Enterprises of the protected ground or greenhouse horticulture centres must have facilities for the necessary supply of heat, water, electric power, natural and artificial optical radiation. The long-term practice of plant cultivation has shown that in autumn, winter and spring, the basic limiting factor in transparent greenhouses is light.

The radiating mode of the greenhouses is one of the major and power-intensive factors of a microclimate. Therefore, in case of artificial irradiation, it is necessary to pay special attention to the minimization of power consumption, which is associated with the selection of a source, type of irradiation device, reflector configuration and location of the lighting fixtures.

The specific consumption (Sharupich et al., 2005) of power resources in the most common greenhouses in the world, which have one fructifying plant layer in the greenhouse volume, constitutes 40-55 mega-calories per 1kg of the product, which is by 40-45% higher than in the case of the technology of intensive cultivation of the culture, using the method of drop watering. The more productive and more power saving technology, i.e. the so-called Dutch technology is not advantageous in the environmental conditions of Estonia.

The latest research works of scientists have revealed that for the protected ground in the second heat-affected zone, including Estonia, multi-tier narrow-bench hydroponics is a more preferable technology. It allows to make more effective use of the greenhouse volume to ensure a simultaneous fructification of 5 layers, to increase the production yield per area unit by 3.0-4.0 times in comparison with the traditional technology, and to reduce the specific power expenses by approximately 70%.

However, the lighting maintenance of the cutting-edge technology which has a specific arrangement of the plant layers on inclined planes has not been sufficiently elaborated as yet. In particular, there are no technical decisions on the special lighting fixtures ensuring the increase of power efficiency of additional artificial irradiation. Therefore, it is essential to enhance the efficiency of one of the high energy consumption processes of artificial irradiation of the plants considering the spatial specificity of the promising multi-tier narrow-bench hydroponics technology.