I don't get why they didn't just either coat the whole lamp or leave the whole buldge on top clear rather than go through all that troble to make a clear stripe on the lamp.
The reason why they left the bulge uncoated is to avoid scratching off the phosphor when inserting the frame and creating dust in the lamp. But that uncoated area also allows uncorrected light to get out. The Sylvania's clearband was a rather ingenious system to keep the lamp's atmosphere dust-free, and at the same time prevent raw mercury light from being emitted!
Sylvania often had brilliant ideas and concepts like this. The grider frame is also their invention. If I'm not mistaken they are also the inventors of the /DX phosphor! It was first developed for the color cathode ray tubes they made back then. They tried the phosphor in a mercury lamp (probably for the giggles and laughs xD) and it was actually greatly superior to all other phosphors!
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Sylvania often had brilliant ideas and concepts like this. The grider frame is also their invention. If I'm not mistaken they are also the inventors of the /DX phosphor! It was first developed for the color cathode ray tubes they made back then. They tried the phosphor in a mercury lamp (probably for the giggles and laughs xD) and it was actually greatly superior to all other phosphors!