How many safety lights does a track need?

Start with the corners: that is where a driver needs the call earliest and where a flagman standing trackside is hardest to see. Four lights covers a typical short oval.

Then walk the track and look for the places where a driver cannot see the next light. A back straight with a crest, a corner with a bank of trees behind the flagstand, an infield that hides the tower. Those blind spots are where the next lights go.

Size the light to the viewing distance:

The system takes more lights later without changing what is already installed, so starting with the corners and adding is a reasonable plan.