Nowadays I assume a "palma de luz" is a lamp post, as I have seen images in newspapers showing cars that have crashed into them, with the headline "choca a una palma de luz" or similar.
But I have encountered this phrase in a Ruben Dario poem (Reencarnaciones) and I doubt that this was what he meant. It was written around 1890 or so and dealt, obviously, with reincarnation.
Yo fui coral primero,
Después hermosa piedra,
Después fui de los bosques verde y colgante hiedra;
Después yo fui manzana,
Lirio de la campiña,
Labio de niña,
Una alondra cantando en la mañana;
Y ahora soy un alma
Que canta como canta una palma
De luz de Dios al viento.
Also, he speaks of "labio de niña" which I have interpreted as a type of flower which appears very much like human lips (called "Hooker's Lips" in places).