The instant invention relates to a process for enhancing plant growth in greenhouses or plant tunnels or over mulches by incorporating one or more yellow pigments or dyes into a greenhouse, mulch film or glazing and exposing the plants through or over such film to solar radiation so that specific and defined ratios of the light transmitted, emitted or reflected between 410 to 450 nm, 380 to 410 nm and 450 to 500 nm are obtained. A further aspect of the invention is the use of one or more yellow pigments or dyes as plant growth enhancing additive in polymeric films for greenhouses, plant tunnels or mulches or a coating for greenhouse glazing so that specific and defined ratios of the light transmitted, emitted or reflected between 410 to 450 nm, 380 to 410 nm and 450 to 500 nm are obtained.