Maximum Permissible Exposure (MPE)
Every eye exposure limit in force at a wavelength and exposure time, with the aperture it is averaged over. The lowest is the MPE.
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.
MPE, radiant exposure
6.36 J/m²
0.636 mJ/cm²
MPE, irradiance H/t
25.5 W/m²
2.55 mW/cm², for a constant exposure
Lowest limit
Retina, thermal
Averaged over 7.00 mm
Max power, narrow beam
980 µW
All of it inside the aperture; retina, thermal
| Limit at t | Aperture (mm) | H (J/m²) | H/t (W/m²) | Max power, narrow beam |
|---|---|---|---|---|
| Retina, thermal | 7.00 | 6.36 | 25.5 | 980 µW |
Every limit listed applies; the photochemical limit starts at 10 s. The max power is for a beam narrower than the aperture and holds for every exposure up to t (a limit can step down at a joint, e.g. at 10 s). Powers assume the beam fills the aperture; a beam under 1 mm (1/e) on the cornea below 0.35 s, or on the skin, is held to its peak instead (ICNIRP 2013 Table 5 note c). For a given beam size see exposure duration.
Each limit as a radiant exposure against the exposure time, 1 ns to 30 000 s.
Maximum permissible exposure of the eye from the ICNIRP 2013 limits (Health Phys. 105:271, Tables 3, 5 and 8) for a point source (intrabeam viewing of a collimated beam, C_E = 1) and one exposure of duration t: a CW beam on for t, or a single pulse. Each limit is a radiant exposure at the cornea, averaged over its aperture: 7 mm for the retina, 3.5 mm for the anterior eye, 1 mm growing to 3.5 mm at 10 s in the UV and from 1.4 µm to 100 µm, and 11 mm beyond. From 400 to 600 nm the thermal and photochemical limits both apply. From 1150 nm C_C raises the retinal limit, and towards 1400 nm the anterior-eye limit (twice the skin limit, from 700 nm; in the visible only for a large source) is the lower one; for a beam under 1 mm it compares the beam's peak (ICNIRP Table 7 note b). IEC 60825-1:2014 builds its emission limits on the same values, except in the UV (see MPE vs AEL). Not covered here: pulse trains (pulsed MPE), extended sources (extended source), the skin (skin MPE), and ICNIRP's advice to use the actual irradiance of beams under 1 mm.
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 point-source eye limits (180 nm – 1 mm, 1 ns – 30 ks) and their apertures, for one exposure of duration t; the power fills the aperture (a beam under 1 mm (1/e) on the cornea below 0.35 s is held to its peak, ICNIRP Table 5 note c). Not modelled: pulse trains, extended sources, skin.
- 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 3, 5 and 8. doi:10.1097/HP.0b013e3182983fd4
- EU Directive 2006/25/EC, Annex II, Table 2.3. Cross-check of the UV exposure limits from 10 s.