dont getter what it is

Outer Globe arc source metal hallide type lamp, at the top of the lamp there is that little button of stuff in a pan. What it called and what is its purpose? Bonus question, what is this outer globe filled with and what is the AU of it?

 

It's the getter. When building the lamp, they pump it down to remove as much of the air as possible, fill it, and seal it. Then they heat the getter (either by passing a current thru it or inductively) and it chemically combines with any remaining hydrogen. It's the same thing responsible for the shiny coating on the inside of radio tubes.

 

very good. I'll post a photo later. What does it mean if this explodes within the lamp?