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