The Interior Tool will calculate the number of luminaires needed to meet an average illuminance across the workplane for an enclosed rectangular room using the principals of the lumen method. You can also use the Interior tool to determine the illuminance achieved by a specified lighting power density or luminaire quantity.

  • Load multiple IES files into the tool
  • Isometric, elevation and reflected ceiling views
  • Learn about how the Lumen Method Works
  • Quickly calculate simple rooms


The Visual Interior Tool is designed to perform lumen method calculations on a rectangular room. The lumen method determines average illuminance achieved on the workplane using a derived property of luminaire photometrics and room geometry called the coefficient of utilization. The lumen method makes the following assumptions

  • Luminaires are spaced uniformly
  • Room is empty
  • Surfaces are diffuse
  • Surfaces have neutral color

Because the lumen method provides an average illuminance, point values for calculations might vary considerably. Please use the professional edition of Visual for full lighting analysis.

Values calculated during the zonal cavity method are shown in the collapsible panel below the Display settings. These values are provided to help those curious about how the zonal cavity method works see the intermediary values that must be calculated in order to perform the calculation. For more information on the lumen method / zonal cavity method consult the IESNA Lighting Handbook.

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