This question has been answered by Leslie Lyons, member of IEC TC 34 and 76 committees, and head of marketing at Bentham Instruments in Reading, UK.
It’s been ten years since photobiological safety and blue light hazard entered the lighting industry lexicon. Since the publication of EN 62471: Photobiological Safety of Lamps and Lamp Systems in 2008, standards have evolved.
The lighting industry has responded quickly to those changes, but the government and other agencies around the world that specify contracts and tenders have not. So don’t lose out by speaking the wrong standards language!
According to EN 62471, the risk group assessment of luminaires should be determined in application of the GLS condition, reporting (but not necessarily measuring) at the distance at which the luminaire produces an illuminance of 500lx.
This results in a risk group zero (RG0) classification for essentially all ‘white’ lighting products.
For the main part this chimed well with the desire for ‘low risk’ products. For the most risk-averse (and marketing departments), the ‘exempt’ nomenclature was adopted to avoid the unmentionable word ‘risk’, although qualified by a big fat zero.
This approach did however cause concerns in the interpretation of which light sources should be considered GLS and raised questions as to how to treat exposure at a distance closer than the 500lx. The way was paved for a new method for the assessment of lighting products.
Since 2012, a new approach, introduced by the IEC TC34 luminaires committee has been in place. According to the latest edition of the luminaire standard, EN 60598-1, implementing IEC TR 62778, assessment should be made to determine whether or not the luminaire under test exceeds the limits of EN 62471 blue light hazard risk group one (RG1) at a distance of 200mm.
Where this limit is exceeded, the RG1 hazard distance should be determined and reported on marking on the luminaire.
IEC TR 62778 does allow an RG0 assessment, but only at the 200mm measurement distance not 500lx as IEC 62471. As a result, few if any luminaires assessed under the new approach will receive the exempt risk group rubber stamp often requested by tenders and contracts.
Where an exempt risk group classification is called for, you could ask what standard is referred to. It is probable that the originator does not know what you are talking about and you will cause yourself more work.
The assessment result at 500lx can be conveniently calculated from your measurement results at 200mm. Simply multiply your blue light radiance result (W.m-2.sr-1) by the ratio (63695/ luminance (cd.m-2)). If the result is below 100 W.m-2.sr-1, then the assessment result is exempt at 500lx according to EN 62471.
You could be forgiven for missing this last step. Providing the luminaire correlated colour temperature (CCT) is less than 12500K (a fairly safe assumption here) then your source cannot produce a blue light radiance at 500lx to cause concern.
If you cannot beat them, join them and avoid the exempt risk group trap.
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