More hits for Martin's
Lord of Light than Zelazny's.
Most annoying, that.
Top search result: R'hllor. R'hllor, also known as the Lord of Light, the Heart of Fire, the God of Flame and Shadow, is a prominent god in Essos, but has only a few followers in Westeros, where he is more commonly known as the red god. His symbol is a fiery heart.
It's churlish to be upset with Martin over the use of three very common English words that happen to be suitable for his purposes. It might have even been a nod to Zelazny, of whom he has been a tireless advocate. Still, a little annoying.