IEC 60825-1:2014/ISH1:2017

 IEC 2017
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
IEC 60825-1
Edition 3.0  2014-05
SAFETY OF LASER PRODUCTS –
Part 1: Equipment classification and requirements

INTERPRETATION SHEET 1
This interpretation sheet has been prepared by IEC technical committee 76: Optical radiation
safety and laser equipment.
The text of this interpretation sheet is based on the following documents:
FDIS Report on voting
76/587/FDIS 76/593/RVD
Full information on the voting for the approval of this interpretation sheet can be found in the
report on voting indicated in the above table.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
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Subclause 4.3 Classification rules
This subclause is clarified by the following:
Introduction
For some complex extended sources or irregular temporal emissions, the application of the
rules of subclause 4.3 may require clarification because of changes from IEC 60825-1:2007.
NOTE 1 For the purpose of this interpretation sheet, the abbreviation “AE” is used for “accessible emission”.
NOTE 2 The clarifications also apply in an equivalent way to MPE analysis, i.e. for Annex A.
ICS 13.110; 31.260
IEC 60825-1:2014-05/ISH1:2017-12(en-fr)

– 2 – IEC 60825-1:2014/ISH1:2017
 IEC 2017
1 Subclause 4.3 b) Radiation of multiple wavelengths
See IEC 60825-1:2014/ISH2.
2 Subclause 4.3 c) Radiation from extended sources
When using the default (simplified) evaluation method (subclause 5.4.2) for wavelengths
≥ 400 nm and < 1 400 nm, the angle of acceptance may be limited to 100 mrad for
determining the accessible emission to be compared against the accessible emission limit,
except in the wavelength range 400 nm to 600 nm for durations longer than 100 s where the
circular-cone angle of acceptance is not limited. When evaluating the emissions for
comparison to the Class 3B AELs, the angle of acceptance is not limited.
3 Subclause 4.3 d) Non-uniform, non-circular or multiple apparent sources
In subclause 4.3 d), for comparison with the thermal retinal limits, the requirement to vary the
angle of acceptance in each dimension might appear to contradict the labelling in Figure 1
and Figure 2 of subclause 5.4.3 where the field stop is labelled as circular.
Interpretation
A circular field stop is applicable for circularly symmetric images of the apparent source and
for this case is consistent with the procedure given in subclause 4.3 d). For images of the
apparent source that are not circularly symmetric, the simple example below clarifies the
application of subclause 4.3 d).
A circular field stop with an angular subtense equal to α is, however, applicable for non-
max
circularly symmetric profiles if the analysis performed according to subclause 4.3 d), following
variation of the angle of acceptance in each dimension, results in a solution which is equal to
α in both dimensions.
max
As a general principle, for whatever emission duration t the AEL is determined (such as the
pulse duration, the pulse group duration or the time base for averaging of the power), the
same emission duration t is also used to calculate α (t).
max
The following example demonstrates the method described in subclause 4.3 d) to analyse
irregular or complex images of a source. It is noted that the example is equivalent to the
second part of the example (“Additional Remarks”; 6 mrad spacing instead of 3 mrad) B.9.1 of
IEC TR 60825-14:2004 (however, for 6 mrad element spacing, the result in terms of which
grouping is critical was not correct). The source is a diode array (Figure 1). The task is to
determine the applicable AEL that limits the AE for Class 2. Each diode contributes a partial
accessible emission AE of 1 mW that passes through a 7 mm aperture stop at the distance
where the analysis is performed (i.e. a total power of 20 mW passes through the aperture
stop), and the emission is continuous wave. The analysis requires determination of the most
restrictive (maximum) ratio of AE over AEL by variation of the angle of acceptance in position
and size to achieve different fields of view.

