The Two Lamps, also known as The Lamps of the Valar, refer to Illuin (Sky-blue), the lamp which formerly stood at the northern end of Arda and Ormal (High-gold) which stood at the southern end of Arda.
The lamps were created when the Valar concentrated the misty light which veiled the barren ground of Arda.
Aulë forged great towers for the lamps: Helcar, which bore Illuin and Ringol, which bore Ormal. At the centre of Arda, the light of the lamps mingled at the Great Lake. Here the Valar dwelt, upon the island of Almaren.
The lamps were destroyed by Melkor, causing the Valar to flee Middle-earth for Valinor. Where Illuin fell, the Sea of Helcar was formed, of which Cuiviénen was a bay. In Tolkien's earlier writings, there was also the Sea of Ringol to the south which may have been associated with Ormal.
Other Versions of the LegendariumEdit
In Tolkien's older writings (not used in the published version of The Silmarillion), the Valar sought peace with Melkor, asking his assistance with fixing the lamps upon Arda. Melkor, still envious and hateful of the rest of the Valar, agreed to give them a strong, sturdy substance. He gave Aulë ice. Melkor permitted the Valar to do as they wished until the fateful day when the Lamps' light and heat finally melted the ice. The pillars crashed upon Arda, flooding it with water and darkness.