Definition - What does Shade Number mean?
The shade number of a lens indicates the amount of darkness provided by it and how effective it is at protecting the eye against intense light during arc welding or plasma arc cutting operations. Using the right shading protects the wearer from retinal damage.
The shade number provides a convenient way for welders to select the most comfortable and clear lens for a particular welding or cutting operation.
Safeopedia explains Shade Number
Shade numbers range from 2 to 14, with the higher number indicating a darker lens. Darker lenses will filter out ultraviolet (UV) and infrared (IR) waves that could be harmful to the eyes.
A lens with a shade number of 2 will be adequate for torch soldering, but all other welding operations will require a higher shade number, up to 14 for carbon arc welding.
While OSHA lays out the minimum requirements for shade numbers, ANSI Z49.1 lists recommended shade numbers, which are either equal to or higher than the ones mandated by OSHA.