Duro-Test Mi-T Wattsaver

Developed in a joint project between Duro-Test and MIT, this is the first practical incandescent lamp to feature an infra-red reflective coating. Rated at just 65 Watts, it is intended to replace a conventional 100 Watt lamp.

The coating is of a Fabry-Perot design and comprises a thin layer of silver sandwiched between two layers of titanium dioxide. The coating is sufficiently thin as to be substantially transparent to visible light, but is an outstanding reflector of infrared. Its greenish colour results from a slight red absorption. The coating is not especially stable at high temperatures, hence the unusually large bulb diameter.

To faciliate alignment of the filament at the bulb centre a novel two-piece envelope is employed. The lower half is fabricated like a PAR reflector, bearing two ferrules and an exhaust tubulation. The filament mount is brazed into the ferrules to a high degree of precision. The upper hemisphere is then sealed to the lower by fusion of the glass rim.

Despite the impressive performance, by 1988 Duro-Test was forced to abandon its US $7 million investment due to insurmountable problems in tungsten metallurgy. It was crucial to employ a rigid filament which does not sag during life, since the smallest displacement results in a loss of the IR effect. Such a filament requires very high temperature recrystallisation prior to assembly, rendering it extremely brittle. Note the unusual end connections, in which it was even necessary to clamp the lead wires around the more elastic coiled-coil region of the filament. Sadly many lamps did not withstand the shocks encountered during transport, and like this one, arrived with a broken filament.
Manufacturer: Duro-Test Corporation
Lamp Power: 65 Watts
Lamp Voltage: 120 Volts
Lamp Current: 0.54 Amperes
Cap Type: E26s/38x45 Brass + vitrite
Bulb Type: G-95 G-30 in eighths/inch
Bulb Finish: IRC Coated Borosilicate glass
Filament Type: CC-8 Coiled-Coil Axial
Atmosphere: Krypton:Nitrogen Red P getter
Luminous Flux: 1400 lm
Luminous Efficacy: 21.5 lm/W
Beam Intensity: N/A
Beam Distribution: N/A
Colour Temperature & CRI: CCT: 2700K CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.460 CCy: 0.411
Rated Lifetime: 1000 hours  
Burning Position: Universal
Overall Length: 149 mm 5 ⅞ inches
Light Centre Length: 100 mm 4 inches
Factory: Clifton, N.J. U.S.A.
Date of Manufacture: c. 1980
Original / Present Value: