The invention relates to a liquid-crystalline medium based on a mixture of polar compounds having positive dielectric anisotropy, characterised in that it comprises one or more compounds of the formula I in a total concentration of ≥40%, ##STR00001##
in which the parameters have the meanings indicated in claim 1, and to the use of the liquid-crystalline medium for electro-optical purposes, in particular in liquid-crystal light valves for lighting devices for motor vehicles, and to liquid-crystal light valves which comprise this medium and lighting devices for motor vehicles which contain such liquid-crystal light valves.

A means is a compound represented by formula (1) , a liquid crystal composition containing the compound, and a liquid crystal display device including the composition.

##STR00001##

In formula (1), R.sup.1 and R.sup.2 are independently alkyl having 1 to 15 carbons or the like; ring A.sup.1, ring A.sup.2 and ring A.sup.3 are independently 1,4-cyclohexylene, 1,4-phenylene or the like; and Z.sup.1, Z.sup.2 and Z.sup.3 are independently a single bond or the like.

The invention relates to a liquid-crystalline medium based on a mixture of polar compounds having positive dielectric anisotropy, characterised in that it comprises one or more compounds of the formula I in a total concentration of 40%,

##STR00001##

in which the parameters have the meanings indicated in claim 1, and to the use of the liquid-crystalline medium for electro-optical purposes, in particular in liquid-crystal light valves for lighting devices for motor vehicles, and to liquid-crystal light valves which comprise this medium and lighting devices for motor vehicles which contain such liquid-crystal light valves.