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Average Illuminance Estimator

Check the average lux and foot-candles a fixture count delivers, and see how far it lands from the target for the space.

Inputs

Room

Sets the target used for the comparison. Use the override to work to your own spec.

Area actually served by these fixtures.

Switch to square metres for metric drawings.

Type a value to work to a client or code target instead of the default for the space.

Layout

Count every luminaire, including part rows.

Delivered lumens, not bare lamp lumens. Use the photometric file or the product label.

Losses

Share of fixture lumens that reaches the work plane. Typical interiors 0.6 to 0.8.

Light lost to dirt and ageing before the next cleaning or relamping.

Result

Average illuminance (imperial)
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Average illuminance
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Share of target
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Lumens needed for target
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Lumens per fixture for target
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Target illuminance
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Verdict
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What to check

  • Delivered lumens per fixture, not the bare lamp rating
  • Utilization factor for the ceiling cavity and room surfaces in this space
  • Fixture count actually installed, including part rows and dimmed zones

Related calculators

This calculator is a first-pass screen using the lumen method. Verify measured illuminance with a calibrated meter after installation, and confirm uniformity separately: an acceptable average can still hide dark bands between fixtures.

Saved calculations

Keep the assumptions with the result.

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