RLOD#41 (2020.07.17) 1979 СПО “Светотехника” ДРЛФ 400-1

Shown here during its run-up phase is a Soviet horticultural mercury lamp of the second-generation released in the second half of the 1970s. These special lamps were first introduced in the USSR in the late 1960s by СЭЛЗ of Saransk, Russia, who built them according to design principles established by Philips a decade earlier. These first-generation lamps had an oversized ellipsoidal jacket half-coated with a light-reflecting material and a red-emitting phosphor, which enables a relatively homogeneous illumination from a low mounting height, without the need for reflector luminaires. The design was eventually improved with the use of a standard-sized bulb coated in the manner shown here, i.e., with a light-reflecting layer that covers one third of the bulb and a phosphor layer deposited over two thirds of the bulb, with the last third left uncoated. This change enables a higher red output (radiated by magnesium fluorogermanate here), important for the photosynthetic activity of plants, and permitted an even lower placement of the lamps. The high amount of blue-violet light that is characteristic of mercury lamps is also valuable as it compensates for the lack of natural daylight in the regions where those lamps where used.