Maximum permissible exposure for show lasers and high-power moving lights
Inputs
Preset
Laser output
Wavelength (nm)Power at the aperture (mW)
Use measured power, not the nameplate value. Set a colour to 0 if it is not there.
Beam
mm
mrad
Beam movement
°
per s
A line drawn at 30 Hz passes each eye 60 times a second (there and back).
Light output
I know the
lx
m
lm
°
mm
Source
mm
K
The lit part of the front lens is what the eye sees as the source. If only part of the lens lights up, enter that smaller diameter.
Exposure
m
s
0.25 s is the blink reflex (accidental exposure). Use 10 s or more when people may look into the beam on purpose or cannot turn away.
Results
Exposure over distance
Exposure as a multiple of the limit
By distance
How this is calculated
A planning aid, not a safety approval. The results depend on the numbers you enter and on simplified beam models. A show with beams in the audience needs measured power and divergence, a laser safety officer and whatever your local rules require.
Limits: IEC 60825-1 eye MPE for 400 to 700 nm, small source: 18·t0.75 J/m² up to 10 s (25.5 W/m² = 2.55 mW/cm² at 0.25 s), then 10 W/m². From 10 s the photochemical limit for blue and green light is checked too, and the lower one counts. Colours are added together.
Beam: Gaussian, diameter² = aperture² + (divergence × distance)². Irradiance is averaged over a 7 mm pupil, so the result stops rising once the beam is smaller than the pupil.
Scanning: the beam crosses the eye at scan angle × passes per second × distance. Each pass is a pulse; the single pulse (with C5) and the average over the exposure time must both stay under the MPE. This assumes constant speed. Beams slow down at the turning points of a pattern and stand still if the scanner fails, so a scan-fail safeguard is needed before you rely on the scanned figure.
Lens: a diverging lens of power D in front of a beam of diameter a adds a divergence of about a × D. The value shown is the lens that brings the given distance down to the MPE.
Not covered: wavelengths outside 400 to 700 nm, pulsed (Q-switched) lasers, viewing through binoculars or camera lenses, reflections, skin limits.
Limits: ICNIRP 2013 / IEC 62471 for broadband light. Retinal thermal: radiance ≤ 20 000 / (α · t0.25) W/m²/sr up to 0.25 s, 28 000 / α after that (α = angle the source fills, at most 100 mrad). Radiance is averaged over 11 mrad (5 mrad below 0.25 s), and α is not taken smaller than that. Blue light: weighted radiance × time ≤ 10⁶ J/m²/sr, averaged over 11 mrad. The 0.25 s thermal limit is the border between risk groups 2 and 3, which is what a manufacturer's hazard distance refers to.
Source model: the front lens is treated as an evenly lit disc. Its luminance is peak intensity ÷ lens area and stays the same at every distance; only the angle it fills gets smaller. Close to the fixture the eye sees only a patch of the lens, so that angle is never larger than the beam angle. With a negative beam angle the beam narrows to a crossover in front of the fixture; the crossover then acts as the source, so it is smaller and brighter than the lens, and the exposure is highest around the crossover instead of at the lens. The hazard distance is the farthest point above the limit.
Spectrum: the radiant power and the blue-light share per lumen are estimated from a black body at the colour temperature you enter. Real LED, discharge and laser-phosphor engines differ by some tens of percent, and RGB laser engines can differ more.
Use the data sheet first: if the manufacturer gives a risk group and hazard distance (IEC 62471-5), that measured value beats this estimate.
Not covered: UV and infrared limits, heat on skin and materials close to the lens (see the fixture's minimum distance to lit objects).