Cut-Out (Or Circuit-Interrupting) Lampholder

Posting this one to show something from a discussion in the off-topic section of the forums here...
Here I've taken apart... A cut-out lampholder (sometimes also called a circuit-lnterrupting lampholder)

Note how there's 3 wires going in, and an extra piece of metal on one side.
The white wire is your neutral-from mains, and the yellow (in this case) connects to the white/neutral of the ballast.
Red is the red from the ballast.

The idea behind these is when you remove the lamp, it breaks contact between the 2 metal parts, cutting power to the ballast (hence the name "cut-out lampholder").

These are fairly common on 1-lamp fixtures with LPF magnetic ballasts.
Personally I hate the things because they suck, eventually they get to the point where they stop making good contact, and thus the fixture fails to light.
F40 LPF ballasts suck too since they're not the most reliable things for fireing up a lamp anyway.

"Fixing" one of these is simple enough, simply connect the 2 wires (white & yellow here, most of the time 2 whites) to the neutral & ballast white.

The fixture this was in, I converted from LPF F40T12 to Electronic F32T8. (a good upgrade)