Horticulture lighting device and a method to stimulate plant growth and bio-rhythm of a plant

A method to stimulate plant growth and bio-rhythm of a plant, using solid state light sources, a reflective panel arranged between said light sources, and a wavelength converting member, all being arranged in a single unit, the method comprising the steps of:

• generating, by a first solid state light source and by a second solid state light source, direct red light having a maximum emission wavelength of 600 to 680 nm, preferably 640 to 680 nm;
• positioning an intermediate layer between said wavelength converting member and said first solid state light source;
• receiving at least part of said direct red light generating by said first solid state light source at said wavelength converting member;
• blocking by said reflective panel said direct red light generating by said second solid state light source from being received at said wavelength converting member;
• converting said received direct red light to far-red light having a maximum emission wavelength of 700 to 760 nm, preferably 720 to 760 nm, using said wavelength converting member;
• wherein a ratio of said direct red to said far-red light emitted is set by adjusting the amount of said direct red light impinging on said wavelength converting member from said first solid state light source and by independently regulating the intensity of light emitted by each of said first and second solid state light sources.