2000 Philips SON-HC 220W

The demo lamp shown here was made without a diffuse coating so as to show its internal construction which is of the last and most advanced generation of its kind. This 220 W SON-H is designed to replace 250 W high-pressure mercury lamps in their sockets while delivering close to 60 % more light with a 12 % reduction in power consumption. Philips was the first company to introduce neon-filled high-pressure sodium lamps designed to operate on mercury lamp ballasts. When the Dutch developed this technology in the late 1960s, they added a capacitive antenna around the burner so as to enhance the electric field and enable a reliable discharge ignition at the electric potential of 220–250 V mains.

Interestingly, it was found that the most effective location for the wire loop antenna resulting in the lowest ignition voltage lies at a point one-third between the electrodes. However, because of the manual assembly of the lamp which resulted in a relatively large variation in the antenna position, the starting voltage had a characteristically high variation, with some lamps not even starting properly under certain conditions (e.g. a too low mains voltage, etc.). This issue was solved by widening the antenna coil and by lowering the neon fill pressure, a design which became standard. Unfortunately, the latter change had a negative impact on the life expectancy of SON-H lamps as the enhanced sputtering of the electrodes during the runup phase results in a higher blackening rate of the burner extremities.

The design of Philips’s SON-H remained mostly unchanged for over three decades. In 2000 the wire coil antenna was replaced by a tungsten pattern sintered directly onto the ceramic burner. Since the same production method is used as for the company’s integrated (PIA) antenna, the small capacitive electrode could then be placed with high accuracy and with a much greater consistency than ever before, so the antenna size was reverted back to the original one. This conductive pattern is connected to the side frame wire via a bimetal strip which works as a thermal switch that opens when the lamp has reached it full regime. Such connection method minimises the electrolytic loss of sodium from the burner, which is crucial to the realization of a long lamp service life. The latter was extended to 26 kh at 50 % failures (8 kh to 5 % failures), also because the neon fill pressure was increased and the quality of the electrode and burner materials was improved.

Although the neon-filled SON-H lamps deliver much more light than the mercury lamps they replace (+63.8 % in the present case), they suffer from a lower lumen efficacy (-14 %) and a shorter life expectancy (-7 %) than standard xenon-filled high-pressure sodium lamps (the 250 W SON in the present case). As a result, in April 2015 Philips ended the sales of these lamps in Europe as they do not comply with the EC245/2009 regulation that came into effect that year. These lamps remained in production for the rest of the world until the end of 2025.