An emission indicator [1040.10(f)(5)] is required on Class II, IIIa, IIIb, and IV laser systems. The indicator can be visible or audible. On Class IIIb and IV laser systems the indication must precede emission by a length of time sufficient to allow users and others in the area to recognize that the product has been energized so they can avoid expo-sure. Depending on the action required and the level of laser radiation involved, the time needed can vary considerably; typical values are in the range of 2 to 20 seconds. Emission indicators must be duplicated on lasers (heads) and operation controls if they are capable of being separated by greater than 2 meters.