 IEC 2017
α = γ
x1 x1
6 mrad
α = γ
x2 x2
2,8 mrad
α = γ
α = γ
y2 y2
y1 y1
2,2 mrad
IEC
Figure 1 – Image of a source pattern for the example of 20 emitters. Two possible
groupings are defined by the respective angle of acceptance γ and γ
x y
The analysis of a sub-group of sources is associated with a certain value of α for that group,
and a certain accessible emission associated with that sub-group. For instance α of a single
element equals (1,5 mrad + 2,2 mrad)/2 = 1,85 mrad so that the AEL = 1,23 mW. The
applicable AE = 1 mW and AE/AEL = 1 mW/1,23 mW = 0,8. For a vertical two-element group,
as shown in the figure with γ and γ , α = (2,8 + 2,2)/2 = 2,5 mrad so that AEL = 1,66 mW;
x1 y1
AE = 2 × 1 mW = 2 mW and AE/AEL = 1,2, which is more restrictive than AE/AEL for only one
element. For one row of 10 diodes α = (1,5 + 56,2)/2 = 28,9 mrad, AEL = 19,2 mW, the AE =
10 × 1 mW = 10 mW and AE/AEL = 0,5. Analysis of all possible groupings shows that the
vertical two-element group has the maximum AE/AEL and therefore is the solution of the
analysis. This means that the AEL of Class 2 is exceeded by a factor 1,2. Note that only a
portion of the power of 20 mW that passes through the 7 mm aperture stop is considered as
the AE (2 mW; as partial power within the angle of acceptance that is associated to the part of
the image with the maximum ratio of AE/AEL) that is compared against the AEL. The entire
array represents the highest ratio of AE/AEL in cases where the element spacing is
sufficiently close, e.g. when the contributions of extra elements to the AE are not dominated
by the increased AEL due to the larger subtended angle.
For pulsed emission, for the determination of α according to the above method (4.3 d)) where
the ratio of AE to AEL is maximized, requirement 3) of 4.3 f) is not applied, i.e. the AEL is
single
not reduced by C . Due to the dependence of α on emission duration t, the analysis of the
5 max
image of the apparent source may result in different values of α and of the partial accessible
emission, depending which emission duration is analysed for the requirements of 4.3 f). For
example, for emission durations shorter than 625 µs (α = 5 mrad), the maximum partial
max
array to consider in the image analysis is a vertical two element group.
Ref.: Classification of extended source products according to IEC 60825-1, K. Schulmeister,
ILSC 2015 Proceedings Paper, p 271 – 280; Download:
https://www.filesanywhere.com/fs/v.aspx?v=8b70698a595e75bcaa69
4 Subclause 4.3 f) 3) determination of α
For an analysis of pulsed emission, α , which is a function of time α (t), limits both the
max max
value of α for the determination of C (α) as well as the angle of acceptance γ for the
determination of the accessible emission (see 4.3 c) and d)) and Clause 3 of this
interpretation sheet; in this process, α (t) is determined for the same emission duration t
max
that is used to determine AEL(t) (i.e. the pulse duration or the pulse group duration for
α is
4.3 f) 3) and the averaging duration for 4.3 f) 2), respectively). However, the parameter
also used in subclause 4.3 f) 3) in the criteria which C is applied. For these criteria, the
parameter α is not limited in the same way as for the determination of C according to 4.3 d).
For the criterion “Unless α > 100 mrad”, the angular subtense of the apparent source α is not
restricted by α . For non-uniform (oblong, rectangular, or linear) sources, the inequality
max
needs to be satisfied by both angular dimensions of the source in order for C = 1 to apply.
0,5 mrad
– 4 – IEC 60825-1:2014/ISH1:2017
 IEC 2017
(α) and in the criteria “α ≤ 5 mrad”, “5 mrad < α ≤ α ”, and “α > α ”, the
To calculate T
2 max max
quantity α is limited to a maximum value of 100 mrad, equivalent to α that applies for
max
0,25 s emission duration and longer. For T and these inequalities, α is not limited to a value
of α (t) smaller than 100 mrad, and is therefore the same as the value that applies for the
max
determination of C for an emission duration of 0,25 s and longer. As is generally defined (see
subclause 4.3 d)) the arithmetic mean is applied to determine α, i.e. it is not necessary that
both dimensions satisfy the criterion “For α ≤ 5 mrad” independently.
For the determination of the applicable value of C in 4.3. f) 3) in an analysis of moving
apparent sources (originating from scanned emission when not accommodating to the pivot
point or vertex) the value of α in the respective inequalities relating to the choice of C in
4.3 f) 3) is determined for the stationary apparent source and the respective accommodation
condition that is analysed (such as accommodation to infinity).
5 Subclause 4.3 f) 3) groups of pulses with group duration longer than T
i
For non-uniform repetitive pulse patterns, i.e. groups of pulses (see Figure 2 for an example),
when α > 5 mrad and the duration of the group of pulses is longer than T , it is not clearly
i
stated how the thermal additivity expressed by requirement 3) of 4.3 f) is applied. For uniform
(i.e. constant peak power, duration and period) repetitive pulse trains, it is not necessary to
analyse the emission patterns in terms of groupings of pulses.
When individual pulses are close together, they are thermally grouped and thermally
represent one “effective” pulse so that C also (additionally to analysing the pulse train based
on the actual pulses and the average power) applies to these “effective” pulses, where N is
the number of pulse groups within T or within the time base, whichever is shorter.
t
group
Period of pulse within group
IEC
Figure 2 – Example of three groups of pulses (each group duration is longer than T )
i
where each group is considered as one “effective” pulse and C is applied to the AEL
that applies to the group duration, where C is determined with the number of pulse
groups within the evaluation duration (in the example of the figure N = 3)
For the analysis of pulse groups, the value of AEL is determined for the corresponding
single
pulse group duration t . For the determination of C , N is the number of pulse groups
group 5
within T or the time base, whichever is smaller. The respective value of C is applied to
2 5
to obtain AEL that limits the AE of the pulse groups, where AE is the sum of
AEL
single s.p.train
the energy of the pulses contained within the pulse group.
For the application of C to groups of pulses, the AEL(t ) applicable to the group needs to
5 group
be determined, as well as the energy per group (AE ). For groups of pulses where the
group
peak power of the pulses within the group varies, the group duration is not well defined. In
order to simplify the evaluation, t can be set equal to the integration duration for which
group
) was determined; it is not necessary to determine the group
the energy per group (i.e. AE
group
duration based on the FWHM criterion, which for groups of pulses with varying peak power is
not well defined. By setting t equal to the integration duration that is used to determine
group
AE (expressed as energy), the application of C to groups of pulses is a simple extension
group 5
of requirement 2) of 4.3 f) where the average power per group (equal to the energy within the
averaging duration t divided by the averaging duration) needs to be below the
average
AEL(t ) determined for the duration over which the power was averaged (AE and
average group
AEL(t ) expressed as power). As is common for the average power requirement, for
group
irregular pulse trains, the averaging duration window (when expressed as energy: the
Power
 IEC 2017
integration duration window) has to be varied in temporal position and duration (for instance,
if there are pulses with relatively low energy per pulse at the beginning or the end of the
group of pulses, integration durations that exclude those low-energy pulses need to be
considered also, not only the total group).
If individual pulses have sufficient temporal spacing (period larger than T , see below), as a
crit
simplified analysis, they need not be considered for an analysis as a pulse group under
4.3 f) 3). The temporal spacing that is necessary for pulses to only be considered separate
(and not analysed additionally as a group) depends on the angular subtense of the apparent
source and the duration of the pulses t within the group. Note that there can be several
pulse
levels of grouping, so that individual elements (with pulse duration t) within the group could
themselves be “effective pulses”, i.e. subgroups.
When the
– pulse group (t ) durations are between T and 0,25 s, and
group i
– the angular subtense of the apparent source is larger than 5 mrad, and
– the period of the pulses (see Figure 2) is shorter than a critical period T (if t < T ,
crit pulse i
the value of t is set equal to T ; further, for the determination of T , α is
pulse i crit max
, not the group duration) where:
determined for t
pulse
for α ≤ α : T = 2∙t where t is in seconds
max crit pulse pulse
0,5
for α > α : T = 0,01 α t where t is in seconds, and α is in mrad, not being
max crit pulse pulse
limited to α ,
max
then these pulses constitute a pulse group which is treated as effective pulses and C (where
N is the number of groups within the time base or T , whichever is shorter) is applied to the
AEL applicable to the pulse group. For the determination of AE, α is determined using the
max
duration of the evaluated pulse group, t . If above conditions are not fulfilled, then the
group
pulses within the group of pulses that is considered to be analysed as “effective pulse” need
not be grouped, i.e. the group of pulses does not need to be analysed as one “effective”
pulse.
Note that if multiple pulses occur within T , the rule as stated in 4.3 f) 3) applies in parallel,
i
i.e. they are counted as a single pulse to determine N and the energies of the individual
pulses that occur within T are added to be compared to the AEL of T where the
i s.p.train i
corresponding C for emission durations t ≤ T is applied.
5 i
6 Subclause 4.3 f) simplifications
a) Constant peak power but shorter pulses
Depending on the angular subtense of the apparent source, it can be the case that the
value of C is more restrictive for pulses with pulse durations less than T than for pulses
5 i
with durations longer than T which is against general biophysical principles for cases
i
where the peak power is the same.
Interpretation
For the case of varying pulse duration within a pulse train, if the accessible emission for
pulses longer than T is below the applicable AEL, then it can be assumed for the analysis
i
that pulses with durations less than T but with the same (or lower) peak power as the
i
longer pulses, are less critical. The rationale for this interpretation follows the principle
that when pulses have the same peak power, the shorter pulse cannot be more restrictive
than the longer one.
NOTE This interpretation can also be used to smooth the step function at T for the classification of products,
i
i.e. the classification of a product may be based on the assumption of pulse durations longer than T even if
i
they are shorter than T provided that the longer pulses satisfy the applicable AEL and the shorter pulses have
i
the same or lower peak power compared to the longer pulses.

– 6 – IEC 60825-1:2014/ISH1:2017
 IEC 2017
b) Larger image of apparent source
For emission durations exceeding T , due to the step-function of C at 5 mrad and at α ,
i 5 max
the AEL (as a function of C and C ) can be more restrictive for larger values of the
5 6
angular subtense of the apparent source as compared to smaller ones, which is contrary
to general biophysical principles.
Interpretation
When the class of a laser product is determined with the extended analysis (subclause
5.4.3) and the apparent source is larger than 5 mrad, the classification may be based on a
value of the angular subtense of the apparent source less than 5 mrad (resulting in a
smaller C but also larger C ). That is, when the AE is below the AEL for an assumed
6 5
smaller apparent source, the resulting class is applicable even though the image of the
apparent source is larger than 5 mrad. This also applies in an equivalent way to the step
function of C at α .
5 max
c) Using a square aperture stop
In some cases, such as 2D scanned laser beams, the use of a circular aperture stop to
determine the accessible emission creates very complex pulse patterns.
Interpretation
Analysis performed with a square aperture stop with 7 mm side length (for determination
of accessible emission and pulse duration) can be assumed to be equivalent to, or more
restrictive than, a circular aperture stop and is therefore a valid analysis.
d) Applicability of simplified default analysis
For pulse durations longer than T , the value of C is smaller (more restrictive) for angular
i 5
subtense values α larger than 5 mrad compared to α ≤ 5 mrad. The assumption of
α = 1,5 mrad is the basis of the simplified (default) evaluation. It is therefore not obvious if
the simplified (default) analysis still applies in terms of being a restrictive simplifying
analysis even for the case that the angular subtense of the apparent source is actually
larger than 5 mrad, where C < 1.
Interpretation
It is acceptable to make use of the simplified restrictive assumption of α = 1,5 mrad (C =
1, C = 1) even for the case that the angular subtense of the source is larger than 5 mrad.
This means it is not necessary to show that α < 5 mrad in order to apply C = 1 and C = 1
6 5
for the simplified (default) analysis, because overall this is a conservative simplification.
Note that the simplified default analysis implies that the determination of the accessible
emission is not limited by an angle of acceptance equal to α .
max
e) Determination of the most restrictive position
For the extended analysis, it is necessary to vary the position in the beam. For each
position in the beam, the accommodation is varied and the most restrictive image is
determined. For determining the most restrictive image (where the ratio AE/AEL is
maximum) at a given position, requirement 3) of 4.3 f) is not applied. Otherwise a blurred
(larger) image of the apparent source, resulting from variation of the accommodation,
could appear more restrictive, which is contrary to general biophysical principles. Once the
most restrictive image (and associated α) is identified for each position in the beam, all
three requirements 4.3 f) are applied to determine the most restrictive position (identifying
the position with the maximum ratio of AE/AEL).
f) Application of total-on-time-pulse method
For regular pulse trains, as well as for varying pulse durations and/or varying period of
pulses (but excluding strongly varying peak powers; see below), the total-on-time pulse
(TOTP) method (see also IEC 60825-1:2007, subclause 8.3 f) 3b)) may be used as
alternative to requirement 3) of 4.3 f), i.e. as alternative to the application of C to the
single pulse AEL, provided that α is determined for the TOTP (or using the worst case
max
value of 100 mrad). This is more restrictive than the rules of 4.3 f) because it is equivalent
to an unlimited C (C not limited to 0,2 or 0,4), and because the value of α is typically
5 5 max
larger for the TOTP as compared to the value applicable to the single pulse.

