Lens Flare for Final Cut Pro is a lens flare generator.
In Final Cut Pro you will find in Generators RGB HOUSE group, where will be Lens Flare. Drag this generator above all clips in timeline. When it’s there remember to change blending mode to Screen (in video section). You can adjust color, steak color, glow, intensity, scale - apacity and blur of artifacts, position. Any parameter could be stored as a keyframe, so you can easily animate the flare.