In the Ex-mark why is op-is Important?
Simply put, any ignition risk in a hazardous area application means there is a danger of an explosion which could lead to loss of life or catastrophic damage. While the likelihood of an ignition due to optical radiation may be small, using luminaires which do not carry the op-is mark is a risk; the luminaires will not have been tested or certified to ensure that optical radiation does not present a danger. Is it a risk worth taking?
Of course, the inclusion of op-is represents a fairly recent update to the ATEX directive, meaning any luminaires installed prior to this will not carry the op-is mark. Replacing an entire installation of older luminaires in order to comply may be unrealistic, but the new standards should be taken into account for any new luminaires installed.