Laser Brightness Calculator

Laser brightness (radiance) describes how much luminous power a laser beam appears to emit relative to the human eye's sensitivity. It is calculated by multiplying the laser's optical power (in mW) by the eye's photopic luminosity function V(λ) at the laser's wavelength. A higher product means the beam appears brighter to an observer.

The human eye is most sensitive to green light around 555 nm, where V(λ) peaks at 1.0. Red light at 650 nm has a V(λ) of only about 0.107, meaning it appears roughly 9× dimmer than the same power of green light. This is purely a property of human vision, not the actual optical power.

V(λ) is the standardized response curve of the human eye under normal (photopic) lighting conditions. It ranges from 0 at the edges of the visible spectrum to 1.0 at 555 nm. Multiplying a laser's power by V(λ) at its wavelength gives a measure of perceived brightness.

Mesopic vision occurs in intermediate lighting conditions — neither fully bright (photopic) nor fully dark (scotopic). Under mesopic conditions, the eye's peak sensitivity shifts slightly toward shorter (bluer) wavelengths. Enable mesopic correction when evaluating laser visibility in dim environments such as twilight or indoor low-light settings. Note: this correction is experimental.

Not necessarily. A 5 mW green (532 nm) laser can appear significantly brighter than a 50 mW red (650 nm) laser due to the large difference in eye sensitivity between those wavelengths. The apparent brightness depends on both power and wavelength together.

The calculator supports wavelengths in the visible spectrum from 380 nm (violet) to 780 nm (deep red). Lasers outside this range (UV or infrared) are not visible to the human eye and cannot be meaningfully compared using V(λ).

The brightness ratio is Laser 1's apparent brightness divided by Laser 2's apparent brightness. A ratio above 1.0 means Laser 1 appears brighter; below 1.0 means Laser 2 appears brighter. For example, a ratio of 0.25 means Laser 1 appears four times dimmer than Laser 2.

This calculator is intended for comparing perceived brightness only, not for laser safety analysis. Laser safety depends on factors including beam divergence, exposure time, pulse characteristics, and wavelength-specific retinal absorption — which are beyond the scope of this tool. Always consult official laser safety standards (ANSI Z136, IEC 60825) for safety assessments.