 IEC 2017
For total-on-time-pulse (TOTP) method the following applies, as reproduced from
IEC 60825-1:2007.
The AEL is determined by the duration of the TOTP, which is the sum of all pulse
durations within the emission duration or T , whichever is smaller. Pulses with durations
less than T are assigned pulse durations of T . If two or more pulses occur within a
i i
duration of T these pulse groups are assigned pulse durations of T . For comparison with
i i
the AEL for the corresponding duration, all individual pulse energies are added.
Note that the TOTP method in IEC 60825-1:2007 (incl. Corrigendum 1) was specified “For
varying pulse widths or varying pulse intervals” and did not refer to varying peak powers.
For the case of strongly varying peak powers, the TOTP method is not applicable, as
adding pulses to the pulse train with small peak powers and low contributing energy-per-
pulse values might increase the AEL (by increasing the total-on-time) more than this
increases the total energy, and thus would make the emission less critical as compared to
an emission based on the pulses with the large peak power only.
g) Varying peak power but constant pulse duration
For varying peak power but constant pulse durations (both less than or larger than T ),
i
requirement 3) of 4.3 f) can be applied by counting the pulses for the determination of N
based on the relative peak power, i.e. N is increased by 1,0 for each pulse with the
maximum peak power, and by a value of less than 1,0 for pulses with lower peak power,
such as for a pulse with 70 % peak power compared to the maximum peak power in the
pulse train, N is increased by 0,7. For this, based on the strong non-linearity of thermally
induced injury with temperature, it is justified not to count pulses with peak powers that
are more than a factor of 10 below the pulse with the maximum peak power (i.e. less than
10 % of the maximum peak power). Note that the resulting AEL is applied to the
s.p.train
pulse with the largest AE, i.e. the largest energy per pulse, and that the interpretation in
this paragraph applies only for the case of pulse trains with constant pulse durations.

 IEC 2017
COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE
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IEC 60825-1
Edition 3.0  2014-05
SÉCURITÉ DES APPAREILS À LASER –

Partie 1: Classification des matériels et exigences

FEUILLE D'INTERPR É T AT I O N 1

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Paragraphe 4.3 Règles de classification
Le présent paragraphe est clarifié par ce qui suit:
Introduction
Pour certaines sources étendues complexes ou émissions temporelles irrégulières,
l'application des règles du paragraphe 4.3 peut exiger d'être clarifiée compte tenu des
modificatio
...