The various types of eye protection are broken down into classes in the Canadian Standards Association (CSA) standard Z94.3.1 "Selection, use, and care of protective eyewear".  Each class has a specific use that it has been designed for.  Common protectors for welding operations are listed below:

Class 2C - direct non-ventilated goggles with radiation protectionClass 3 - welding helmetsClass 4 - hand shieldsClass 5C - non-rigid helmets with radiation protectionClass 6B - faceshields with radiation protectionClass 7B - respirator facepiece with radiation protection

The following operations require full face protection from either a welding helmet or a hand shield:

arc welding,plasma arc cutting, gouging or welding, andair carbon arc cutting.

For gas cutting, welding, or brazing, the intensity of the light is much less than from arc welding, cutting or gouging processes.  Lighter shade filter lenses can be used with goggles in place of a helmet.