A pressure-sensitive adhesive based on at least 50% of one or more block copolymers, at least one block copolymer being composed at least in part on the basis of (meth)acrylic acid derivatives, the at least one block copolymer comprising at least the unit P(A)-P(B)-P(A), comprising at least one polymer block P(B) and at least two polymer blocks P(A), where P(A) independently of one another represent homopolymer or copolymer blocks made up of monomers of group A, the (co)polymer blocks P(A) each having a softening temperature in the range from 0° C. to +175° C., P(B) represents a homopolymer or copolymer block comprising monomers of group B, the (co)polymer block P(B) having a softening temperature in the range from −130° C. to +10° C., and the (co)polymer blocks P(A) and P(B) are not homogeneously miscible with one another at 25° C., characterized in that the adhesive has a refractive index nd,a of nd,a≧1.52 at 25° C., at least one of the (co)polymer blocks P(A) have a refractive index nd,A of nd,A≧1.58 at 25° C., and the (co)polymer block P(B) has a refractive index nd,B of nd,B≧1.43 at 25° C.