IEC 62471 replaces the older photobiological labelling of lamps. It classifies a source by radiant power weighted against the eye’s response, then compares that value with the maximum exposure allowed for the worst case a user can realistically achieve. A 1W, 5000K downlight and a 10mW indicator LED can land in different groups even when both look equally bright.
The standard does not set a pass or fail limit. It sorts sources into risk groups so that the labelling, the cyrstal lens requirement and the warning signage follow the hazard rather than the wattage.
What the Standard Actually Measures
Three hazard mechanisms drive the classification: retinal thermal hazard, retinal blue light photochemical hazard, and infrared eye hazard. Each gets its own weighting curve defined in CIE 61472-1, applied to spectral radiance rather than to luminous flux.
| Hazard | Weighted quantity | Timescale used |
|---|---|---|
| Retinal thermal | Radiance weighted to 500nm-1000nm | 0.25s to 10s |
| Blue light photochemical | Blue radiance weighted at 435nm | 100s to 10,000s |
| Infrared | Radiance above 1400nm | 1000s |
Group boundaries use the worst case over the accessible beam. A source with a lens that concentrates light can reach a higher group than the bare die suggests, which is why photobiological testing is done on the finished optic, not on the chip on its own.
How the Four Risk Groups Are Set
Exempt (RG 0) means a source can be used indefinitely at the nominal distance without exceeding exposure limits. Low (RG 1) allows safe handling under warning labels but not under long staring. Moderate (RG 2) requires a warning and a limited exposure time. High (RG 3) needs engineering control and is normally excluded from public lighting.
The exposure limit falls as radiance rises for a fixed t. A source that sits at the RG 2 boundary at 200mm may drop to RG 1 at 500mm, because the accessible radiance drops with the square of the distance. That is why luminaire design and classification move together.
Why Pulse Width Changes a Result
IEC 62471 has no separate pulse rule, but a pulsed source is assessed at its peak radiance over the worst-case period. A pulse train at 100Hz with a 2ms duty cycle can still be Exempt if the average radiance stays under the limit, yet a strobe at 1kHz with the same average can be Moderate because the eye integrates over a longer window than the pulse period.
Drivers therefore need the photobiological result for the actual operating waveform, not for a CW equivalent. Dimming to 5% can move a fixture from Moderate to Exempt, which matters for staff corridors and school halls where the same fitting is used at full and at low output.
What Exempt Status Is Worth
Exempt does not mean blue light is absent. It means the dose a person could receive in normal use stays below the limit. A photography spot with a high radiance can still be Exempt under a short exposure and Moderate for a task light a technician reads a bench by for an hour.
RG 0 keeps the documentation simple wherever the label has to travel into a building file, particularly in schools, hospitals and food plants. Asking the manufacturer for the test report under IEC 62471 with the measurement distance and the duty cycle stated is faster than arguing from luminous flux.
Key Takeaways
- Classification follows spectral radiance and exposure time, not wattage or colour temperature alone.
- Test the finished optic under the real drive waveform, including the dimmest usable output.
- Distance and optics can shift a source between groups; the same die is not the same lamp.
- Ask for the test report, with distance and duty cycle, before trusting a published risk group.
- LED glossary: key terms from binning to lumen maintenance
- more optical safety and photometry notes in LED Academy
