Light follows the Inverse Square Law as it gets dimmer the farther away it is from a point source. The simplified version of the formula is: intensity = source_strength / distance^2.
Also, you'll want to sum together the intensities of all lights illuminating a vertex. This would probably be easier if you looped over the lights for each vertex instead of the other way around.
Also, you'll want to sum together the intensities of all lights illuminating a vertex. This would probably be easier if you looped over the lights for each vertex instead of the other way around.