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Watts to Lux Estimate from Luminous Efficacy — result sheet
Estimate illuminance from electrical power, a supplied luminous efficacy, utilization factor, and illuminated area.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Nominal lumens = electrical watts × luminous efficacy; usable lumens = nominal lumens × utilization; average illuminance = usable lumens ÷ area in m².
Watts alone do not determine lux: electrical power must be paired with a luminous-efficacy assumption, and illuminance also depends on how much light reaches the target area. This estimate makes both inputs visible and reports nominal lumens, usable lumens, average lux, and foot-candles. It does not model spectrum, beam angle, distance, reflectance, glare, room geometry, fixture optics, dimming, or a photometric measurement.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Electrical power — W; minimum 1.0E-6; maximum 1000000000
- Luminous efficacy — lm/W; minimum 1.0E-6; maximum 683
- Illuminated area — m²; minimum 1.0E-6; maximum 1000000000
- Utilization reaching the area — %; minimum 0; maximum 100
Worked example
| Input | Value |
|---|---|
| Electrical power | 40 |
| Luminous efficacy | 100 |
| Illuminated area | 10 |
| Utilization reaching the area | 80 |
40 W at 100 lm/W gives 4,000 nominal lumens; with 80% utilization over 10 m² the estimate is 3,200 usable lumens, 320 lux, or about 29.73 foot-candles.
Assumptions and limits
- Electrical power is converted to nominal luminous flux using the entered efficacy in lumens per watt.
- The efficacy is an effective source/system value, not automatically the 683 lm/W monochromatic maximum.
- Utilization is a simple fraction of nominal lumens reaching the entered area.
- Illuminance is averaged uniformly over the area and one lux equals one lumen per square metre.
- No inverse-square point-source model, fixture distribution, spectral weighting, reflectance, or maintenance loss is inferred.
- The result is a planning estimate and not a lighting-code compliance, plant-lighting, or safety claim.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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