When the Dows first moved into The Pines in November of 1899, the staircase was much darker. The only window was the smaller one at the first landing, but they also planned to add some kind of decorative window on the large wall space where the leaded-glass windows are today.
That addition came in 1904. Herbert Dow attended the World's Fair in St. Louis, Missouri where he found a glass artist he commissioned for the windows. In the letter he wrote home to Grace, he stated that he had ordered the windows for the staircase wall and they were to be clear. If she wished to add color to the glass, staining it, they could discuss the matter. As you can see, though, the glass remained clear.