Get effect to overcome image size [After Effects]
If you are applying the light wipe to an image which is smaller than your full comp size, then the light wipe effect will only fill the size of the image, not the full screen.

To overcome this, you could add a full screen solid behind your image, and pre comp the image and the solid.  Then add the light-wipe to the comp, not the individual images.

Alternatively, you could try putting an adjustment layer between your two images, and applying the light wipe to that.