Influence of Micro-Scale Surface Texturing on Light Distribution From Luminescent Downshifting Layers for...

Luminescent downshifting (LDS) layers in greenhouses modify the photosynthetically active radiation (PAR) spectrum to enhance plant growth, with surface texturing enabling a critical role in improving downward light extraction. The 3 mm-thick LDS layers incorporate two different dyes (Lumogen F Red 305 and Eu-coordination complex) and six micro-structures (cones, square pyramids, cylinders, half-cylinders, domes, and prisms) are systematically optimised to maximise downward-extracted (DE) efficiency of both converted red luminescence and unconverted (not absorbed by luminophores) sunlight. Monte Carlo ray-tracing simulations model small-area (25 cm²) and infinite-area LDS layers and their integration into a 10 × 4 × 2 m greenhouse. The highest DE efficiency (65%) occurs in the infinite LDS layers containing bottom-indented cylinders with an aspect ratio (AR) of 0.9. These results emphasise the importance of moving beyond small-area LDS layer performance to determine the amount of red light (converted luminescence as well as unconverted sunlight) that reaches the floor of a full-scale greenhouse, defined here as the red enhancement fraction (REF). The REF is maximised for a greenhouse containing Lumogen F Red 305 in Karlsruhe in winter (70%) using top-indented domes and bottom-indented cylinders (AR = 0.2), while smaller gains are made in summer (22%) and in spring/autumn (35%).