A method for increasing floral yield of a flowering plant includes positioning the plant between side lights at the onset of a flowering stage of the plant, such that the plant is flanked by the side lights. The method also includes irradiating lateral sides of the flowering plant along the total height via the side lights with light in a predetermined red spectrum range for a duration of the flowering stage, such that at least 80 percent of the light has a wavelength of between 580 nm and 780 nm. The plant may be positioned between first and second sets of equally-spaced elongated side lights on respective first and second lateral sides of the plant. Supplemental lighting devices may be attached to the plant, with an interior of the plant irradiated with the red spectrum light for the duration of the flowering stage using the lighting devices.