Patent ID: 11921373
Assignee: 3M INNOVATIVE PROPERTIES COMPANY
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 11:
12. A backlight for providing illumination to a liquid crystal panel, comprising:
an extended light source adapted to emit light through an emission surface thereof;
a reflective polarizer disposed on the extended light source, such that for substantially normally incident light and for at least a first wavelength in a range from about 420 nm to about 650 nm, the reflective polarizer reflects at least 60% of the incident light having a first polarization state and transmits at least 60% of the incident light having an orthogonal second polarization state;
a first prismatic film disposed between the extended light source and the reflective polarizer and comprising a structured major surface comprising a plurality of substantially parallel first linear prisms extending along a first direction and arranged in an orthogonal second direction; and
an achromatic retarder layer disposed between the reflective polarizer and the first prismatic film, such that for substantially normally incident light, the retarder layer has a minimum blue retardance at a corresponding blue wavelength, a minimum green retardance at a corresponding green wavelength, and a minimum red retardance at a corresponding red wavelength, wherein the minimum blue, green and red retardances are within 20% of each other wherein light emitted by the backlight at zero and sixty degrees with respect to a line normal to the emission surface has respective color coordinates (x1, y1) and (x2, y2) in CIE 1931 chromaticity coordinate system in a white region, wherein x1 and x2 are different by less than about 0.0051, and y1 and y2 are different by less than about 0.01.