The invention relates to a method for affecting plant growth, comprising the steps of irradiating plants (P) during a lighting period having a start period and an end period using light beams (LB) emitted by a lighting device (2) having a plurality of LED (light emitting diode) lamps (21) emitting plant sensitive emission wavelength ranges and having separately adjustable emission intensity, increasing the emission intensity stepwise and/or continuously during the start period, and decreasing the emission intensity stepwise and/or continuously during the end period. According to the invention relative to each other said lighting device (2) and the plants (P) are moved in an at least in part rotary movement while the plants (P) are illuminated. Furthermore, the invention relates to a plant growing system for affecting plant growth by light, comprising: a plant holding device (1), and a lighting device (2) having a plurality of LED (light emitting diode) lamps (21) emitting plant sensitive emission wavelength r
