General service "A" bulbs (in recessed fixtures) provide wide light distribution. "R" and "PAR" bulbs concentrate light. Coverage per fixture is based on providing 15 to 25 footcandles of light. In rooms with darker color use higher wattages.
Number of fixtures needed in a given area: consult ALA showroom experts for manufacturer's literature. The "spacing ratio" number must be multiplied by the fixture's mounting height above the lighted area (tabletop, floor, counter, etc.) to give the maximum spacing for even illuminations.