One of the first things you think about when welding is a welding helmet. You certainly can’t weld without one.
With the affordability of the auto darkening helmets, they have become increasingly popular. But how do auto darkening welding helmets work?
How Do Auto Darkening Welding Helmets Switch To Dark?
Infrared Radiation Sensors
Most of the auto darkening lens is triggered by the infrared radiation emitted by the welding process.
The front of the helmet’s lens has little red squares. They are the sensors that detect the infrared radiation and switch the helmet to the dark state.
The older or more cost effective helmets only have 2 sensors, where the premium / professional grade welding helmets opt for 4.
This is why if you hold your TV remote in front of the lens and press a button, it will switch it to weld mode / the dark state.
Electromagnetic Field Detection
What Is Inside The Auto Darkening Welding Helmet?
The auto darkening lens is made up of several layers. See the below illustration.
Ultraviolet and Infrared Light Filter
This is the layer that gives the lens the pinky purple look. This layer 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 reflective surface is actually made up of 11 different layers of metallic film.
5 layers of silver and 6 layers of aluminum oxide. The added layers filter out the remaining UV-A and UV-C.
The latest generation of filters now have up to 20 layers, totaling a thickness of 7 microns. Head exploding emoji.
This layer filters the harmful light all of the time. So if you get a flash from the welder and it doesn’t switch, the harmful light has been stopped.
The only effect you will have is the bright light causing you to see stars for a moment.
The polarization filter is another thin piece of glass or plastic, with a thin chemical film applied to it.
A common compound is iodine that has been stretched so all of the molecules are in a straight line.
This only allows the light to pass though in a vertical wave.
The lens requires up to 3 polarization layers to filter the light to a level that the liquid crystal lens can use and the welder can see.
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.
The liquid crystal cells are usually lying flat. But when the cells are activated by the electrical voltage, they can turn 90 degrees.
The amount of voltage they receive will determine how far the crystals turn, limiting the amount of light to pass through.
Recent Improvement In Auto Darkening Lens Technology
Auto darkening helmets have been around for decades now. The first generation of the auto darkening welding helmets were fixed 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.
This was a big leap forward in the usability of the helmets.
Soon after the sensitivity of the helmet adjustment was available. This let welders using TIG at low amperage use auto darkening hoods.
Soon after, the ability to adjust the delay of the dark to light state was an added feature.
But all of the welders looking through the lenses of these helmets, had a dark light state and the world had a tint of green to it, limiting the usefulness of the helmet when not welding.
The lens was simply too dark to see much.
If you tried to grind with the helmet on, it would switch to weld mode because the IR sensors would detect heat from the grinding sparks.
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.
Check the illustration below to better understand how the light is filtered.
For the makers of auto darkening welding helmets, they have the hard job of trying to filter out the infrared spectrum which is very close to the red color wave.
The 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.
In fact they would quickly be damaged by them. The LC cells only reduce the massive amount of light generated by the welding arc.
Are Auto Darkening Helmets Safe
Yes. The Harmful ultraviolet light and the not as often thought about infrared light, is 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 it is not harmful.
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 millisecond.
The more affordable lenses switch in 1 / 30,000 of a second. The average for a good helmet is 1 / 25,000 of a second, the fastest being the MIller at 1 / 20,000 of a second.
Do Auto Darkening Helmets Have Batteries
Yes, all auto darkening welding helmets have batteries. Most of the auto darkening helmets also have a solar cell.
The battery is required for the first initial switching of the helmet. Once the arc from the welder is going, the solar cell then powers the liquid crystal cell and chargers 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 for the 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
The more affordable auto darkening hoods last for around three years. These helmets often 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.
They also have better head gear for added comfort and adjust-ability.
That's How Do Auto Darkening Darkening Welding Helmets Work
If you have read all of that and now you are looking for a new auto darkening welding helmet check out my reviews here. I own all the helmets I test to give you genuine reviews. I am a professional welder for the last 19 years.