Patent ID: 7530721

Claim:
A backlight device for display comprising (1) a side-lit light source, (2) a light guide plate, and (3) a turning film comprising melt-extrudable and thermo-formable polymeric material, the turning film comprising prismatic structures on the light entry surface of the film and lenticular elements on the light exit surface of the film, wherein: (a) the prismatic structures are characterized by an average apex angle (α+β) and an average pitch (Q); (b) the lenticular elements are characterized by an average pitch (P) and an average radius of curvature (R); and (c) the prismatic structures and lenticular elements are out of registration by an average amount (X), and (d) the film has average thickness (T); provided that said averages are selected to provide a peak output angle of ±10° from normal to the light exit surface of the light guide plate and an optical gain of at least 1.25; and wherein the turning film value derived from the formula T P - cos 2 ⁡ ( α + β 2 ) sin ⁡ ( α + β ) - ( R P - ( R P ) 2 - 1 4 ) is in the range from 0 to about 5.5.