For laser wavelengths in the range 320.5 to 4000 nm, the transmission window of Silica, measurement conditions for classification take into account the hazard associated with the use of optical viewing aids. The new EN60825-1:2001 specifies different conditions for 'naked eye' exposure, microscopes/eye loupes and telescopes/binoculars. In the retinal hazard range (400 - 1400 nm) the three measurement conditions are:

1. the maximum output collected through a 50 mm aperture at 2 m must not exceed the appropriate Accessible Emission Limit. This measurement simulates the output that could enter the eye if a x7 telescope or binocular of 50mm acceptance aperture is used to view the laser output at this distance.
2. the maximum output collected through a 7 mm aperture at 14 mm must not exceed the appropriate AEL. This measurement simulates the output that could enter the eye if a magnifier or eye loupe is used close to the laser source. (Note: A 14 mm measurement distance applies for the case of a 'point' source. For extended sources a somewhat greater distance is specified).
3. For Class 1 and 2 only, the AEL must not be exceeded through a 7 mm aperture placed 100 mm distance from the 'apparent source'. This measurement simulates 'worst case' naked eye viewing, 100 mm being taken as the shortest distance of normal accommodation.

For Class 1M and 2M laser products, defined as safe only for unaided viewing, only condition (3) need be satisfied, with the caveat that the output collected under measurement conditions (1) and (2) must not exceed the Class 3B AEL. Readers should also note that although these measurements for classification are designed to be performed by the manufacturers of lasers, they can usefully be exploited by users wishing to assess situations where optical viewing aids may be used.