FSO Eye Safety

How far from a free-space optical transmitter the beam is within every eye exposure limit, its laser class, and the margin at a distance you choose.

Model: Exact

Educational only — not compliance-grade

These pages implement the published exposure limits for the cases each one states, but they are educational tools: no laser safety officer has signed them off.

Do not use these results alone for PPE selection, NHZ / NOHD approval, controlled-area sign-off, enclosure/interlock approval, or formal classification.
Always verify against ANSI Z136.1, IEC 60825-1, your local procedures, and the responsible laser safety officer / CLSO.

Transmitter

Wavelength (nm)TX Power (mW)Beam Diameter at Aperture (mm, 1/e²)Beam Divergence (mrad, 1/e² full angle)Exposure Time (s)Check Distance (m)

NOHD

11.1 m

set by the Cornea (IR) limit

Laser class (IEC 60825-1)

Class 3R

CW, Conditions 1 and 3

Margin at 2.00 m

0.525×

exceeds the Cornea (IR) limit; P_max 52.5 mW

Beam Ø at 2.00 m

11.0 mm

1/e², a + rφ

Limits: ICNIRP 2013 eye exposure limits, the irradiance averaged over each limit's aperture (7 mm retinal, 3.5 mm or larger corneal).

Margin = largest power within every limit at that distance ÷ TX power; below 1 the exposure exceeds a limit.

NOHD: the distance where the Gaussian beam, growing as a + rφ, falls within every limit for exposures up to t.

Not modelled: atmospheric attenuation (which only shortens the NOHD), binoculars or telescopes, scintillation hot spots, pulsed modulation.

Model and references

Exact. The equations are exact within the stated assumptions, or are a standard's tabulated values. The results are as good as the inputs. About the tiers

ICNIRP 2013 eye limits for one CW exposure up to t; Gaussian beam averaged over each limit's aperture (its peak if under 1 mm (1/e) on the cornea below 0.35 s, ICNIRP Table 5 note c), growing as a + rφ; IEC 60825-1 class. Not modelled: atmosphere, optical aids, scintillation, pulsed modulation.

ICNIRP (2013). Guidelines on limits of exposure to laser radiation of wavelengths between 180 nm and 1,000 µm. Health Phys. 105(3), 271–295. Tables 2, 5 and 8. doi:10.1097/HP.0b013e3182983fd4
ANSI Z136.1-2014, American National Standard for Safe Use of Lasers. Appendix B: nominal hazard zone and NOHD.
IEC 60825-1:2014, Safety of laser products – Part 1: Equipment classification and requirements. Accessible emission limits and measurement conditions 1 and 3.

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