Patent ID: 7618178

Claim:
A backlight unit comprising in order: (1) a light source; (2) a light guide plate (LGP) having an incident face toward the light source and having a refractive index n LGP ; (3) a reflective polarizer having formed birefringence in optical contact with the LGP including a layer having: (a) an elongated non-conductive first material with refractive index n 1 ; (b) an elongated non-conductive second material with a refractive index n 2 different by at least 0.2 from that of to first material; in which the first material and the second materials are aligned in a direction generally perpendicular to the incident face of the LGP; wherein: (i) the cross-sectional dimensions of the first and second materials, in a plane parallel to the light incident face of the LGP, are smaller tan 100 nm in their width dimensions; and (ii) the parameters of the reflective polarizer are selected to provide R 0 >0.8 for one polarization state and T 90 >0.8 for the orthogonal polarization state, for light of wavelength of 550 nm, for least one reflective polarizer angle of light incidence θ a , wherein the parameters selected include pitch, thickness, cross-sectional width, n 1 , n 2 , n LGP , location of reflective polarizer, and fill factor.