I am having a professional install of 3/4 Santos Mahogany, about 1500 sqft. The living room is 18' x 35' and has a huge 5' x 10' south facing window. We get lots of sun in the window in the winter, when the sun is low angle, less in the summer. There is a definite 5 foot band of floor in front of the the window that gets the sun, and a line right below the window and then beyond the roof shadow where sun never hits.

I know I am going to get a fairly intense shadow line. Installer says I am going to get a shadow line, but it may not be "too bad". Old oak floor had marked darkening before the window.

Any suggestions as to the best finish to help avoid this. Installer is suggesting oil base to bring out the grain in the wood. I am thinking to do oil with two top coats of water base for increase durability. But the finish I will use is the one that handles the sun best.

Thanks to the expert that knows how to direct me on this one.

I think the best solution is to do what we did. Install UV film on the windows. It blocks like 99% of the uv rays , relflective light and damaging part of the sun. Museums use it to prevent degredation in the color of the wood furniture. We used it for the dark floors and for the high end period reproduction furniture that i built for the house. It works great, our brazilian cherry floor has not darkened at all in months. Film doest make the room any darker and the plants love it.

IMO oil is the nicest looking finish on the mahogany. Forget the water based. Several coats of a high quality oil work and wears great.