Fluorescent Lamps as a Source of Light for Growing Plants

Abstract

A number of sources of artificial light have been employed in growing plants under controlled conditions. For various reasons, most of these have proved unsatisfactory. Carbon arc lamps give light of high intensity and good quality, but are costly to install and maintain. Other sources of light are poorly balanced spectrally for best growth, give off large quantities of heat, and usually necessitate the use of cooling systems when utilized in closed chambers. We have known for some time that Dr. D. R. HOAGLAND (University of California ) and Dr. F. W. WENT (California Institute of Technology) have been successfully using lamps of the fluorescent type in some of their experiments. Recently we have grown plants using 30-watt fluorescent Mazda lamps of both white and daylight types but of no other colors. These lamps were arranged so as to give an intensity of approximately 6oo foot-candles at the leaf surface and were the sole source of light. They were operated i6 hours each day. For purposes of comparison, some plants were grown with ordinary winter daylight and others in winter daylight supplemented (beginning at 4:30 P.M.) by 94 hours of approximately 6o foot-candles of light from an incandescent filament lamp. Cabbage, cocklebur, corn, kidney bean, Biloxi soybean, tobacco, and tomato were used. Plants under the fluorescent light grew most rapidly, had sturdiest stems, shortest internodes, largest and most numerous leaves of the deepest green color, and greatest fresh and dry weights. In general they appeared more like plants grown in summer sunlight than did those plants grown under either of the other two conditions of illumination (fig. i; see p. 706). Since these lamps give off a negligible amount of heat, they can be placed very close to the experimental material. They are much more economical and efficient in operation than incandescent filament lamps, and can be variously arranged in kind, number, and position so as to give different qualities and intensities of light. All points considered, these lamps have been found the best source of artificial light for growth of plants when used as the only source of light or as a supplement in winter in regions where daylight is of inferior quality and low intensity.AUBREY W. NAYLOR AND GLADYS GERNER, Department of Botany, University of Chicago. 715