In a moving light clock, the photon travels a different distance $$L'$$ than in a stationary light clock: $$L$$. Moving light clock moves to the right with velocity $$v$$. The photon always has the speed of light $$c$$ and covers the distance $$L'$$ within the time $$\Delta t'$$ and the distance $$L$$ within the time $$\Delta t$$.