Maximum Safe Exposure Duration
Calculate the maximum safe exposure time for a CW laser beam based on MPE 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.
Max Safe Exposure Time
770 ns
Limited by
Retina, thermal
| Limit | Max time | Aperture (mm) | Beam irradiance over it (W/m²) | Limit (J/m²) |
|---|---|---|---|---|
| Retina, thermal | 770 ns | 7.00 | 2598 | 2.00e-3 |
| Retina, photochemical (blue light) | 10.0 s | 7.00 | 2598 | 4365 |
Aperture, irradiance and limit are at the limit's max time (at 30 000 s if it isn't reached).
Exposure limits for the eye from ICNIRP 2013 (Health Phys. 105:271, Tables 3, 5, 7 and 8) for a point source (intrabeam viewing of a collimated beam, C_E = 1) and a CW exposure of 1 ns to 30 000 s. From 10 s on, the UV limits equal the EU limit values (Directive 2006/25/EC, Annex II, Table 2.3). The beam is a round Gaussian, centred, and its power is averaged over the limiting aperture: 7 mm for the retina; 1 mm, growing to 3.5 mm at 10 s, in the UV and from 1.4 µm to 100 µm; 11 mm beyond. A smaller pupil does not raise the limits. From 400 to 600 nm the thermal and the photochemical limits both apply; from 400 to 1400 nm the skin limit (twice it from 700 nm) protects the cornea and lens, which matters only from 1150 nm, where C_C raises the retinal limit. Not covered: pulses and extended sources. A beam under 1 mm (1/e diameter, d/√2 for the 1/e² d) is held to its peak on the cornea below 0.35 s (ICNIRP 2013 Table 5 note c).
Each limit as an irradiance, H(t)/t, and the beam irradiance over that limit's aperture. The beam is safe up to the first crossing.
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 point-source eye limits (180 nm – 1 mm, 1 ns – 30 ks) for a CW round TEM₀₀ beam centred on the averaging aperture (its peak if under 1 mm (1/e) on the cornea below 0.35 s, ICNIRP Table 5 note c). Not modelled: extended sources, pulses.
- 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, 7 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.