One of the greatest advancements in PPE for welding has been the invention of the auto-darkening filter (ADF). With an ADF lens, welders are not only able to see more clearly while welding, but most importantly and unlike traditional weld visors and to some extent even fixed shade lenses, they remove the need to lift the visor to check work between welds, minimizing the risk of eye injuries from sparks or debris, and reducing the risk of indirect exposure to harmful UV/IR radiation from nearby welders.
A lot of effort goes into developing new technologies, and although they may immeasurably improve the way in which we complete a task, we don’t always question how they work. In this article we break down each of the important elements that make up an ADF lens and examine how they function.
There are three key components of an ADF lens, these being an Ultraviolet/Infrared (UV/IR) interference filter, polarization filters, and Liquid Crystal Cells (LCC). These are layered on top of each other and work together to protect the eyes.
This layer is designed to protect the welder from Ultraviolet and Infrared rays generated during the welding process. The risk of UV exposure during welding is similar to that of sun exposure, and can result in short term damage such as reddening of the eyes, sensitivity to light, and even “sunburn”. Long term exposure can lead to serious health concerns such as cataracts, ocular melanoma, and skin cancer. The UV/IR interference filter is constructed from a thin glass layer which has several metallic layers – including five layers of silver and 6 of aluminum oxide. These layers work together to reflect and absorb 99.9% of IR radiation, and absorb 99.9997% of harmful UV radiation. The metallic layers are also used to protect the liquid crystal panel against heat damage.
An ADF lens comprises of 3 layers of polarization filters. These are positioned between each of the other layers that make up the lens (refer to image). With all three combined, the polarization filters protect welders’ eyes from the bright light in the arc. The filter that is positioned after the UV/IR layer is placed at a 90-degree rotation compared to the other polarizing filters; this filters the darkest point.
The liquid crystal cells are positioned between the polarizing filter layers. These have the ability to bend light once stimulated by electricity, and can be controlled to adjust the shade state of the lens.
When the welding lens is switched off and not in use, the LCC bends the light 90 degrees, making the lens dark, similar to a shade 5 or 6. Once the lens is turned on and exposed to daylight, the polarized filters untwist, which causes the lens to drop to a shade 3, allowing the welder to comfortably see through the lens. Once the welding arc is struck it takes only 0.0001 of a second for the photosensors to trigger, and for the lens to adjust to the shade level that has been preselected, protecting the welder from the intense light created from the weld arc.
ADF lenses are assigned a lens rating, which is made up of four numbers, for example, 184.108.40.206. Each number refers to a different class, these being;
Each of these classes is assigned a score between 1-3 - the lower the number, the better the quality of lens.
Optical class refers to the distortion level when looking through the welding lens. A score of 3 would be very difficult to see through - like looking through rippled water, where as a 1 would be near perfect.
Diffusion of Light Class
When welding, any imperfections in a lens can have a huge impact on your view. This rating signifies the quality of lens in terms of manufacturing imperfections and clearness.
Variations in Luminous Transmittance Class
For a welding lens to be effective, there needs to be consistency in shading, meaning that the lens appears the same no matter which area you are looking through. Consistent, even shading would be assigned a 1, whereas a lens that has bright or dark areas, and general areas of inconsistency in shading would be assigned a 3.
Angle Dependence on Luminous Transmittance Class
Welding is not always completed directly in front of the operator, so it’s important when working across different angles, that the shade remains the same. This class rates the ability of the lens to provide consistency across differing angles.
ADF lenses can have a range of settings that can be adjusted in order to better suit the environment and type of welding that is being completed.
Hopefully you now have a clearer understanding of how ADF lenses work. To learn more about welding respirators explore more articles on the discovery center, or to find the right respirator for you, check out our full range of fabrication respirators.
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