A method for increasing antioxidant content in plants, which includes: (a) placing at least one light transmissive material for adjusting or retaining light transmittance at certain wavelengths between a light source and photosynthesis receptors of the plants; and (b) passing a light emitted from the light source through the light transmissive material, wherein the light transmissive material adjusts or retains at least two of the following wavelength sections: the light transmittance at a section from 340 nm to 500 nm is 65% or less; the light transmittance at a section from 500 nm to 600 nm is 60% or less; and the light transmittance at a section from 600 nm to 850 nm is 83% or less.

A greenhouse screen is described with strips of film material that are interconnected by a yarn system of transverse threads and longitudinal threads by means of knitting, warp-knitting or weaving process to form a continuous product is disclosed. At least some of the strips include a film material in the form of a single- or multilayer polyethylene film having a thickness of 10-70 micrometers. Said film has at least 2-4 wt.-% SiO.sub.2 particles having a D.sub.50 of 2-10 micrometers. The film is advantageously used as a screen providing light scattering properties particularly suited for greenhouse applications.