Low Bay Lighting Calculator

Size LED low bay fixtures for spaces with 12–25 ft ceiling heights: workshops, small warehouses, gyms, and light manufacturing. Uses IES zonal cavity method.

Space & Task

Length 80 ft

Width 60 ft

Ceiling Height 18 ft

Work Plane Height 3 ft

Task / Application

Fixture Lumens 15000 lm

Fixture Wattage 100 W

Reflectance (ceiling/walls)

Light Loss Factor 0.80

Sizing Results

Floor area—

Room cavity ratio—

Required illuminance—

Total lumens required—

Fixtures needed—

Fixture spacing—

Total wattage—

Lighting power density—

ASHRAE 90.1 limit—

—

fixtures

Count needed

—

W/ft²

Power density

—

Total load

—

lm/W

System efficacy

Practical Notes

Low bay fixtures are mounted at modest heights, often below about 20 feet, in places such as workshops, retail stores, school gyms, and small warehouses. Above that height, high bay fixtures are normally used. Because the fixtures are nearer the floor, the beam spreads over a smaller area and the spacing between them must be closer.

The number of fixtures is worked out from the area, the target illuminance, and the lumens each fixture delivers, with allowances for how much light reaches the work plane and how the light output decreases over time. Typical targets range from about 100 to 300 lux for storage and general work areas to higher levels for detailed tasks.

Choose the beam distribution to suit the layout, with wide distributions for open floors and narrow ones for aisles with tall racking. Dimming and occupancy sensors save energy in areas that are not always in use. Check glare, since low mounted fixtures are more likely to be in the line of sight, and use shielded or diffused optics where needed.