The first sources of light for all of Arda were two enormous Lamps: Illuin, the silver one to the north and Ormal, the golden one to the south. These were cast down and destroyed by Melkor. Afterward, the Valar went to Valinor, and Yavanna sang into existence the Two Trees, silver Telperion and golden Laurelin shedding light comparable to moon and sun. Telperion was referred to as male and Laurelin female. The Trees sat on the hill Ezellohar located outside Valimar. They grew in the presence of all of the Valar, watered by the tears of Nienna.
Each tree was a source of light: Telperion's silver and Laurelin's gold. Telperion had dark leaves (silver on one side) and his silvery dew was collected as a source of water and of light. Laurelin had pale green leaves trimmed with gold, and her dew was likewise collected by Varda.
One "day" lasted twelve hours. Each Tree, in turn, would give off light for seven hours (waxing to full brightness and then slowly waning again), so that at one hour each of "dawn" and "dusk" soft gold and silver light would be given off together.
Jealous Melkor, later named Morgoth by Fëanor, enlisted the help of the giant spider-creature Ungoliant (the first great spider, ancestor of Shelob, and possibly a fallen Maia) to destroy the Two Trees. Concealed in a cloud of darkness, Melkor struck each Tree and the insatiable Ungoliant devoured whatever life and light remained in them.
Again Yavanna sang and Nienna wept, but they succeeded only in reviving Telperion's last flower (to become the Moon) and Laurelin's last fruit (to become the Sun). These were assigned to lesser spirits, male Tilion and female Arien, after the 'genders' of the Trees themselves. This is why, in The Lord of the Rings, the Sun is usually referred to as "she" and the moon as "he".
However the true light of the Trees, before their poisoning by Ungoliant, was said to now reside only in the three Silmarils, created by Fëanor the most gifted of the Elves.
other LOTR artwork of mine: