Philips Ultrasol 5023 Self-Ballasted Mercury

In 1930 Philips introduced its first ultraviolet lamp for health care, the Ultrasol 5013. It emerged from the company's research into electronic tubes and was based on a full wave mercury rectifier with UV-transmissive Uviol glass. In 1931-32 it was replaced by this Ultrasol 5023, and like General Electric's American S-2 Sunlamp of similar power it combines a mercury arc with the therapeutic benefits of infrared heat.

At the heart of the lamp is spherical discharge vessel having a pair of offset triple-coil thermionic cathodes, between which an arc-shaped discharge bows upwards such that it is centred within the bulb. A sizeable quantity of mercury is present, the heat of a tungsten filament in the outer bulb causing a large vapour pressure to develop. The filament also acts as an electrical ballast for the discharge.

The spherical arc tube was chosen to elimitate cold crevices where mercury could condense, thereby raising its vapour pressure which is important to increase its efficiency of UV generation. Note the unusual glass-to-metal seals, which each consist of a pair of chrome-iron plates sealed into the sidewall of the glass sphere. An increased arc length is beneficial to raise its voltage and ensure that proportionally more of the mains voltage is dissipated in the discharge rather than the series filament, but too long an electrode gap would raise the ignition voltage above the mains level. This was partly overcome by opting for the spherical tube with short electrode gap, whose arc bows upwards and raises its length and voltage only when hot. Nevertheless, radiometric measurements reveal that this lamp is very inefficient, with about ten times less erythemal power than GE's S-2. As such it was rather quickly discontinued.
Manufacturer: N.V. Philips Gloeilampenfabrieken
Lamp Power: 110 Watts
Lamp Voltage: 220 Volts
Lamp Current: 0.505 Amps
Cap Type: E27s Skirted Nickel Plated Brass
Bulb Type: S-65 S-20½ (in eighths/inch)
Bulb Finish: Clear soft glass Transmitting to 280nm
Electrodes: C-9 filament Tungsten single coil
Atmosphere: Inner: Hg | NeAr Outer: Nitrogen
Luminous Flux: 800 lm
Luminous Efficacy: 6.8 lm/W
Radiant Flux: UV-A 0.17W, UV-B 0.05W Visible 6.1W
Colour Temperature & CRI: CCT: 2925K CRI: Ra93
Chromaticity Co-ordinates: CCx: 0.440 CCy: 0.415
Rated Life: Unknown
Warm Up / Re-strike Time: Approx. 10 minutes Approx. 5 minutes
Burning Position: Vertical base up
Overall Length: 180 mm 71/8 inches
Light Centre Length: 120 mm 43/4 inches
Factory: Eindhoven NatLab The Netherlands
Date of Manufacture: 1935 Week 43 Date Code: A43
Original Value: Hƒℓ 13.50 (1933)
References: 1) GB Patent 404,101, Improvements in or relating to electric discharge tubes, N.V. Philips Gloeilampenfabrieken, Priority 03-X-1931 (NL)
2) Kunst in de Philips-Reclame 1891-1941, F. Willebrink, publ. ZOO Producties, ISBN 90-74009-33-6, p.125
3) Philips Honderd 1891-1991, publ. Europees Bibliotheek Zaltbommel, 1991, p.77