Ziel
An intercomparison of luminous flux measurements has been carried out on high pressure sodium lamps. A set of 5 carefully manufactured 250 W lamps were selected as transfer standards because of their stability, and circulated on a radial basis for measurements at 14 different European laboratories. Five 95 V 1000 W tungsten filaments were also circulated in parallel, in order to distinguish the differences between the basic scales maintained by each laboratory and the measurement problems set by sodium lamps. The measured mean luminous flux differences ranged from +9.8% to -6.1%, the standard deviation being equal to 1.75%. This figure would drop to 0.64% if only 8 laboratories were considered. Although, as expected, individual lamps showed fluctuations in output during use, these mean values proved to be more than adequate for the task of examining the ability of the participating laboratories to make photometric measurements on this type of sodium lamp and suggested that such lamps might well be used, if required, to provide secondary standards.
PROJECT MTR00096 PROJECT DEFINITION The project is very similar to the project on high pressure mercury lamps. This had shown discrepancies between the participants and because of the commercial importance of sodium lamps it was important to verify that the luminous flux can be measured correctly.