Square canopy
Size
5 ft by 5 ft (152 by 152 cm) is about 25 sq ft
Even hang
a centered HID or a small grid of lamps covers this shape cleanly
Walk space
keep a path outside the square so you do not shade the edge plants
Reflectors
walls or sheeting around the square bounce stray light back onto the canopy
Short rectangle
Size
6 ft by 4 ft (183 by 122 cm) uses the same lighting budget as the square
Movers
HPS lamps on a rail that travels about 1 ft (30 cm) even out hot spots
Lamp count
three or four 400 W lamps fit this footprint well
Why move
one fixed point leaves corners dim on a 6 by 4 bed
Long narrow rectangle
Size
12 ft by 2 ft (366 by 61 cm) is a hallway-style canopy
Fixed lamps
three or four 400 W lamps spaced along the run
Movers
two 600 W or 750 W lamps, each traveling about 6 ft (182 cm)
Use case
closets and alcoves that are long and thin
Circle canopy
Size
about 5.5 ft (168 cm) across, the footprint of many hard plastic kiddie pools
Lamps
any HPS mix that covers the disk without lighting empty floor
Edge plants
the rim is farthest from a center lamp, so check intensity there
Tray bonus
a round pool liner also catches runoff
Pick a shape for the room you have
Match the walls
do not force a square into a 2 ft closet
Cover every plant
unused floor at the ends of a rectangle is wasted watts
Movers vs more lamps
motion spreads one lamp; extra lamps add more points of light
Same watts, same potential
shape is a coverage problem, not a yield formula by itself