Tony Kuypur has a terrific site called Goodlight,us His tutorial page has links to some excellent tutorials using advanced masking and blending mode techniques including using Luminosity Masks. If you are interested in advanced masking techiques for landscape photography this is the site for you.
He has an excellent and very helpful blog post called "Simplifying Luminosity Masks" at the blog on his site.
From article on Luminosity Mask-
"The marching ants appear on the image to define the selection (Figure 2). Since Photoshop only puts marching ants around pixels that are at least 50% selected, and since this selection is based on the brightness of the image, the marching ants only appear around pixels that are equivalent to 50% gray or brighter. I'll discuss this in more detail later. For now it should be obvious that the marching ants are enclosing the lighter areas of the image."
Jimmy McIntyre has an excellent site about blending images together called Shutter Evolve.
This is a good article by Jimmy McIntyre called "Benefits of Using Luminosity Masks in Exposure Blending"
"An Introduction to Luminance/Luminosity Masks in Digital Blending", is also by Jimmy McIntyre.
Here's another Jimmy McIntyre article at 500px called "The Basics of Luminosity Masks in Digital Blending."
Here's another article by Jimmy McIntyre on "How to use luminosity masks in Photoshop to transform your images" at Lightstalking.com. Click on the images below to download the image to work with by Jimmy McIntyre. It goes with the above article.
An excellent Jimmy McIntyre article on Luminosity Masking called "The Art of Digital Blending" shows how to create the luminosity masks.
How Luminosity Masks work is an introduction to luminosity masks by Jimmy McIntyre (The Art of Digital Blending course is available here.)