How Much Are Lumen Winter Paintings Worth?

I have a Lumen Winter painting about the size of a couch.  It is called "White Stallion in the moonlight.  It has a gold bar on the bottom of the frame with his name and the name of the painting.  He also signed it on the right hand side on the bottom of the painting.  It is in perfect condition and I was wondering what it would go for?

My grandpa gave me a lume winter horse pic ..its with 4 horses white one in front pretty blue background ..I think he in the 50s or earlier