Thermal vs Photochemical Retinal Limits
The two ICNIRP 2013 retinal limits at 400–600 nm against exposure time, for a point or an extended source, and the time from which the blue-light (photochemical) limit governs.
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.
Thermal limit at t
1000 J/m²
10.0 W/m², 385 µW through 7 mm
Photochemical limit at t
100 J/m²
1.00 W/m², 38.5 µW through 7 mm
Governing at t
Retina, photochemical (blue light)
Photochemical governs from
10.0 s
C_B = 1.00, C_E = 1.00 at t, T₂ = 10.0 s.
Retinal limits from ICNIRP 2013 (Health Phys. 105:271, Tables 2–5), as corneal radiant exposure averaged over 7 mm. Thermal: 18 C_E t^0.75 J/m² (2 mJ/m² below 5 µs), and from T₂ a constant irradiance; a point source (α ≤ 1.5 mrad) has 10 W/m² from 10 s. Photochemical (blue light), from 10 s: 100 C_B J/m² to 100 s, then C_B W/m², with C_B = 1 up to 450 nm and 10^(0.02(λ − 450)) above; C_E does not raise it. Both apply and the lower one governs. For a point source the photochemical limit takes over at ICNIRP's T₁: 10 s below 450 nm, 10 C_B s up to 500 nm; above 500 nm the 10 W/m² thermal limit stays lower. A larger source raises only the thermal limit, so the photochemical one takes over sooner and at longer wavelengths. For an extended source the photochemical exposure is measured over an 11 mrad field of view (to 100 s), which this page does not do.
Both retinal limits as irradiance at the cornea against exposure time; the lower curve governs.
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 retinal thermal (with C_E and T₂) and photochemical limits, 400–600 nm, as corneal exposure over 7 mm. The photochemical field of view of an extended source is not applied.
- 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, 3, 4 and 5. doi:10.1097/HP.0b013e3182983fd4