On page 188 of my סדור רינת ישראל (or p. 196 in this edition) the instructions for lighting shabbat candles begins as follows: כשהחמה בראש האילנות, מדליקים נר של שבת.
My limited Hebrew has me understand this as "when the sun is at the tops of the trees, light the shabbat candles."
The time for lighting has been expressed in terms of shkiah or evening or something specific to the clock (the notes at the bottom of page 296 of the Artscroll siddur Kol Yaakov speak of "approximately 18 minutes before sunset"). This instruction speaks of the position of the sun relative to trees -- which trees? How tall are they? At what angle am I standing? And maybe it is just me and my understanding of trees, but when the sun is at the rosh of the trees is significantly earlier in the day than candle lighting is usually set for. Is this statement encouraging an earlier shabbat or am I misunderstanding the printed instructions?
Help is, as always, appreciated.