---
title: "Luminous Efficacy calculator — AperiOptic"
description: "Convert radiant power to luminous flux at a given wavelength (photopic). Free online optics calculator, with the formula and code snippets."
url: "https://aperioptic.com/calculators/luminous-efficacy"
---

# Luminous Efficacy calculator

Convert radiant power to luminous flux at a given wavelength (photopic).

Category: [Radiometry](https://aperioptic.com/calculators)

Formula: `Φv = 683 · V(λ) · Φe (lm/W)`

## Inputs

| Input | Parameter | Unit | Default |
| --- | --- | --- | --- |
| Wavelength | `lam` | nm | 555 |
| Radiant power | `P` | mW | 1 |

## Result with the default inputs

- V(λ): 1
- Luminous flux: 0.683 lm
- Efficacy: 683 lm/W

Open it with your own values: put each input in the address as a parameter, for example [`/calculators/luminous-efficacy?lam=555`](https://aperioptic.com/calculators/luminous-efficacy?lam=555). A unit other than the listed one goes in `<parameter>_unit`.

Read more: [Wikipedia: Luminous efficacy](https://en.wikipedia.org/wiki/Luminous_efficacy)

[All optics calculators](https://aperioptic.com/calculators)

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The interactive page: https://aperioptic.com/calculators/luminous-efficacy (AperiOptic runs in the browser; free, no account). Every page of the site as Markdown: https://aperioptic.com/llms.txt