A solar day is a time it takes for the Earth to rotate about its axis so that the Sun appears in the same position in the sky.
A lunar day or moon is the period of time it takes for the Earth's Moon to complete one full rotation on its axis with respect to the Sun. Equivalently, it is the time it takes the Moon to make one complete orbit around the Earth and come back to the same phase.
The second is the SI unit of time.
A light-year is a unit of distance, and it is defined as the distance traveled by light in one year.
So, solar day, moon day, and second represent time while light-year represents the length.