Laser brightness – radiance – is power per unit area per unit solid angle. Because a laser beam is tiny and nearly parallel, even a milliwatt laser is far brighter than the Sun’s surface. Brightness is conserved by passive optics, so it limits how well a beam can be focused.
How to use the Laser Brightness Calculator
- Power P
- Wavelength λ
- Beam quality factor M²
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the power, wavelength and M² (1 for an ideal Gaussian beam). The comparison with the Sun uses its surface radiance of about 2 × 10⁷ W/(m²·sr).
Inputs explained
| Field | What to enter |
|---|---|
| Power P | Units: mW, W, kW |
| Wavelength λ | Units: nm, µm, mm, m, pm, Å |
| Beam quality factor M² | A number |
What each result means
- Radiance L = [Power P]÷([Wavelength λ]^2×[Beam quality factor M²]^2)
- Compared with the Sun’s surface = [Radiance L]÷2.0e7
Example values
How the main result changes when Power P changes and everything else stays at the example values above:
| Power P (mW) | Radiance L (W/(m²·sr)) |
|---|---|
| 2.5 | 7,300,143,106.1653 |
| 3.75 | 10,950,214,659.248 |
| 5 | 14,600,286,212.3307 |
| 6.25 | 18,250,357,765.4133 |
| 7.5 | 21,900,429,318.496 |
| 10 | 29,200,572,424.6613 |
Formula
L ≈ P / (λ²·M⁴) (W/(m²·sr))
Worked example
Inputs — Power P: 5 mW; Wavelength λ: 532 nm; Beam quality factor M²: 1.1.
Results — Radiance L = 14,600,286,212.33067 W/(m²·sr); Compared with the Sun's surface = 730.0143 ×.
Key terms
- Radiance
- Power per area per solid angle.
Frequently asked questions
Why is a laser pointer brighter than the Sun?
Its power is concentrated into a tiny area and solid angle.
Can lenses increase brightness?
No – passive optics cannot increase radiance.
How does M² affect brightness?
Radiance falls with M⁴ (M² in each direction).
Is a brighter laser more dangerous?
Yes – retinal hazard depends on how tightly the eye can focus it.