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

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%).