Yeah that's an older type of surge protection. Most newer photocontrols use MOV's.

What's this type called? What's the difference between this and MOVs?

It's a type of spark gap arrester. Intermatic still uses this type of surge protection in their "low cost" series of photocontrols, the ones that have the printed colored band all over the outside. I couldn't tell you what the exact differences are though. I'd have to do research.

Ah I see. So thise type of surge protection isn't as effective as MOVs?

Still providing protection even tho not lighting, as there is a connection to utility line.

Yeah it's a nice open cap. My other open caps don't have surge protection. The cover comes off this unit really easy too. It can easily be turned into a shorting cap.

I've got one of these, odly mine has everything inside except the small contact piece that moves.

Hmm weird. I wonder why they'd waste all those parts. I guess the amount of open caps they produce is probably small.