Depends on a lot of variables such as table size, type of lighting, etc. but if you are just looking for a number...then 50 inches from the bed of the table to the bottom of the light.
Critical Measurements
Floor to bottom of light – 78”
Distance from bottom of light to top of light – 7’ – 5” deep ; 9’- 8” deep
Distance between hang points – 4’
Mounting Tips
Use eye bolts or S-hooks attached firmly to a rigid point in ceiling (i.e. ceiling joist)
Space hanging points as close to 4’ as possible. Chain or cable may compensate for a few inches if necessary.
The aircraft cable hanging kit that is included adds 16”-18” to the distance that the light hangs from the ceiling.
It should be low enough so the light source doesn't shine directly in the eyes of a person waiting in their chair to shoot. Obviously there are a ton of variables but this is the key as far as I'm concerned. You can light the table surface well from just about any distance from 30 inches to ceiling mounted. Just keep the damned bare bulbs out of the eyes of the non shooters.