OP
Octopus
Maybe two rows of 5?
5 lights = 6 spaces between them!
Hum... Think fence panels and fence posts ..... The posts are the lights , and the panels are the spaces between them
So 5 lights would have 4 spaces,
Thus 3.5 minus 0.7 x 2 = 2.1 divided by 4 = 525 mm , which IMHO is far too close together unless you are lighting an operating theatre!