Abstract
To analyze the light characteristics of lamps and to develop a methodology of artificial light irradiation in a contolled environment, the growth of spinach plant (Spinacea oleracea L.“Ujyo”) was examined under the same light intensities which were adjusted to equal illuminance of 10, 000lux and also adjusted to equal irradiance of 2.5 mW/cm2, using an incandescent lamp, an incandescent lamp equipped with infrared-absorption filter, a daylight fluorescent lamp and a ballastless mercury lamp with 13 hr photoperiod.
At equal illuminance of 10, 0001ux, plant height, fresh weight and flower-bud formation were scarcely affected. However, significant differences in length between the cotyledonary node and the shoot apex at day 38 were found among the various light conditions; the increase in length greatly inhibited under the incandescent lamp.
At equal irradiance of 2.5 mW/cm2, increases in plant height and in fresh weight were promoted under the fluorescent lamp, but were inhibited under the ballastless mercury lamp. Increases in length between the cotyledonary node and the shoot apex under the fluorescent lamp or the incandescent lamp with an infrared-absorption filter were much more pronounced than that under the ballastless mercury lamp.
Thus, different light conditions produced different plant responses, even under equal light intensities. Furthermore, the effects of light on plant growth appeared to differ with the methods used for measuring light intensity.
From these results, it was assumed that the selection and combination of lamps are important for artificial light irradiation in a controlled environment and also that development of a method to measure light intensities, which should satisfy requirements of biological experiments, is necessary for the adequate analysis of plant responses to environmental factors in an artificial light room.
