What is a necessary feature of all welding helmets?

A necessary feature of all welding helmets is that they contain a lens that filters out dangerous light rays while welding. This is crucial for protecting the welder’s eyes from the intense brightness and harmful ultraviolet (UV) and infrared (IR) radiation produced during the welding process. The welding arc emits light that can cause serious eye damage, commonly referred to as "arc eye," resulting from exposure to these harmful rays.

The lens must meet specific standards to ensure it effectively protects the welder's eyes, allowing them to work safely without the risk of injury from harmful radiation. While features like a flip-up lens or an auto-darkening lens may enhance usability or comfort, the fundamental requirement for any welding helmet is its ability to filter light and protect the welder from damage caused by the welding process. Thus, the focus on filtering dangerous light rays underscores the helmet's primary role in safety.