QUALITY OF ADDITIONAL ARTIFICIAL LIGHT IN RAISING YOUNG PLANTS
The amount of natural light around Helsinki (60°N) at the time young plants of early greenhouse vegetables are growing can be seen in table 1. The amount of light is indicated in terms of total radiation on a horizontal surface in gr. cal./cm2. The figures have been obtained from the measurements made by the Central Office of Meteorology in 1958 – 1964 (1), and they indicate the average daily values.
The amount of total daily radiation in November-March at Helsinki (60°9' N), mean values of the years 1958–1964