Auto Darkening Filter

Auto Darkening Filter (ADF).

The ADF, or automatic darkening filter, consists of liquid crystal displays (LCDs), electronic components, solar cells/batteries, sensors and a UV/IR filter. This is the part of the helmet that automatically darkens when a welding arc is struck. optrel provides a wide range of ADFs with various features and shade protection options. During certification, the quality of an ADF is assessed in line with the European standard. The following four criteria are graded in order to provide the welder with an indication of quality: optical class, scattered light, homogeneity and dependence on angle of vision. All ratings must be stated on the darkening filter: 1 is the highest rating and 3 the lowest.

LCD - Liquid Crystal Display

LCDs form part of the ADF. Amongst other things they contain liquid crystals which allow for automatic darkening of the filter. The arrangement of the liquid crystals is controlled by electric pulses. Different arrangements allow the liquid crystals to respond in different ways to the light intensity.

UV/IR Filter

A filter is used to reliably reflect optical radiation in the UV and IR range. The filter is permanently fitted in the ADF and offers permanent protection regardless of whether the darkening filter is in the dark or light state.


The sensors fitted in the ADF detect when an arc is struck. When this happens, the sensors transmit a signal to the electronics which then activate the LCDs.

Solar cells & batteries

The power needed to operate the ADF can be guaranteed over different types of power supply. For all expert- and pro-helmets, the power during welding comes from the solar cells, which generate energy out of the welding arc. However, to start the welding helmet the first time for each welding session, a back up battery is also included. For all optrel helmets, there is no need to switch it on or off.

Front cover lens

The front cover lens is fitted on the helmet in front of the darkening filter. It prevents weld spatter from reaching and damaging the darkening filter. The front cover lens has to be replaced regularly depending on the welding process and dirt levels experienced.

Inside cover lens

An inside cover lens is used to protect the back of the ADF from dust and other dirt. This thin plastic lens is a wearing part and canbe replaced when it becomes dirty and discoloured.