Sylvania Capsylite High Efficacy with Diode Rectifier

Soon after the first halogen retrofits for the ordinary A-line lamps were first marketed in America, GTE Sylvania raised the bar with the introduction of its ultra high efficacy Capsylite MB-19 series in 1986. Offered in ratings of 42W, 52W and 72W and intended to replace 60W, 75W and 100W incandescent lamps, they not only delivered a significant energy saving but also raised the lifetime to an impressive 3500 hours - while competitive halogen equivalents typically achieved only 2000h life and had somewhat lower efficacy.

The Sylvania achievement was made possible thanks to its use of small a rectifier diode inside the cap, which reduces the line voltage from 120V to about 85V by half-wave rectification with minimal losses. The diode can be seen in the X-Ray shadowgraph - it is located as far as possible from the heat of the filament. The lamp capitalises on the fact that lower voltage filaments can be driven at higher efficacy. For a given luminous flux, as voltage is reduced current must increase, and this necessitates a thicker tungsten wire. Thicker filaments take longer to evaporate to the point of failure, and part of this life increase can be offset by driving the filament harder. The resulting hotter operation leads to an increase in luminous efficacy.

The concept can only be applied successfully on 60Hz mains supplies. At 50Hz the diode results in unacceptable levels of flicker. Moreover the diode was also found to interfere with operation on dimmer switches, and this made Sylvania's lamps so unpopular that the design had to be abandoned in favour of a return to less-efficient 120V capsules. For many years later in the Americas, halogen lamps were conspicuously marketed as "Diode-Free" designs.
Manufacturer: Sylvania
Lamp Power: 72 Watts
Lamp Voltage: 120 Volts
Lamp Current: 0.6 Amperes
Cap Type: E26/25 Brass + vitrite
Bulb Type: MB-60 MB-19 in eighths/inch
Bulb Finish: Inside Frosted Borosilicate
Filament Type: CC-8 Axial Coiled Coil
Atmosphere: Bromine+Iodine in Kr Outer: Air
Luminous Flux: 1300 lm
Luminous Efficacy: 18.1 lm/W
Peak Intensity: N/A
Beam Distribution: N/A
Colour Temperature & CRI: CCT: 2900K CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.444 CCy: 0.406
Rated Lifetime: 3500 hours to 50% survival
Burning Position: Universal
Max. Overall Length: 111.1 mm 4 3/8 inches
Light Centre Length: 85.7 mm 3 3/8 inches
Factory: Winchester, KY U.S.A.
Date of Manufacture: 1989
Original / Present Value:
References: 1) GTE Sylvania Large Lamp Catalog USA, 1989.
2) Progress Report 1986, Lighting Design & Application, November 1986 pp.27-28.