Laser Eyewear Optical Density
Filter OD that keeps a CW beam within every eye exposure limit for exposures up to t, from its power, wavelength and diameter.
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.
The standards use 1/e values; 1/e² values are divided by √2. If unsure, pick 1/e²: it errs on the safe side.
Required OD
OD 3.71
Round up: eyewear of OD 4 or more
Governing limit
Retina, thermal
Largest power within the limits
98.0 µW
Including the safety factor 10.0
OD without the safety factor
OD 2.71
The safety factor adds up to 1.00
| Limit | Aperture at t (mm) | Max power ÷ safety factor | OD |
|---|---|---|---|
| Retina, thermal | 7.00 | 98.0 µW | 3.71 |
Each limit holds for every exposure up to t. The photochemical limit starts at 10 s; before that only the thermal limit applies.
Required OD against the exposure time
- Required OD
Optical density a filter needs so that a CW beam stays within every ICNIRP 2013 eye limit (Health Phys. 105:271) for exposures up to t: OD = log₁₀(P / P_max), where P_max is the largest power of this beam whose irradiance, averaged over each limit's aperture (7 mm for the retina, 3.5 mm for the anterior eye, 1 → 3.5 mm on the cornea in the UV and from 1.4 µm), stays within the limit. 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). A filter scales the power, not the beam profile, so this is the same as log₁₀(H/MPE) in ANSI Z136.1 (EN 207 instead rates eyewear by LB scale numbers from its own table of test power and energy densities). Typical exposure times: 0.25 s for visible beams (aversion response), 10 s for invisible ones, longer for staring. Not modelled: pulses (see pulsed MPE), EN 207 / EN 208 scale numbers, and whether the filter survives the beam.
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 (180 nm – 1 mm, exposures up to t) for a round 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); OD = log₁₀(P/P_max). Not modelled: pulses, EN 207 scale numbers, filter damage.
- 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 5 and 8. doi:10.1097/HP.0b013e3182983fd4
- ANSI Z136.1-2014, American National Standard for Safe Use of Lasers. Appendix B: optical density of protective eyewear.
- EN 207:2017. Personal eye-protection equipment – Filters and eye-protectors against laser radiation (laser eye-protectors).