DETERMINATION OF COMMERCIAL GROWTH ROOM TREATMENTS

Growing room and bench lighting units using fluorescent tubes are now widely used by growers in the U.K. In most cases 12 hour photoperiods are used, so that lights can be used twice in each 24 hour period. Many basic problems have now been solved. For example, data are now available from which it is possible to predict at a given age the "size" (=dry weight, leaf area, leaf number and number of flower primordia) of tomato and lettuce seedlings grown at temperatures between 15°C and 25°C, with radiation in the visible part of the spectrum between 100 and 300 joules per cm² per light period, and up to 9 times normal CO₂ concentrations, using accepted commercial spacings and growing periods.

At given levels of total daily radiation, however, some differences in growth due to different types of fluorescent tube have been found. Attempts are being made to account for these differences; this is considered to be particularly important because increased knowledge of effects of spectral composition on growth might lead to improved efficiency of utilization of light.