WELL !!!   I took the bulbs to the dual lamp rapid start ( High power factor) fixture and the rings are GONE!  There's a bit left on the bottom, but the bulbs now look as good as new. This is VERY interesting. 

Powell

Frequently the condensed mercury form dark bands, mainly after short heat surge on electrodes. Normally the electrde/lead in wires metal attract the mercury, but when it is heated, the mercury evaporate and condense on the cold glass. If the lamp does not warm up fully, the mercury stay there and form dark bands.
I think it is the sam mechanism, what make Alto's mercury starved after electrode overheat in cold lamp: The mercury is released from the amalgam, but as the glass is cold, it condense there and does not return. Then it is missing in the discharge, but i guess such state would be temporary - till the whole lamp fully warm up and the mercury evaporate from the glass.

The difference to sputtered electrodes is, then those dark bands disappear, as the mercury evaporate after warmup (but may return at cool down)

Quote from: Powell on May 26, 2011, 09:20:02 PM

WELL !!!   I took the bulbs to the dual lamp rapid start ( High power factor) fixture and the rings are GONE!  There's a bit left on the bottom, but the bulbs now look as good as new. This is VERY interesting. 

Powell

Frequently the condensed mercury form dark bands, mainly after short heat surge on electrodes. Normally the electrde/lead in wires metal attract the mercury, but when it is heated, the mercury evaporate and condense on the cold glass. If the lamp does not warm up fully, the mercury stay there and form dark bands.
I think it is the sam mechanism, what make Alto's mercury starved after electrode overheat in cold lamp: The mercury is released from the amalgam, but as the glass is cold, it condense there and does not return. Then it is missing in the discharge, but i guess such state would be temporary - till the whole lamp fully warm up and the mercury evaporate from the glass.

The difference to sputtered electrodes is, then those dark bands disappear, as the mercury evaporate after warmup (but may return at cool down)

If you overheat the cathodes on ALTO, it may reach full brightness after some time, or it may stay like that indefinitely. However, once you do it, it will go back to starved state after it is left off for a few hours.  It will never be the same.

I don't know if its specific to ALTOs. I just haven't tried it on anything else.

The strange thing is,  these bands looked like the aging bands you see and they were a light tan, and not mercury colored. Anyway, this is a CWX, and not as bright as other regular CW bulbs. And they are exceptionally reluctant to light with a LPF rapid start ballast. A friend of mine has 2 and often they won't light until he plays with them. I am just going to put a high power factor ballast in his fixture.

Powell