MEI/H Coolseal Short Arc Metal Halide

GEC made its entry into the business of manufacturing MEI lamps in 1977 under the direction of engineer Angus Dixon, who made many contributions to the development of this light source. Also of particular value to GEC's MEI lamp business was the development of Dr. Alan Prest, which gave these lamps their "Coolseal" brand name.

MEI lamps dissipate immense power in a very small volume and it is easy for the quartz-to-molybdenum seals at either end of the arc tube to become overheated, oxidise, and then cause the lamp to fail by cracking the seals open. A great deal of infra-red energy is carried into the seals by the light pipe effect, in which infrared from the arc tube travels down each solid quartz seal as though it was a large optical fibre. This energy is concentrated at the end of the seal, inside the cap, where it can cause seal overheating and early failure.

Dr. Prest's ingenious solution was to etch the surface of the seal, thus destroying the light pipe effect and dissipating much of the infrared energy out the side of the lamp before it reaches the delicate seal ends which are exposed to air. The Coolseal principle was a most effective method of increasing MEI lamp life and it is still employed today by Osram, who inherited the rights to this patent after taking over the GEC's light sources business in 1988.

Lamp efficacy was further increased in the lower-wattage GEC lamps such as this 575W rating, by applying a heat-reflective layer of zirconium oxide around either end of the arc tube. This serves to increase the vapour pressure of metal halide salts in the arc, boosting colour rendering and luminous efficacy significantly.
Manufacturer: The General Electric Company of England PLC
Lamp Power: 575 Watts
Lamp Current: 7 Amps
Lamp Voltage: 95 Volts
Cap: SFc10.5-4
Bulb Finish: Frosted seals and zirconia-dipped arc tube ends
Bulb Type: BTT-21
Overall Length: 145 mm
Arc Gap: 13.6 mm
Electrodes: Solid Tungsten
Atmosphere: Argon
Luminous Flux: 49,000 lm
Luminous Efficacy: 85 lm/W
Colour Temperature & CRI: CCT : 5600K CRI : Ra 90-95
Chromaticity Co-ordinates: CCx : 0.335 CCy : 0.335
Rated Life: 750 hours
Factory: Shaw, Oldham England
Date of Manufacture: Circa 1988
Original / Present Value:
References: 1) Osram-GEC Lamp Catalogue, UK, 1985/86, p.234
2) GEC "MEI" Lamps brochure, c. 1980