How to Calculate Fluorescent Lights in a Shop

All lighting loads and lighting requirements fall under the regulation of the National Electrical Code, or NEC. Article 220 section 3 and Table 220-3(b) outline specific volt-ampere lighting requirements for all occupancies. Volt-amperes is the same calculation as wattage. All lights, including fluorescents, have ratings in wattage that is specified on the fixture. The wattage rating is equal to the fixture's overall light output.

• 1

  Measure the outside of the shop building's length and width. These measurements must be the exterior measurements of the building.

• 2

  Multiply the length times the width to find the shop's overall square footage.

• 3

  Calculate the required amount of lighting, in wattage, by multiplying the overall square footage times 2 watts. As an example, a shop of 1,000 square feet will require 2,000 watts of lighting.

• 4

  Divide the individual fluorescent light fixture rating by the overall requirement found in Step 3. As another example, the typical 4-foot two-bulb fluorescent light fixture has an average wattage output of 80 watts. Divide 2,000 watts by 80 watts and the resultant number of 4-foot two-bulb fixtures is equal to 25 fixtures evenly spaced throughout the shop.