Plant growing 4 phosphor fluorescent lamp having a photon flux ratio of

Abstract

The invention provides a fluorescent lamp for plant growth capable of controlling morphology in terms of grass height, area and shape of leaves and so forth, approximating those obtained under natural daylight, while effectively promoting photosynthesis of the plant. The fluorescent lamp has a glass tube and a fluorescent layer formed on the inner surface of the tube and composed of four fluorescent components having light emission peaks in the bands of 440 to 460 nm, 540 to 560 nm, 600 to 620 nm and 700 to 800 nm, respectively, said fluorescent layer having the PF ratio ranging from 0.8 to 1.2 in terms of the ratio between the photon flux PF contained in the wavelength band of 600 to 700 nm to that in the wavelength zone of 700 to 800 nm. According to the invention, the spectral characteristic of the fluorescent lamp is so selected that light in the wavelength band of 700 to 800 nm, which influences the morphology of the plant and elongation of the plant, in addition to the light in the wavelength band of 400 to 700 nm, which is effective in photosynthesis, is applied to the plant so as to attain growth substantially equivalent to that obtained under the natural light.