Info taken from
this page on Lamptech from
@James of course. Here we go:
1) Seriousness:
James writes "if measures are not taken to keep the sodium away from the seals, they will be attacked resulting in premature lamp failure". Alright, makes sense. But what kind of failure are we talking here? Will it just react and turn the glass black (I am assuming not), or will it crack and destroy the seal and make it leak? What actually happens when sodium attacks a seal?
2) Seal Design:
The seals are designed to remain hot while the lamp cools down so sodium doesn't condense on the seal. This was originally done (with some exceptions on question 3) with a magnesia bead fused to the end of the lead wires that were sheathed in inverted 2-ply glass tubing. That makes sense. But it also says that Philips later switched to a design that sheathed the wires in pure borate glass instead of 2-ply glass. Why wouldn't they do that from the start? That just seems like the simpler solution that is easy to think of. Also, is there any reason magnesia was chosen as opposed to alumina, or it it just convenience?
3) Glass types:
With the early SO dewar jacket lamps pictured on Lamptech, the ones made of soft glass had magnesia thermal mass beads and the ones using hard glass did not. Why does the type of glass used change whether or not it needs a thermal mass bead?
Thanks!
