During the Information Day organised by Alweco South Africa and Zanthe Flora in May in South Africa, Hilde Lonsain from Hortilux Schréder, informed the growers present about supplemental light. Light is a necessary part of the photosynthetic process, with temperature, humidity, CO2 and water/nutrients. The speed of the process is set by the restrictive factor. During daytime in South Africa this will not be light. However, between sunset and sunrise the right supplemental light will make photosynthesis of most crops possible. So instead of “sleeping”, the crop is active at night, and continues producing. This will result in higher yields, better quality and faster crops. Year round production with a constant quality becomes possible, increasing market opportunities. Another positive result of giving supplemental light to the crop before sunrise is prevention of a wet crop. As the crop is already active and heated the sudden temperature increase at sunrise will not cause condensation on it.

HPS vs Sunlight

High pressure Sodium lamps (HPS, as SON-T lamps) are most commonly used for supplemental light in horticulture. These lamps give a very large output of PAR light (the visible part of radiation, used for photosynthesis); depending on the power of the lamp this output varies between 33 and 40%. For comparison, radiation of the sun has 45% PAR light. But where the remaining part of sunlight radiation is mainly Near Infra-Red light, which will not be absorbed by the crop, HPS lamps give approximately 30% Far Infra-Red light as well, which will be absorbed by the crop. This part increases the crop temperature.

Grow light installation

A grow light installation needs to be designed to meet the specific demands of the crop. Some crops, like chrysanthemum, which are harvested in one time, require equal light levels to obtain equal growth. Other, high growing crops like roses or cucumbers, require light deep in the crop, so also lower leafs will participate in the photosynthesis. In general, the light needs to be directed towards the crop, as light on the walls or the ground will not increase assimilation, but it will use power just the same! Hortilux Schréder can give customised advise and can supply the best grow light system for each crop. At Zanthe Flora, one bay of Lysianthus grows under grow light of Hortilux Schréder (8.000 Lux, 106 micromol). Jan Breeweg of Zanthe Flora has confidence the extra light will show results: “The extra speed of the crop during the winter will give me at least one extra crop per 3 years. This will pay for the extra investment easily!”

By Hilde Lonsain, Hortilux Schréder B.V