During the 1970s, energy crises lamp makers scrambled to develop products that would be more energy efficient. One manufacturer, Duro-Test, began working with researchers at the Massachusetts Institute of Technology (MIT) on an improved version of the ordinary incandescent lamp. The resulting product was called the "MI-T-Wattsaver" and was produced by the company from 1981 through 1989.
The basic concept seemed simple. The hotter a tungsten filament operates, the more efficient it becomes. Most of the energy emitted by the filament is in the form of invisible infrared rays that we feel as heat. If some of that heat could be directed back at the filament to raise its temperature, the lamp would give more light with no additional electricity needed. The researchers at Duro-Test and MIT called this concept a heat-mirror. They developed a special coating that would allow visible light to pass while reflecting infrared back to the filament, and put the coating on the inside of the glass bulb.
The concept worked but problems emerged. Tests showed that the coating aged with use, reducing the amount of heat reflected to the filament. The lamp was also difficult to make since the coating needed to be precisely applied and the filament needed to be mounted exactly in the center of the round bulb. As the price of compact fluorescent lamps fell in the late 1980s, Duro-Test decided to discontinue the MI-T-Wattsaver. The heat-mirror concept continues in use today in some tungsten-halogen lamps though.
The lamp seen here is a prototype sent to the U.S. Department of Energy for testing and evaluation in 1981.
Lamp characteristics: The piece has two sections-the lamp itself and a base adapter. The lamp has a brass bi-pin base (1/2" pin spacing with exhaust tube in between). Tungsten filament (broken) in CC-8 configuration with crimp connectors. A metal disc inside bottom of envelope may serve as a heat shield (the base pins pass through this disc). Tipless, G-24 glass envelope made in two halves. Both halves have an interior coating of infrared-reflecting film. The base adapter has a brass medium-screw shell, the insulator is part of a three-piece plastic skirt. Twist-lock receptacle on top connects to lamp.
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