Abstract: The invention relates to improvement in a light filter with automatic regulation of the optical transmission. The filter comprises a filter element (1) with a liquid crystal layer located between two transparent plates (2) and assigned polarizers. The optical transmission of the light filter is varied by applying a variable electric voltage. A first optical sensor (4) is arranged behind the filter element (1) in the radiation emitting direction, and a second optical sensor (8) is arranged beside or in front of the filter element (1) in the radiation emitting direction. The two sensors are connected to a regulating circuit (6), which comprises a subtraction circuit (15) which subtracts the signal generated by the second optical sensor (8) from the signal of the first optical sensor (4), or the signal of the first optical sensor (4) from the signal of the second optical sensor (8), so that the output signal of the regulating circuit is at least approximately proportional to the amount of visible light.

Abstract: An electro-optic welding lens assembly for use in a welder's helmet or a protective eyeshield and including at least one liquid crystal filter element adapted to be controlled with regard to its light transmission as well as control means for changing the rate of light transmision of the liquid crystal filter element. The control means comprises a first manually adjustable control circuit operating independently of the amount of light falling on the lens assembly and including means for adjusting the rate of light passing through the liquid crystal filter element. Further, there is provided a second automatically operated control circuit operating in relation to the amount of light falling on the lens assembly. The second control circuit operates only within a range of light intensity above a predetermined threshold value to limit the rate of transmission of light passing through the liquid crystal filter element.