Final answer:
The amount of darkness provided by a welding helmet lens is denoted by the 'shade number', which is a standardized rating indicating the darkness level of the lens to protect welders' eyes.
Step-by-step explanation:
The amount of darkness provided by a welding helmet lens is denoted by the shade number. This number corresponds to the level of protection offered by the lens against intense light from welding processes. The shade number is a standardized rating that indicates the darkness level of the lens; higher numbers correspond to darker lenses. It's important for the welding lens to have the appropriate shade number to protect the welder's eyes from the bright and potentially harmful light produced during welding.