---
title: "Point Source Irradiance calculator — AperiOptic"
description: "Solid angle and irradiance on a detector from an isotropic point source. Free online optics calculator, with the formula and code snippets."
url: "https://aperioptic.com/calculators/point-source-irradiance"
---

# Point Source Irradiance calculator

Solid angle and irradiance on a detector from an isotropic point source.

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

Formula: `E = P/(4πd²) · Ω = 2π(1 − d/√(d² + A/π)) ≈ A/d² · Pdet = P·Ω/(4π)`

## Inputs

| Input | Parameter | Unit | Default |
| --- | --- | --- | --- |
| Source power | `P` | W | 1 |
| Distance | `d` | m | 1 |
| Det. area | `A` | mm² | 10 |

## Result with the default inputs

- Irradiance: 0.0796 W/m²
- Solid angle: 1.0000e-5 sr
- Power on det: 7.9577e-7 W

Open it with your own values: put each input in the address as a parameter, for example [`/calculators/point-source-irradiance?P=1`](https://aperioptic.com/calculators/point-source-irradiance?P=1). A unit other than the listed one goes in `<parameter>_unit`.

Read more: [Wikipedia: Inverse-square law](https://en.wikipedia.org/wiki/Inverse-square_law)

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

---

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