Smallest / Largest: how small and how big each light gets while it breathes (100% = its normal size; set both the same to stop the size change). Breath Speed: how many full breaths fit in the 20 s loop. Grow vs Shrink Timing: how much of each breath is spent growing compared with shrinking.
Use a duration that is a multiple of 20 s for a perfect loop. Keep this tab visible while rendering.