Once upon a time, before the internet pilots needed to be able to calculate the time of beginning and end of daylight for operational purposes. The syllabus and examinations system haven’t quite caught up with technology so you are still required to be able to calculate these times manually.
Night is defined as the period between the end of evening civil twilight and the beginning of morning civil twilight. For all intents and purposes, first light should be construed as the beginning of civil twilight and last light as the end of civil twilight. The terms sunrise and sunset have no relevance when calculating daylight operating times for VFR pilots.
AIP GEN 2.7 provides the graphs and tables necessary to calculating daylight and gives worked examples of how to do it.
Technical data content credited to Mr Steve Griffin