regulations | SAFE T Y
As a final note on the transfer of classifications, since primary light-source manufacturers have hitherto reported risk group
classifications of their products to IEC 62471,
the transfer of these classifications to luminaires may still be sought. In consideration
of the blue light hazard, classifications can
be transferred only if a measurement of true
radiance of the primary light source was
made. One should therefore consider the
diameter of the circular area evaluated by
each IEC 62471 risk group — RG0 (20-mm),
RG1 (11-mm), and RG2 (0.34-mm diameter).
If, in the luminaire, more than one emitter falls within the circular diameter corresponding to the reported classification,
transfer is not permitted.
Determination of dthr
Where a luminaire exceeds the limits of RG1
at 200 mm, one should determine at which
distance from the source the blue light RG1
limit radiance is found. For ease in evaluating this parameter, the blue light radiance
in 11-mrad FOV is considered through the
irradiance geometry: The threshold illuminance, Ethr, at the RG1 blue-light limit irradiance can then be computed. This has the
advantage of allowing the use of goniophotometric data (and the inverse square law) or
an illuminance meter to determine dthr, the
distance at which Ethr is found.
This does not take into account the fact
that the measurement should be evaluated
in an 11-mrad FOV. If the luminaire under
test subtends > 11 mrad at dthr, it follows
that emission from the source outside the
11-mrad FOV contributed to the measurement of illuminance used to find the location of Ethr, leading to an overestimate of dthr.
In certain circumstances this may not affect
applications, but it can impact the product
marketing since one will tend to select those
sources having a shorter dthr, with the perception of being safer.
Note that application of this technique is
currently provided for white light sources
only, since for colored light sources the use of
photometric detectors may give rise to a significant spectral mismatch error. Although
no specific guidance is given, it is reasonable to use goniophotometric or illuminance
meter data, provided that a comparative measurement against a spectroradiometer be
made to generate a correction factor.
Determination of dthr of extended sources
In the 2014 edition of IEC TR 62778, guidance
is provided in Annex D to address the case
where a source subtends > 11 mrad at the initial estimate of dthr, here labeled dN for clarity. Nominally applicable to arrays of LED
sources, the principles of Annex D can be
applied to any extended source.
The variation of blue light radiance
with distance is not easy to predict since it
results from averaging the luminous area
with the dark background over the mea-
surement field of view,
as demonstrated in
Fig. 3. It is therefore
on the spacing and
the shape of the lumi-
nous area of the source
with respect to the cir-
dN, one should evaluate whether or not
the luminous area of
the source extends
beyond the circular
area described by an
11-mrad FOV at dN,
of diameter 0.011∙dN.
Where the source
falls entirely with
this area, then dN=
Annex D approach this question from a different perspective, but due to ambiguity in
the definitions therein, this simple consideration is recommended.
The distance, d1, at which the Ethr of a single packaged LED occurs, should then be
determined. It is presumed that this will
be measured using an illuminance meter
FIG. 4. The upper image depicts the source extending beyond an 11-mrad FOV at dN,
demonstrating overestimation of threshold distance. At refined estimate, d1 (lower),
only one emitter falls in an 11-mrad FOV and d1= dthr.
TABLE 2. Possible IEC TR 62778 assessment results of
Assessment result Definition
RG0 Does not exceed limit of the blue light hazard exempt risk group
RG1 Does not exceed limit of the blue light hazard risk group one
dthr Distance from luminaire at which Ethr found
TABLE 1. Possible IEC TR 62778 assessment
results of primary light sources.
Assessment result Definition
RG0 unlimited Does not exceed limit of the blue light hazard
exempt risk group in any case†
RG1 unlimited Does not exceed limit of the blue light hazard
risk group one in any case†
Ethr Illuminance at which upper limit of RG1 found
†Provided operating conditions in the luminaire do not increase light emission