Evenly Lighting Your Space
Spacing your pendant lights evenly across the space they will light is often believed to provide the most even lighting. For example, a 60-inch-long island with three lights would have one light placed at the end of the counter on each side and the other placed in the middle.
This would mean 30 inches between each of the lights.
Spaced for Appearance
It is generally more attractive for pendant lights to be unevenly distributed across the space because this takes into account the pattern of light cast by the pendants. This does not mean, though, that they won't be evenly spaced from each other if you have more than two.
The spacing between them should always be the same to allow for symmetry.
Spacing pendant lights in a way that gives both quality lighting and aesthetically pleasing design provides the best of both worlds. Determining where the brightest light is cast from each pendant will allow you to ensure there aren't odd shadows or dark spots.
With the example of a 60" cabinet with three pendant lights, find the center point (30"). This is where you hang your first light.
Then find the halfway point from that center to the end of the counter. Your remaining two lights should be hung at this point on either side.
If you have more or less lights, find the center point and the halfway point on each end. Then evenly distribute your lights within that space.
An important note: Be sure to check for cabinet clearance before you hang your lights. You don't want to find that the doors hit the lights after you've gone to all the effort of hanging them.