QUALITY OF ADDITIONAL ARTIFICIAL LIGHT IN RAISING YOUNG PLANTS

The use of additional artificial light in raising young plants during the darkest season of the year is an essential part of greenhouse growing techniques at many latitudes.
Especially in Finland, where greenhouses are mostly situated at the northern latitudes of 60 – 65°, growing young plants of early greenhouse vegetables is possible only with additional artificial light.
Tomato, lettuce and cucumber are usually sown at the beginning of January, sometimes even in December.
The sowing time is in practice determined so that the young plants, after having been transplanted in greenhouses, will develop satisfactorily in natural light.

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.

tabel 1.

The amount of total daily radiation in November-March at Helsinki (60°9′ N), mean values of the years 1958–1964

November	23,99 gr.cal/cm2
December	11,83 gr.cal/cm2
January	23,59 gr.cal/cm2
February	77,72 gr.cal/cm2
March	217,24 gr.cal/cm2

Symposium on Vegetable Growing under Glass

L.M. Kurki

https://doi.org/10.17660/ActaHortic.1966.4.15