First Philips high-pressure sodium lamp

Shown here is Philips's first high-pressure sodium lamp, the 400 W SO-N, first released on the market around 1965. It is significant in the fact that this is also the first high-pressure sodium lamp to feature modern thermo-compressive end seals, a Philips invention and a superior technology that would eventually be adopted by all other lamp manufacturers.

Interestingly, Philips made a compromise between color and efficiency for its first sodium lamp of this kind as the intention was to market it as an efficient source of extreme warm-white light. The light color of this lamp is indeed significantly whiter and more pleasant than that of standard HPS lamps. However, this came at a severe efficacy penalty, so this strategy changed within a few years after introduction and the second generation released at the end of the 1960s (the SON/T 400W) was optimized for efficiency only, then resulting in the familiar orange light color.