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This lamp was produced to assist in the marketing of the Sylvania Uniqtronic electronic ballast, created by Clalight of Israel in 1998. Almost from the beginning, Sylvania formed a partnership with Clalight to market these ballasts in the UK, as well as employing them in SLI luminaires.
A key feature of the Uniqtronic ballast is that while it drives the discharge itself at constant current, the cathodes are heated at constant voltage. Other ballasts use constant current for both. The Uniqtronic development is important for prolonging emitter life. As emitter and tungsten are evaporated over life, cathode weight decreases and resistance increases. Thus driving them at constant current causes them to be heated hotter and hotter as life proceeds, accelerating the emitter loss process and shortening the life. Driving at constant voltage however keeps the temperature much more constant as they age, and is the reason why the Uniqtronic ballast delivers much longer lamp life.
Another advantage of the Uniqtronic ballast is its ability to start the lamp even if one or both electrodes have physically broken. Other preheat ballasts are unable to start a lamp with a broken electrode. This lamp was made up with a specially broken electrode in order to show that the ballast can still strike the discharge (see photo).
Incidentally the first lamps for this test were made with no phosphor coating at all. However it was found that these were difficult to start on conventional magnetic gear, owing to the fact that the phosphor has some gettering effect and improves the lamp atmosphere. That is why this lamp was made only with clear ends around the cathodes.
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