IEC 60825-1:2007/ISH2:2011

TC 76/Publication IEC 60825-1 (2007), second edition/I-SH 02

SAFETY OF LASER PRODUCTS –
Part 1: Equipment classification and requirements

INTERPRETATION SHEET 2
This interpretation sheet has been prepared by technical committee 76: Optical radiation
safety and laser equipment.
The text of this interpretation sheet is based on the following documents:
ISH Report on voting
76/437/ISH 76/440/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.
___________
Subclause 8.3 f 3)
This subclause is clarified by the following:
Introduction
For pulse durations shorter than 1 ns, the application of the criterion given in 8.3 f 3) a) (the
-0,25
„N criterion“) produces overly-restrictive results when compared to the TOTP criterion 8.3
f 3) b).
NOTE This Interpretation Sheet also applies to MPE analyses (subclause A.3 c)).
Interpretation
In the wavelength range of 400 nm to 1 400 nm, the TOTP criterion (8.3 f 3) b)) can be
applied for the case of pulse trains with pulses of the same energy and duration.
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NOTE 1 If the “N criterion” is applied, it would have to be adopted as follows so that it results in equivalent
evaluations as the TOTP criterion:
Pulses with durations less than T are assigned pulse durations of T . If two or more pulses occur within a duration

i i
of T , these pulse groups are assigned a pulse duration of T . The reduction factor C is applied to the AEL that is
i i 5
applicable for T (i.e. C · AEL(T )). If one pulse occurs within T , the energy of that pulse is compared with the

i 5 i i
reduced AEL, i.e. with C · AEL(T )). If more than one pulse occurs within T , the sum of the energies of these

5 i i
pulses is compared with the reduced AEL.
NOTE 2 For the heading of 8.3 f 3) b)), instead of “for varying pulse widths or varying pulse durations” the
intended wording was “for varying pulse widths or varying pulse intervals“ as corrected in Corrigendum 1”.
Rationale
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For constant pulse durations and energies, the two criteria (the N and the TOTP criterion)
should be, as a general principle, equivalent for all pulse durations, as both reflect the same
January 2011 ICS 13.110; 31.260

thermal additivity of multiple pulse exposures and constant pulse trains are a special case of
non-constant pulse trains.
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For pulse durations longer than T , the TOTP and the N criteria, as given in IEC 60825-
i
1:2077, do produce mathematically identical evaluations. For pulse trains where individual
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pulse durations are shorter than 1 ns, because the N criterion is applied in IEC 60825-1

to the AEL for the single pulse (which for pulse durations less than 1 ns is smaller than the
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AEL for T of 18 µs or 50 µs), the N criterion and the TOTP criterion produce different
i
results. Since both rules are intended to reflect thermal additivity of pulses, the TOTP is the
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criterion equivalent with
more general criterion. Criteria that would make the current N
the TOTP criterion are outlined in NOTE 1 above.
This instruction will remain valid until a new version of IEC 60825-1 is published.

January 2011 ICS 13.110; 31.260

CE 76/Publication CEI 60825-1 (2007), deuxième édition/I-SH 02

SÉCURITÉ DES APPAREILS À LASER –

Partie 1: Classification des matériels et exigences

FEUILLE D'INTERPRÉTATION 2
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