Cholesteric liquid crystal layer, optical element, lighting device, and liquid crystal display

摘要

A cholesteric liquid crystal layer which is inhibited from appearing to be colored when viewed from slant directions and thus has excellent viewing angle characteristics, while enabling an improvement in the brightness of liquid crystal displays, etc.; and an optical element and an lighting device with each of which liquid crystal displays and the like excellent in brightness and perceptibility can be fabricated. The cholesteric liquid crystal layer (1) has a helical pitch changing in the thickness direction and shows circular dichroism over a wavelength region having a width of at least 50 nm and including a wavelength of 520 nm, wherein the linearly polarized light obtained through a quarter-wavelength plate has a maximum degree of polarization at a wavelength not longer than 520 nm, or the degree of polarization thereof in a wavelength region on the shorter-wavelength side of 520 nm is higher than that in a wavelength region on the longer-wavelength side of 520 nm. The optical element comprises a multilayer structure composed of the cholesteric liquid crystal layer and at least one optical layer superposed thereon which is a retardation compensating plate, a polarizing plate, a light conductive plate, or a quarter-wavelength plate having an Nz of -0.8 to -2.0 and disposed on the longer-helical pitch side of the liquid crystal layer. The lighting device or liquid crystal display comprises the cholesteric liquid crystal layer or optical element disposed on one side of a surface light source or liquid crystal cell.