✨ Laser Brightness Calculator
Calculate a laser’s radiance (brightness) from its output power, beam diameter, and divergence angle.
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W
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mm
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mrad
What laser brightness (radiance) is
Radiance, often called brightness in laser terminology, describes how much optical power a source emits per unit area per unit solid angle. It’s a key figure of merit for comparing how tightly a laser’s energy is concentrated.
The formula
Radiance = P / (A × Ω), where P is the laser’s output power, A is the cross-sectional beam area (π(d/2)²), and Ω is the beam’s solid angle of divergence, approximated as π(θ/2)² for small full-angle divergence θ in radians.
This is a standard small-angle approximation used in laser and optics engineering references, valid for the narrow divergence angles typical of collimated laser beams.
Last reviewed August 2026