There are five lumbar discs, one each between the 1st & 2nd, the 2nd & 3rd, 3rd & 4th, 4th & 5th and at the bottom between the 5th lumbar and the 1st sacral vertebrae.  

90% of disc protrusions are at the lower two levels, L4/5 and L5/S1. Most are off to one side, either to the right or left. Because of anatomical variations, such as an absent 12th rib or an extra disc between S1 & S2, the numerical designations can be wrong, but that only matters if surgery is planned.