Eficiência luminosa
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
The luminous efficiency calculator (lm/W) converts the light flux of a source into watts, based on the efficiency of energy-to-visible-light conversion. It uses the formula: Luminous Efficacy = Luminous Flux (lumens) / Electrical Power (watts). This tool helps compare lighting devices like LEDs or bulbs, enabling more energy-efficient choices.
To use it, input the light flux in lumens and the power consumption in watts. The result shows how many lumens the source produces per watt. Higher values indicate greater efficiency. For instance, an LED emitting 1000 lm with 10 W has 100 lm/W, while an incandescent bulb achieving the same 1000 lm might require 50 W (20 lm/W).
Note that luminous efficacy does not reflect light quality. High-efficiency sources may emit light spectra unsuitable for specific applications. The calculator also ignores factors like lifespan or initial cost. Use it as a technical reference, not the sole decision-making criterion.
Frequently asked questions
What does lm/W mean?
lm/W (lumens per watt) measures light source efficiency, showing how many lumens are produced per watt of energy consumed. Higher values indicate greater efficiency.
How does the calculator use the formula?
It divides luminous flux (lumens) by electrical power (watts). Example: 800 lm / 10 W = 80 lm/W.
Is the calculator valid for all lamp types?
Yes, the formula works for LEDs, fluorescents, incandescents, and others as long as lumens and watts are accurately provided.
Does luminous efficacy affect energy bills?
Yes. Higher efficacy sources (more lumens per watt) reduce energy consumption for the same light output, lowering costs.