How does an auto darkening welding helmet work?

Answer 1

Auto-darkening filters utilize a shutter type of LCD to decrease light penetration when energized. All electronic welding filters exhibit a characteristic known as "angle dependency". This characteristic may make the lens appear to be darker in the center and lighter toward the outer edges or when the lens is viewed at an angle not perpendicular to the filter's surface or not perpendicular to the arc.

Angle Dependency

If you look at a passive filter at an angle, it becomes darker as you are looking through a thicker cross section. An auto-darkening filter is a completely different animal. It appears to be lighter if you look through it at an angle. The technical term that describes this observation is angle dependency. We like to describe this observation as the venetian blind effect. When you close a venetian blind it reduces the light coming through the window, but if you look through the blinds at an angle parallel to the blinds it appears lighter. This same thing occurs in an auto-darkening filter, as they are similar in function. The liquid crystal in the LCD has elongated molecules that lay parallel to each other (see Figure 1). As they rotate to a closed position, when energized, the amount of light that passes through the filter is reduced (see figure 2). When you look through the filter at 90 degrees to the filter surface, you will experience the darkest shade. If viewed at an angle less than 90 degrees the shading appears lighter. You are experiencing the venetian blind effect otherwise known as angle dependency.

ALWAYS use Radnor® Cobra™ .040 Polycarbonate Protective Lenses in Radnor® Cobra™ helmets. These lenses are thinner than the normal protective lens and are designed to conform to the curvature of the helmet and keep out sparks and spatter. As shown in the diagram, sandwich the auto-darkening lens between two protective lenses and place behind a third, outside protective lens for maximum protection of your investment.

Radnor® auto-darkening filters protect the user against harmful ultra-violet and infrared UV/IR rays, both in the dark and light state. No matter what shade the filter is set to, the UV/IR protection is always there. You can never burn your eyes due to optical radiation passing through the filter. The user's eyes can be severely burned if they weld with a damaged lens (cracked, pitted, etc.) or optical radiation can possibly enter in from behind as a result of other welders in the immediate area.