J. Alden Weir's studio was surprisingly dark. He purposely blocked off all the side windows and painted the walls a dark color, so that the large north-facing windows were the only source of light. Here's the reason why: with a north-facing window, the sunlight does not move through the studio at different angles during the day. The north light illuminates the subject matter and the painting in the same cool atmosphere, which allows the artist greater control over color values and contrasts within a painting.
My favorite part of the studio was the ceiling, which was decorated with gold starfish. The starfish were like an old-fashioned version of the fluorescent stars my children had on their bedroom ceiling. Very whimsical!