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Any type of welding requires advanced eye protection to prevent corneal damage from the ultraviolet light of the weld. Welders must wear a protective welding helmet that covers the face to protect from sparks and flying material; this helmet includes a special darkened eye shield to prevent the cornea from being damaged. This condition is called arc eye and can be extremely uncomfortable. The eye protection of the welder's helmet can also prevent retinal damage.
Every welding helmet includes a lens shade, or the eyepiece through which the welder looks at his weld. It is a heavily darkened and polarized lens that only lets in a certain amount of light. The lens is so dark, it is extremely difficult to see anything through it aside from the welding light itself. Therefore, the auto-darkening welding helmet has become popular in recent years.
The auto-darkening welding helmet does exactly what its name implies: its lens automatically darkens when the light from the weld begins to flash. Otherwise, the lens lightens so the welder can see objects in front of him. Without the auto-darkening feature, the lens shade would be almost completely black, making it impossible to see the project in front of him without raising his helmet.
The auto-darkening welding helmet uses a light sensor to indicate when the lens shade should be darkened. This sensor is mounted to the front of the mask and prevents such conditions as arc flash, or the unexpected exposure of the eye to the welding arc. There are two types of auto-darkening welding helmet: solar powered and battery powered. Each one does the same thing and is of comparable quality to the other, but the solar powered mask has a few advantages.
First, because the solar powered auto-darkening welding helmet does not have an on-off switch, there is no risk of accidentally leaving the mask turned off, thereby exposing your eyes to the welding arc. Luckily, all models of auto-darkening welding helmet protect the eyes from damaging UV light even if the lens shade is not at its darkest, but your eye will be exposed to uncomfortably bright light if the shade is not darkened. Further, the solar powered auto-darkening welding helmet does not require battery changes, nor does it necessitate you monitor battery life to ensure the lens shade will darken when you need it to.
Both masks require regular inspection to ensure no cracks in the lens shade will expose your eye to UV light. Be sure to check your helmet for damage regularly. While less expensive masks are available as a replacement for a damaged mask, they are not auto-darkening and can make your project more cumbersome and difficult.