Understand the physical quantity
What is Luminous Efficacy, Lumens and Power?
Photometry describes light as weighted for human vision, while radiometry describes physical radiant power. Flux, intensity, illuminance, luminance, irradiance, wavelength, frequency, and photon energy are related but distinct quantities.
Compare an entered measured or rated light-output relationship while avoiding unverified lamp or fixture assumptions.
The relationship
Keep quantity and basis explicit
Luminous efficacy η equals luminous flux Φ divided by input power P: η = Φ/P. Reverse modes solve flux or power from the same entered relationship.
See the workflow
What the calculator is doing
1Source or measured light2Apply geometry or spectrum3Photometric or radiant result
Worked context
Read the output in context
A source producing 1,600 lm from 14 W has a luminous efficacy of about 114.286 lm/W.
Interpret with care
Important boundary
Use consistently defined measured or rated quantities. The result does not infer wall-plug versus source efficacy, driver losses, optical losses, spectrum, color quality, lifetime, dimming, thermal behavior, or energy cost.
The result does not select a lighting standard, certify compliance, predict perception, or replace calibrated photometry and optical design.
Browse Light & radiation for related physical quantities.
Quick guide
How to use this calculator
- Choose the photometric, radiometric, or photon relationship first, then enter measurements using the stated geometry and unit basis.
- Keep luminous and radiant quantities separate. The calculator performs only the declared conversion, reverse solve, geometry, or measurement summary and exposes useful intermediate values.
- Use companion outputs to reconcile the scenario, then retain the stated instrument, distribution, spectrum, geometry, and environmental boundaries before applying the result.
Calculation method
How the luminous efficacy, lumens and power calculator works
Compare an entered measured or rated light-output relationship while avoiding unverified lamp or fixture assumptions.
Luminous efficacy η equals luminous flux Φ divided by input power P: η = Φ/P. Reverse modes solve flux or power from the same entered relationship.
Worked example
Luminous Efficacy, Lumens and Power example
A source producing 1,600 lm from 14 W has a luminous efficacy of about 114.286 lm/W.
Luminous efficacy η equals luminous flux Φ divided by input power P: η = Φ/P. Reverse modes solve flux or power from the same entered relationship.
Supported inputs
Precision and limits
Light and optics boundary
Use consistently defined measured or rated quantities. The result does not infer wall-plug versus source efficacy, driver losses, optical losses, spectrum, color quality, lifetime, dimming, thermal behavior, or energy cost.
Units and precision
Calculations normalize compatible units once, retain working precision, and round only for display. Very small and large nonzero values use scientific notation; displayed precision cannot exceed the entered measurements or source data.
Decision boundary
This calculator does not select a lighting standard, certify compliance, predict perception, or replace calibrated measurement, photometric distribution data, optical design, or safety assessment.
Privacy
Entered values and results stay in this browser and are not sent to analytics or third parties.
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