Ed Hammer found that he was competing against himself when he was working with different lighting. He had the HID lamps which had a life of 20,000-24,000 hours and then there were fluorescent lights with a life of 10,000 hours. He decided that he needed to get the fluorescent lights up to a life of 20,000 hours to be competing with high pressure mercury.
The first step taken was in changing the electrode. He used an optimized overwind on the filament and extended the length of the filament. This created the opportunity to put more of the emission mix on the filaments as they were longer. The ratio held up to increase the life of the bulbs significantly. Normally 4mg of mix were used making the life 10,000 hours, so when 8mg of mix were used the life did increase to 20,000 hours. He said even an increase of 50% would have been nice, but he got it all the way to a 100% increase!
He then designed a stick cathode that could hold these 8mg of mix. From here, the life of the lamps went up to 20,000 hours. This was the birth of the fluorescent lamp with a life of of 20,000 hours in the U.S.! This same type is used today, but has been improved with electronic ballasts. These help to cut down on the sputtering of the filaments, and the life of the bulb can be extended even beyond 20,000 hours.
The emission mix on the filaments that is discussed is a triple carbonate ( made of barium, calcium, strontium carbonate). This is used in virtually all fluorescent lamps today. They are heated during the lamp creation process to turn to oxide, which enables them to emit electrons and function (CO2 breaks down). They must be heated in the process in order to emit the electrons. The electrons can then come out freely leading to: minimizes sputtering, longer life, cleaner ends, and better maintenance of the bulbs.
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Tags: fluorescent lamp, fluorescent lights, HID lamps, high pressure mercury, stick cathode
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