A composition contains (a) a silicon-free mercapto compound comprising 2 or more mercapto groups; (b) a linear polyorganosiloxane containing one or more than one terminally unsaturated alkenyl group, 40 mole-percent or more phenyl groups relative to moles of silicon atoms and at least one alkoxysilyl group per molecule; (c) a resinous polyorganosiloxane containing one or more than one terminally unsaturated alkenyl group and 20 mole-percent or more phenyl groups relative to moles of silicon atoms; (d) a photoinitiator; and (e) a moisture cure catalyst; and wherein the molar ratio of mercapto groups to terminally unsaturated alkenyl groups in the composition is in a range of 0.3 to 2.0.