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 standard low wattage versions but later being applied throughout the entire range.  A new kind of phosphor coating, europium activated yttrium vanadate, was the reason for re-branding all mercury products 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 powder coating is itself slightly yellowish and this tends to absorb a certain amount of the blue radiation produced by the arc tube.  Despite adding some red to the spectrum, the significant blue absorption results in an increase in intensity 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 illuminated 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, United Kingdom
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, 1985.