For a normal start you'll get the following lights in order:
5 min (plus class flag - usually F / red diamond on white - plus horn),
4 min (plus P flag - white rectangle on blue - plus horn),
1 min (P flag removed plus horn) and then
start (class flag removed plus horn).
For a 10 min start you'll get:-
10 min (you will also get the flashing amber beacon in front of the start box plus horn),
5 min (plus class flag plus horn),
4 min (plus P flag plus horn),
1 min (P flag removed plus horn) and then start (class flag removed plus horn).
Should it be necessary to shorten the race then the 10 min will be illuminated as well as the flashing amber beacon, (plus an S flag will also be displayed and 2 sound signals given on the horn).
The 10 and 5 minute lights with both be illuminated, an extra horn will sound and the class flag will stay down.
All 5 lights will be illuminated and two extra horns will sound.