---
title: "Radiometric → Photometric calculator — AperiOptic"
description: "Convert radiant flux (W) to luminous flux (lm) at wavelength λ. Free online optics calculator, with the formula and code snippets."
url: "https://aperioptic.com/calculators/radiometric-photometric"
---

# Radiometric → Photometric calculator

Convert radiant flux (W) to luminous flux (lm) at wavelength λ.

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

Formula: `Φv = 683 · V(λ) · Φe`

## Inputs

| Input | Parameter | Unit | Default |
| --- | --- | --- | --- |
| Radiant flux | `P` | W | 1 |
| λ | `lam` | nm | 555 |

## Result with the default inputs

- V(λ): 1
- Luminous flux: 683 lm

Open it with your own values: put each input in the address as a parameter, for example [`/calculators/radiometric-photometric?P=1`](https://aperioptic.com/calculators/radiometric-photometric?P=1). 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/radiometric-photometric (AperiOptic runs in the browser; free, no account). Every page of the site as Markdown: https://aperioptic.com/llms.txt