1956 Philips HO 450W

Philips began producing high-pressure mercury lamps around 1933, a year after GEC released the first lamp of this kind in England. Because of its high efficacy and longevity, the new technology quickly replaced incandescent lamps in many of their applications such as street, industrial and yard lighting, and a new market for vapor discharge lamps was thus opened in the early 1930s.

Early on, Philips (Netherlands) and Osram (Germany) designed their mercury lamps according to a specific output flux rating so as to better suit new lighting installations. Such practice originated in the early 20th century in incandescent streetlighting applications before the advent of modern metal vapor discharge lamps. The first mercury lamps introduced in the Netherlands and in Germany were rated for a 10 and 20 klm output and their power consumption was 265 and 450 W, respectively, which differed from those originally established by GEC in England (i.e., 250 and 400 W). Such peculiar lamp rating system worked effectively in Western Europe up until the 1950s, when more efficient medium-wattage mercury lamps operating at a higher pressure were introduced.

The HO 450 W shown here is thus designed to output 20 klm of light, which is slighly higher than that of 1 kW incandescent general lighting service lamps. The HO features a tubular burner made of a hard aluminosilicate glass and prodivided with platinum-coated narrow electrode chambers. The latter’s design limits heat losses at the burner’s extremities and thus ensures that the cold spot temperature remains sufficiently high under all operating conditions, with a position restricted to vertical cap up or down. That condition is necessary to the full evaporation of the dosed mercury which guarantees an operation of the discharge at one atmosphere, a key requirement to the realization of the lamp’s rated 44 lm/W efficacy. Typical of the Dutch-made HO lamp, a pair of springs hold the burner in place via holders made of stamped sheet metal and welded to the lamp frame.



The present HO 450W is a relatively late variant that features an outer bulb made of an aluminosilicate glass that can withstand an exposure to weather elements while hot, and a brass end cap coated with a layer of graphite lubricant in order to prevent seizure in the socket due to oxidation. Such measures were necessary as most outdoors luminaires used at the time had an open design.