||This lamp is a prototype manufactured by COBR Polam - a small and semi-independent company which appears to have existed as the research and development laboratory of the Polish national lamp manufacturer, Polam. It is not believed that this lamp ever entered production, and was only produced in small trial batches.
The concept of a linear double-ended version of the high pressure sodium lamp was originally introduced by Osram-GEC in 1975, whose SON-L lamps comprised a quartz outer jacket just 20mm diameter. Furthermore the outer was gas-filled instead of the usual vacuum, the heat losses to the gas filling allowing the dimensions of the arc tube to be reduced so as to achieve a more compact light source - albeit with a small loss of efficacy. Owing to the similarly compact outer jacket the light source can be precisely located at the focus of compact reflectors to realise improved beam control.
This Polish example is similar in that it makes use of the slim quartz outer jacket, but its arc tube is operated in the usual vacuum containment. As such the arc tube dimensions are similar to standard HPS lamps. The outer jacket is based with R7s end caps and is unusually long, resulting in a lamp of 254mm length. It was presumably therefore developed with the intention of retrofitting this lamp directly into luminaires originally developed for 1500W linear halogen lamps of the same length. A pair of barium flash getters, one at each end of the lamp, are employed to maintain high vacuum. The arc tube is of a 3-piece design, the ends being frit-sealed to niobium tubes. Small PCA washers of a low-grade alumina, recognisable by the opaque white colour, have been added to reinforce the seals.