What do all those LEDs mean on the arch pages?

The little LED-style images are intended to give a quick overview to all buildds of an arch. There a basically several types of status LEDs for the host itself and for the buildd in particular. More to come.
Here a some common meanings:

Host centric LEDs:
up
The host is up and running. It regulary updates its status. Everything is fine with the machine itself and its connectivity.
no response
The host exceeded its update interval by 1.25x the previous interval. It is now marked as not responding. This might be caused by a intermittent network problem for example.
down
The machine hasn't updated its status 4x in a row. It is marked as down now. The might be caused by a crash of the machine.
not participating
The buildd admin has decided to not participate with his machine. For whatever reason he has. Ask him. :-)

buildd centric LEDs:
idle
The buildd runs, but is idle.
building
The buildd runs and is building a package.
stopped
The buildd has been stopped by touching NO-DAEMON-PLEASE.
not running
The buildd does not run at all.
wait for key
The buildd has no access to wanna-build database and cannot automatically build packages therefore. But maybe some friendly mind runs some manuals builds on it to use its CPU for something useful.
need setup
Usually this occurs when a new buildd is added. But it might happen as well that this was caused by a serious chroot breakage and the admin needs to re-install the buildd environment.

The buildd host list is updated every 15 mins. You can see the time of last update on the buttom of the page.