daytime vs solar day

daytime

noun
  • The time of daylight; the time between sunrise and sunset. 

adj
  • Happening during the day. 

  • Pertaining to daytime; appropriate to the day. 

solar day

noun
  • one day of solar time, the time between successive noons; the time in which a planet such as Earth apparently rotates once around its axis, relative to the sun (on Earth about 24 hours as an average - the length of solar day is not constant throughout the year) 

How often have the words daytime and solar day occurred in a corpus of books? (source: Google Ngram Viewer )