on public lighting to protect these trees without giving up energy savings? As part of the ministry’s program reserved for research projects of relevant national interest (PRIN), the Universities of Pisa and Florence presented a study program entitled StreetTLAMP to develop a new LED technology with a light spectrum acceptable also for plants that live in urban environments. “The alternative – concludes Lo Piccolo – is to select over the long term those species, such as the common plane tree, which are more sensitive to artificial light in order to design cities in a different way”.