The reaction of high-temperature cuprate superconductors to illumination differs from the reaction produced in conventional superconductors. Two such effects, reviewed here, are persistent photoconductivity and persistent photoinduced superconductivity. For example, REBa(2)Cu(3)O(x) thin films show a decrease in the normal state resistance and an increase of T-c, which persist for a long time at low temperatures (< 100 K). The experimental investigations and results are briefly presented, before two alternative theoretical models are considered.