Alens collects light and focuses it into a small spot. this increases the of the light wave. w

The correct answer is intensity. 
In fact, intensity I is a measure of the power P of the wave per unit of area A:

The lens does not change the power of the source which emits the wave, however it reduces the area A, since it is focusing the light into a single point. Since A decreases, I, the intensity, increases.