An optical film has a transparent film, an adhesive layer provided on one surface
of the transparent film, the adhesive layer having a refractive index different
by 0.1 or less from that of a layer of the one surface of the transparent film,
and a repetitive prismatic structure provided on the other surface of the transparent
film, the repetitive prismatic structure having optical path changing slopes aligned
in a substantially constant direction at an inclination angle in a range of from
35 to 48 degrees with respect to a plane of the transparent film. Another optical
film has a transparent film having an average in-plane retardation of not larger
than 30 nm, an adhesive layer provided on one surface of the transparent film,
the adhesive layer having a refractive index different by 0.12 or less from that
of a layer of the one surface of the transparent film, and the repetitive prismatic
structure provided on the other surface of the transparent film. Still another
optical film has a transparent film having a refractive index of not lower than
1.49, a transparent adhesive layer provided on one surface of the transparent film,
the transparent adhesive means having a refractive index of not lower than 1.49,
and the repetitive prismatic structure provided on the other surface of the transparent film.
