Diffuse Reflection Hazard
Eye hazard of viewing a laser spot on a matte (Lambertian) surface: corneal irradiance, extended-source limit, diffuse hazard distance and OD, on the ICNIRP 2013 limits.
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.
Corneal irradiance at the viewer
0.637 W/m²
0.0637 mW/cm², from 0.500 W reflected
Apparent source size α
7.07 mrad
C_E = 4.71
Governing limit
Retina, thermal
Max irradiance 239 W/m²
Exposure / limit
2.67e-3× (within)
Diffuse hazard distance
1.86 mm
Set by: Anterior eye (skin limit, 2 × in the IR)
Optical density needed here
0.00
log₁₀ of the highest exposure / limit, at least 0
| Limit | Max irradiance (W/m²) | Exposure / limit | Hazard distance |
|---|---|---|---|
| Retina, thermal | 239 | 2.67e-3 | none |
| Anterior eye (skin limit, 2 × in the IR) | 19561 | 3.25e-5 | 1.86 mm |
The photochemical limit applies from 10 s; before that only the thermal limit does.
A matte (Lambertian) surface reflecting ρP gives ρP/(πr²) at distance r on its normal, once r is a few spot diameters. Nearer, the Gaussian spot gives ρP/(πr²) · x(1 − x eˣE₁(x)) with x = 8r²/d², which tends to the peak exitance 8ρP/(πd²) in contact. The eye focuses from 10 cm (ICNIRP 2013), so the retinal limits are assessed no nearer: closer up their ratio is the one at 10 cm, while the corneal limits keep rising. The spot is an extended source of angular size α = d₆₃/r, where d₆₃ = d/√2 is the diameter holding 63 % of the power (IEC 60825-1); this raises the retinal thermal limit through C_E (ICNIRP 2013, Table 2). The whole spot is counted (open field of view), so above α_max C_E = α²/(α_min α_max) (ICNIRP 2013, eqn 5) and close up the ratio stops rising. The blue-light limit counts the whole spot too, which errs high for spots larger than 11 mrad. Viewed off the normal the irradiance falls as cos θ. Specular (mirror) reflections are a direct beam: use the NOHD page.
Exposure over limit against viewing distance for each eye limit. The reflection is within the limits where every line is below the dashed limit line.
Model and references
Textbook approximation. A standard approximation from the literature (for example paraxial, plane-wave or Gaussian-beam), valid within the range the page states. About the tiers
Lambertian Gaussian spot: exact on-axis irradiance ρP/(πr²) · x(1 − x eˣE₁(x)), x = 8r²/d², tending to ρP/(πr²) far off; an extended source of α = d₆₃/r with ICNIRP 2013 C_E (open field of view, eqn 5), the retinal limits assessed no nearer than 10 cm (the eye's near point, ICNIRP p. 275); one exposure up to t. Errs high for blue light from spots over 11 mrad.
- 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. Table 2 and eqn 5 (C_E), Tables 5 and 8. doi:10.1097/HP.0b013e3182983fd4
- IEC 60825-1:2014, Safety of laser products – Part 1. Clause 3.10: angular subtense from the 63 % (1/e) diameter.
- ANSI Z136.1-2014, American National Standard for Safe Use of Lasers. Appendix B: nominal hazard zone, NOHD and optical density.