Complex sentence: It was followed by the second album "Leave a Light" towards the end of 1978 and the first single "I'll Keep a Light in My Window" was a surprising didn't do as well as expected.
Split into simpler sentences: It was followed by their second album titled "Leave a Light" launched towards the end of 1978. The first single of the album "I'll Keep a Light in My Window" could not do as well as expected.