Psyshock is affected by Light Screen. If a screen is set up before
opponent's move, the damage will be reduced. Critical hits ignore
Reflect's/Light Screen's effect. Note that in Doubles, a screen raises
(special) defense by 33% not 50%.
Although people might think reflect is the one that affects light screen, psychock is still a special move and is affected by light screen
Light Screen doesn't raise special defense; it halves damage taken from special attacks, and Psyshock is a special attack. It just happens that it calculates damage based on your own special attack stat against the opponent's physical defense.
Hooe I helped :D