MBTL PowerWhite Mercury Blended Lamp

This lamp is typical of the self ballasted mercury-blended types made by Philips during the 1960's and 1970's in the UK. The internal construction is substantially the same as the Dutch ML 160W.

The question is often asked as to why older mercury-blended lamps have round bulb shapes, whereas modern types share the same ellipsoidal glass as ordinary mercury lamps. There are two answers to this question.

When mercury blended lamps were first introduced, they were intended as direct replacements for incandescent lamps - hence it was advantageous to employ similarly shaped bulbs of the same dimensions to ensure maximum compatibility with existing luminaires. When fluorescent coatings were introduced to the range in the early 1960s, it was found that the ellipsoidal shape offered little benefit. It must be remembered that the primary reason for ellipsoidal bulbs is to achieve a uniform temperature over their surface, thus preventing overheating of the phosphor in certain areas. Phosphors lose efficacy rapidly if they are run at too high a temperature. Mercury blended lamps, of course, contain a tungsten ballast filament in addition to the arc tube, which produces a very great amount of heat. The bulb temperature is so high that the small benefit of the ellipsoidal shape is almost negligible.

Nevertheless, during the 1960s-1980s most manufacturers did migrate to the use of ellipsoidal bulbs for reasons of standardisation. That allowed a small cost reduction to be made by no longer having to change production equipment for the two different bulb shapes.
Manufacturer: Philips Electrical Ltd.
Lamp Power: 160 Watts
Lamp Current: 0.65 Amps
Lamp Voltage: 240/250 Volts
Cap: B22d/25x26 Nickel plated brass
Bulb Finish: Phosphor Coated MgFGeO : Mn
Bulb Type: A-90 Soda lime
Overall Length: 178 mm
Light Centre Length: N/A
Electrodes: Backwound thoriated Double carbonate emitter
Inner / Outer Atmosphere: Inner : Ar | Hg Outer: Nitrogen
Luminous Flux: 2,900 lm @ 100 hours 2,560 lm @ 3,000 hours
Luminous Efficacy: 18.1 lm/W @ 100 hours 16.0 lm/W @ 3,000 hours
Colour Temperature & CRI: CCT: CRI:
Chromaticity Co-ordinates: CCx: CCy:
Burning Position: Vertical cap up, or any if supply regulation is good
Rated Life: 6,000 hours (to 50% survival)
Warm Up / Re-strike Time:
Factory: Hamilton, United Kingdom
Date of Manufacture: September 1960
Original / Present Value: £2 8s 0d (1965) £28.52 (2002)
References: 1) Philips Lighting Catalogue UK, January 1965.