Guest-host reflective liquid crystal display device with a particular relationship between the concentration of dichroic dye and the cell thickness

A reflective liquid crystal display device comprising:

• a pair of substrates;
• and
• a liquid crystal layer interposed between the pair of substrates, where the liquid crystal layer is formed of a liquid crystal material having a positive dielectric constant anisotropy, long axis of molecules of the liquid crystal material near the substrate is substantially parallel to the substrate, and the liquid crystal material contains a dichroic dye mixed therein, wherein
• a product K.sub.M cd of a value K.sub.M, a dye concentration c % and a thickness of the liquid crystal layer d .mu.m is set so as to satisfy
• 3.0S.sup.2 -7.3S+5.7.ltoreq.K.sub.M cd.ltoreq.14.7S.sup.2 -15.1S+6.15
• where the value K.sub.M is expressed as
• K.sub.M =3k.sub.1 /(1+2S)
• or
• K.sub.M =3k.sub.2 /(1-S),
• where
• k.sub.1 denotes an absorption coefficient for linearly-polarized light substantially parallel to the liquid crystal molecules;
• and k.sub.2 denotes an absorption coefficient for linearly-polarized light substantially perpendicular to the liquid crystal molecules;
• and S denotes an order parameter of the liquid crystal material containing the dichroic dye mixed therein, and where
• an effective value of a voltage applied across the liquid crystal layer is in a range of about 0 to 5 V.