Lighting systems evaluation for indoor living walls

Living walls (LW) are vertical greening systems that are becoming popular due to their multiple social and environmental benefits. When LW are installed indoors, a lightening system is often required to ensure an appropriate plant development. This work assesses the performance of three artificial lighting systems on six indoor LW [0.7 m (wide) × 0.7 m (high)] placed at two distances from the light source. The plant species selected for the tests were Soleirolia soleirolii and Spathiphyllum wallisii, which are frequently used in indoor LW. Three different lamps were used in the experiment: incandescent (IL), fluorescent (FL) and metal halide (MHL) lamps, all of them with an input electric power of ≈250 W. Differences in plant growth were only observed when the LW were close to the light source (about 1 m) but not at greater distances (≈1.5 m). IL had the poorest performance. Despite the lower photosynthetic photon flux density efficiency of FL compared with MHL, FL light enabled plants placed in the upper LW (closer to light source) reached similar size to those grown under MHL. Plant quality attributes were generally not affected by light type or the distance to light source. IL and FL generated higher total water losses (i.e. transpiration plus evaporation) than MHL on a LW basis. When expressed per unit of LW area covered by vegetation, FL and MHL reduced water consumption by 34% and 56%, respectively, as compared to IL. Overall, our results indicate that both FL and MHL outperform IL and have a similar ornamental performance, whereas MHL are more advantageous than FL in terms of water consumption and annual cost.