A curable composition satisfying Equation 1 and which comprises: a polyorganosiloxane having an average compositional formula of Formula 1; a polyorganosiloxane having an average compositional formula of Formula 2; and a compound of Formula 3, and wherein one or two of the polyorganosiloxane, the polyorganosiloxane, and the compound does not comprise an aryl group, and the other component comprises an aryl group: [Formula 1] (R 1 3 SiO 1/2) a (R 1 2 SiO 2/2) b (R 1 SiO 3/2) c (SiO 4/2) d [Formula 2] (R 2 3 SiO 1/2) e (R 2 2 SiO 2/2) f (R 2 SiO 3/2) g (SiO 4/2) h [Formula 3] H i Y j SiO (4-i-j)/2 A − B > 0.03 where R 1, R 2, and Y are each independently an epoxy group or a monovalent hydrocarbon group, with the proviso that at least one of R 1 or at least one of R 2 is an alkenyl group; a is 0 or a positive number, b is a positive number, c is 0 or a positive number, d is 0 or a positive number, b/(b+c+d) is 0.65 or more, e is 0 or a positive number, f is 0 or a positive number, g is 0 or a positive number, and h is 0 or a positive number, f/(f+g+h) is less than 0.65, with the proviso that g and h are not simultaneously 0; i is 0.2 to 1, j is 0.9 to 2, and A is a refractive index of any one component of the components to, and B is a refractive index of a mixture of the other two components of the components to, wherein the ratio (H/Ak) of moles of a hydrogen atom binding to a silicon atom included in the silicon compound with respect to moles (Ak) of all alkenyl groups included in the polyorganosiloxanes and is 0.5 to 2.0; and wherein the one component having the refractive index A in Equation 1 is included in the curable composition in an amount 0.1 parts by weight to 30 parts by weight with respect to 100 parts by weight of the other two components having the refractive index B, where refractive index is determined in accordance with the method outlined in the description. a polyorganosiloxane having an average compositional formula of Formula 1; a polyorganosiloxane having an average compositional formula of Formula 2; and a compound of Formula 3, and wherein one or two of the polyorganosiloxane, the polyorganosiloxane, and the compound does not comprise an aryl group, and the other component comprises an aryl group: [Formula 1] (R 1 3 SiO 1/2) a (R 1 2 SiO 2/2) b (R 1 SiO 3/2) c (SiO 4/2) d [Formula 2] (R 2 3 SiO 1/2) e (R 2 2 SiO 2/2) f (R 2 SiO 3/2) g (SiO 4/2) h [Formula 3] H i Y j SiO (4-i-j)/2 A − B > 0.03 where R 1, R 2, and Y are each independently an epoxy group or a monovalent hydrocarbon group, with the proviso that at least one of R 1 or at least one of R 2 is an alkenyl group; a is 0 or a positive number, b is a positive number, c is 0 or a positive number, d is 0 or a positive number, b/(b+c+d) is 0.65 or more, e is 0 or a positive number, f is 0 or a positive number, g is 0 or a positive number, and h is 0 or a positive number, f/(f+g+h) is less than 0.65, with the proviso that g and h are not simultaneously 0; i is 0.2 to 1, j is 0.9 to 2, and A is a refractive index of any one component of the components to, and B is a refractive index of a mixture of the other two components of the components to, wherein the ratio (H/Ak) of moles of a hydrogen atom binding to a silicon atom included in the silicon compound with respect to moles (Ak) of all alkenyl groups included in the polyorganosiloxanes and is 0.5 to 2.0; and wherein the one component having the refractive index A in Equation 1 is included in the curable composition in an amount 0.1 parts by weight to 30 parts by weight with respect to 100 parts by weight of the other two components having the refractive index B, where refractive index is determined in accordance with the method outlined in the description.