Philips Biosol MLU 500W Sun-Tanning

The Philips Biosol MLU (Mixed Light Ultraviolet) appears to have been introduced around 1950, at first in this powerful 500W model. It differs from its principal predecessors not only in its increased power, but also its facility to allow the UV and IR radiation to be separatedly controlled.

The arc tube is of an early hand-made quartz style having shrink-seals to molybdenum foils, and includes an auxiliary ignition electrode. The tungsten ballast filament is loaded less than in an ordinary mercury-blended lamp, because it was intended to allow this to be run directly on the mains as a pure infrared radiation source. It can also be brought into series with the arc to deliver UV+IR treatment, thanks to the 4-pin cap (of which only 3 pins are connected). Or with an external ballast, the mercury arc can be operated without the infrared component. The bulb is blown in a special soft glass whose transmission curve extends deep into the UV-C, which is now known to be acutely carcinogenic. A complex glass stem assembly having a Y-shaped press seal supports both radiation sources, its exhaust tube being fused into the side of the stem like old Jaeger-style incandescent lamps.

By 1951 this high power lamp had been joined by the smaller and simpler Biosol MLU 250W with fixed series filament and arc. That was considerably more popular on account of its much lower cost. By 1955 that had been replaced by the Ultraphil MLU 300W, following the obsolescence of the Biosol series due to the dangers of their short wavelength radiation. This MLU 500W rating was still listed as an ultraviolet radiation source for industrial applications late as 1966, but is believed to have been discontinued very soon afterwards.
Manufacturer: Philips Lighting Type 29960/20
Lamp Power: 500 Watts 200W arc, 300W filament
Lamp Current: 2.25 Amps
Lamp Voltage: 220-230 Volts
Cap Type: Jumbo P4 Philite insulator
Bulb Type: R-190 R-60 (in eighths/inch)
Bulb Finish: Inside Frosted UV softglass
Electrodes: Backwound Tungsten BCT emitter
Electrode gap: 60mm Quartz ID: 18.5mm
Atmosphere: Ar | Hg (2.5 bar) Outer: Argon-Nitrogen
Luminous Flux: 8000 lm (25 UV Finsens)
Luminous Efficacy: 16.0 lm/W
Colour Temperature & CRI: CCT: 5100K CRI: Ra25
Chromaticity Co-ordinates: CCx: 0.345 CCy: 0.385
Irradiance @ 50cm: UV-A: 17.0W/m² -- UV-B: 10.0W/m² -- UV-C: 0.23W/m²
Beam Distribution 120° to half peak intensity
Rated Lifetime: 1,000 hours
Warm-up & Re-strike Time: 3 minutes 5 minutes
Burning Position: Universal
Overall Length: 255 mm 10 inches
Factory: Eindhoven The Netherlands
Date of Manufacture: 1953 May Date Code: K8
Original Value: Hƒℓ 198 (1952) DM 135/- (1966)
References: 1) Philips Preisliste Spezialentladungslampen und Infrarotstrahler, 1966 Germany, May, p.6
2) Fifty Years of the High Pressure Mercury Vapour Lamp, W.Elenbaas, Philips Technical Review v.18 no.6 (1956/57) pp.167-172
3) The High Pressure Mecury Vapour Lamp, W.Elenbaas, publ. Philips Technical Library 1965, pp.216-220
4) Gas Discharge Lamps, J.Funke & P.J.Oranje, publ. Philips Technical Library 1951, pp.140-141
5) Philips Biosol Advert, De Ijmuider Courant 18th December 1952 p.9 (listing reduced sale price of the MLU 500W table lamp)
6) Philips Biosol Advert, Dagblad De Stem 19th March 1955 p.10 (listing MLU 500W and 250W models)
7) Philips Biosol Advert, Dagblad De Stem 5th November 1956 p.8 (listing MLU 500W and new 300W version)
8) Philips Biosol Advert, Nieuwe Leidische Courant 4th December 1956 p.8 (listing MLU 500W and new 300W version)