Plant Growth with Artificial Sources of Radiant Energy

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Abstract
Comparative growth responses of certain herbaceous annuals to several sources of artificial radiant energy were investigated. The sources included un-filtered incandescent, water filtered incandescent, high pressure mercury arc lamps, and white and daylight fluorescent. The plant material irradiated was: China aster, variety Heart of France; spinach, variety Nobel; soybean, variety Biloxi; and tomato, var. Indiana Baltimore. The studies were made at 15[degree], 20[degree], and 25[degree]C and at varying photoperiods. The greatest height and fresh and dry wt. occurred with the incandescent sources. The water-filtered incandescent condition often produced taller plants with a lower percentage of dry wt. than the unfiltered incandescent. The shortest plants, with the smallest fresh and dry wts., occurred with the high pressure mercury arc lamp. Removing the 3654 A line in the near u.-v. spectrum of the mercury arc lamp failed to produce any significant increase in growth, indicating that this line is not responsible for the poor growth with this source. When the incandescent and mercury sources were set up in a single plot so that there were varying percentages of mercury and incandescent radiation, the height and wt. decreased as the % of mercury radiant energy was increased. The plants under the fluorescent lamps were of an intermediate type of growth which was vigorous and stocky except at 15[degree]. It appears that the differences in growth responses obtained with the various sources can be correlated principally with the differences in the respective spectral characteristics of the lamps.