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Lighting Level Calculator

Average illuminance from the lumen method, the fixtures needed to hit a target footcandle level, and the resulting power density.

Inputs

Space and target

Floor area of the space being lit.

Illuminance you want at the work plane. IES guidance is roughly 5 fc for circulation, 20-30 for residential general, 50-75 for kitchens and workshops.

Fixtures

Delivered lumens of one fixture or lamp, from the product data.

Number of fixtures in the space.

Connected watts per fixture, used for the power density figure.

Room conditions

Share of lamp lumens reaching the work plane for the fixture, room shape, and finishes. 0.6-0.8 is typical; fixture photometrics give the real value.

Loss from dirt, lamp depreciation, and aging over the cleaning cycle. 0.7-0.9 typical.

Result

Average illuminance
16.8 fc
Average illuminance
181 lx
Lumens required at the lamps
10,714 lm
Even spacing per fixture
10.0 ft apart
Fixtures needed for the target
4
Connected load
30 W
Power density
0.15 W/sq ft

What to check

  • Delivered lumens per fixture from the product data, not the nominal lumen figure on the box.
  • Coefficient of utilization from fixture photometrics for your room dimensions and finishes; 0.6-0.8 is only a placeholder.
  • Maintenance factor for the cleaning cycle and lamp depreciation.
  • The target illuminance from the IES recommended practice for the task and occupant age, not a memory of a number.
  • Power density against any applicable energy code limit for the space type.

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Lumen-method estimate. It gives average illuminance only: it does not model glare, uniformity, shadowing, or task-level illuminance, and coefficient of utilization is a placeholder unless you have photometric data. Lighting design for safety-critical spaces belongs with a lighting professional.

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