GEC MBF/U Truelite Mercury Fluorescent

The Truelite series of mercury discharge lamps from Osram-GEC was placed on the market in 1968, initially superseding only the low wattage versions but later being applied throughout the entire range. A new phosphor coating, europium activated yttrium vanadate, was the reason for re-branding mercury lamps under the Truelite name.

The magnesium fluoro-germanate phosphor, which had been the traditional mercury lamp phosphor until 1968, emits a deep red colour light at 658nm. However, the coating is itself slightly yellowish and this tends to absorb a certain amount of the blue radiation produced by the arc. Despite adding some red to the spectrum, the significant blue absorption results in a relative strengthening of the green 546nm mercury line. The net result is that although magnesium fluoro-germanate corrected lamps have a higher colour rendering index than previous phosphors, they impart an unpleasant greenish cast to their environment.

However the newer yttrium vanadate, a phosphor originally developed for the red component of colour television tube screens, is colourless. Its red emission peaking at 620nm is not so deep as with magnesium fluoro-germanate, but it is the crucial lack of absorption of the blue wavelengths which led to an overall improved colour appearance without the greenish cast. Europium-activated yttrium vanadate is the fluorescent material still employed today in modern lamps.

In addition to the new phosphor, Osram introduced a mica disc into the neck of >250W lamps at this time. It served to deflect heat and reduce cap temperatures thus ensuring that the capping cement held firm throughout lamp life.
Manufacturer: The General Electric Company of England Plc.
Lamp Power: 1000 Watts (for 220/240V single phase circuits)
Lamp Current: 7.75 Amps
Lamp Voltage: 145 Volts
Cap: E40s/45 nickel plated
Bulb Finish: Eu:YVO4 phosphor
Bulb Type: ED-165 Borosilicate
Overall Length: 400 10 mm
Light Centre Length: 260 mm
Electrodes: Backwound tungsten with triple carbonate emitter
Atmosphere: Inner : Argon | Hg Outer : Nitrogen
Luminous Flux: 54,000 lm @ 100 hours 51,000 lm @ 2,000 hrs
Luminous Efficacy: 54.0 lm/W @ 100 hours 51.0 lm/W @ 2,000 hrs
Colour Temperature & CRI: CCT: 4000K CRI: Ra 40-49
Chromaticity Co-ordinates: CCx: 0.380 CCy: 0.380
Burning Position Universal
Rated Life: 20,000hrs to 70% survival, 24,000hrs to 50% survival
Factory: Shaw, Oldham England
Date of Manufacture: August 1977
Original / Present Value: 14 0s 0d (1968) 146.94 (2001)
References: 1) Osram-GEC Mercury lamps brochure, 1968.
2) Osram-GEC Lamp Catalogue, UK, 1975, p.27