There are two common styles of welding helmets, a passive and an auto-darkening variable shade. A passive helmet has a dark tinted lens, typically a shade #10. When the helmet is in the down position, you will see through the dark lens. The lens will not switch from a light state to a darken state.
When used properly, auto-darkening welding helmets are safe, if not safer than passive welding helmets. Auto-darkening helmets do not have to be taken on and off, helping welder's focus on their projects and reduce the risk of errors and injuries.