How Auto Darkening Lenses Work

Infrared Radiation Sensors

Auto darkening lenses are triggered by the infrared radiation emitted by the welding process.

The front of the helmet’s lenses has small red sections. These are the sensors that detect infrared radiation and enable the helmet to switch to the dark state. 

Older or cheaper helmets only have two sensors, whereas professional-grade helmets will have 4 sensors.

Electromagnetic Field Detection

The latest lenses use X-Mode. This uses the electro-magnetic field generated by the welding process to switch the lens to dark mode. 

What Is Inside The Auto Darkening Welding Helmet?

Auto darkening lenses are made up of different layers of Hi-Tech materials. See the illustration below.

How Auto Darkening Helmets Work

Ultraviolet and Infrared Light Filter

This is the layer that gives the welding lens it’s pink-purple look. It filters out 99.9% of the infrared radiation and up to 99.997% of the ultraviolet light.

The glass is a good UV-B filter (ultraviolet light that causes sunburn). The outside reflective surface is made up of 11 different layers of metallic film. Five layers of silver and Six layers of aluminum oxide. The added layers filter out the remaining UV-A and UV-C.  

The latest generation of filters can have up to 20 layers with a total thickness of 7 microns. This layer filters out harmful light all of the time. So if the lease doesn’t auto-darken when a flash occurs from the welder, the harmful light has been stopped. 

Polarization Filter

The polarization filter is another thin piece of glass or plastic, with a film of stretched iodine applied to it. The iodine has been stretched so all of the molecules are in a straight line. This only allows the light to pass through in a vertical wave.

welding helmet polarising filter function

This part of the lens requires 3 polarization layers to filter out the light to a level that the liquid crystal lens can use, enabling the welder to see clearly. 

The polarizing filters are placed in 90 degree orientation to one another, to filter out a lot of the light.

Liquid Crystal Cell Filter

The liquid filter lenses are usually made of 2 thin pieces of glass with a thin transparent film of conductive coating. Indium tin oxide is the common surface treatment. 

A spacer is used to strictly control the gap between the 2 layers. Inside are the liquid cells. 

The liquid crystal cells need the light to be in a single wave form to be effective.

How Do The Auto Darkening Welding Helmets Change Shade?

Once the sensors have detected the arc, the sensor sends an electrical voltage to the liquid crystal cells which are usually lying flat. When the cells are activated with the electrical voltage, they turn 90 degrees and the amount of voltage they receive determines how far the crystals will turn, limiting the amount of light passing through.

Recent Improvement In Auto Darkening Lens Technology

Auto darkening helmets have been around for decades. The first generation of the auto-darkening welding helmets had a fixed rate of shade. They were a dark shade 5 to 6 in their lightest state, then switched to a most common shade of 11 for the dark state.

The next generation of helmet technology allowed the shade range of the dark state to be variable from a shade 9 to a 13 and was a big leap forward in the development of helmets and then the sensitivity of the helmet adjustment became available. This feature let welders using TIG at low amperage use auto-darkening hoods. 

Welders looking through the lenses of these helmets, had a dark light state and their visual environment had a green tint to it limiting the usefulness of the helmet when not welding as lens was simply too dark\. 

Auto darkening welding helmet lense

Why Do Most Welding Helmets Have A Green Tint

The reason the welding lens has a green tint, is because of the 2 metallic coatings applied to the ultraviolet and infrared radiation filter. 

The makers of auto-darkening welding helmets have the hard job of trying to filter out the infrared spectrum, which is very close to the red color wave and ultraviolet is very close to the violet and blue shade of light wavelength. 

The main colors that could pass through the filters were green and yellow, resulting in the green tint when looking through the welding helmet lens. 

The liquid crystal lenses do not filter any of the harmful ultraviolet and infrared radiation, and they would quickly be damaged by them. The LC cells only reduce the massive amount of light generated by the welding arc.

welding lense ultraviolet filter

Are Auto Darkening Helmets Safe?

Yes harmful ultraviolet light and infrared light, are filtered out  100% of the time. The special coating applied to the purplish lens is always active. You will still see the bright light behind the welding helmet but won’t harm your sight.

Reaction Time Auto Darkening Welding Helmet Speed

The speed at which auto-darkening welding helmets switch from light state to dark is measured in 1000’s of a second, or milliseconds. More affordable lenses switch in 1 / 30,000 of a second and the average for a good helmet is 1 / 25,000 of a second, the fastest being 1 / 20,000 of a second. 

Do Auto Darkening Helmets Have Batteries

Yes, all auto-darkening welding helmets have batteries and some of the auto-darkening helmets are fitted with solar cells. The battery is required for the first initial switching of the helmet and once the arc from the welder is going, the solar cell powers the liquid crystal cell and charges the internal lithium battery.

The cheaper welding hoods that appear to have no battery actually do, but don’t give you the ability to change them. This is why these cheaper helmets don’t last as long and require to be solar charged if not in use for long periods.

What Batteries Do Auto Darkening Welding Helmets Use?

The most common type of replaceable battery is the CR2450 or the CR2032. The auto-darkening welding helmets with the larger viewing area sometimes require 2 batteries to power the helmet.

How Long Do Auto Darkening Helmets Last

Budget-priced auto-darkening hoods can last for up to three years as these helmets don’t allow the batteries to be replaced.

 When these helmets are coming to the end or their service life, you may find you have to leave the helmet in the sun to charge for long periods for it to work.

Premium auto darkening welding hoods can last from 5 to 7 years depending on how you look after them and the welding processes you use. 

The top of the range helmets cost more in the beginning but out last the cheaper version while giving better optical quality and faster switching times.