If the Pokémon holding this item uses Light Screen, Reflect, or Aurora Veil, the effects of those moves last eight turns instead of five turns.
If one of these moves is stolen by Snatch, the duration depends on whether the Pokémon that ultimately uses the move holds the Light Clay (regardless of whether the original user held it).
In the Generation VII games, if these effects have their duration extended by the Light Clay, the turn counter on the user interface for these effects will indicate that it lasts for eight turns for the player whose Pokémon used the move, while it will display that it lasts for five turns for their opponent. After five turns of that effect have passed, the user interface will display that it lasts for eight turns for both players.