You've probably had the experience of walking into a room -- maybe even one in your own home! -- and instantly feeling relaxed and cozy. In other rooms, you've noticed feeling restless and on edge. Annoyed. Bored. Overwhelmed.

Sometimes it's hard to put a finger on exactly what causes a particular reaction to an indoor space. Is it the paint color? The style of furniture? That beautiful (or hideous) painting over the sofa?

Maybe. Often, though, more subtle factors underlie a room's appearance, almost subliminally influencing the way the space feels. Though among the most important elements of interior design, these are qualities the average person doesn't always think much about or even notice. The light that casts a soft glow on architectural features ... or harsh shadows under facial features. The colors that play off each other ... or leave the space feeling vaguely chopped up. The arrangement that lets traffic and conversation flow ... or sets up awkward stumbling blocks. The accessories so distinctive they tell their own little story about the person who lives there ... or so minimalist the place could be a hotel room.

We sought expert advice from four designers and design teams, asking each to provide some of the secrets behind these elements of style. They suggested general principles for effective handling of light, color, functionality and personality in interior design, and provided quick tips for maximizing the impact of each. You can draw on their wisdom to design -- or tweak -- a room of your own (and remember, many designers are willing to provide consultations on small projects, such as choosing paint colors), or just to figure out why one person's home makes you want to settle in for a while, and another makes you perch stiffly on the edge of your chair and keep your coat handy.

Katy Read • 612-673-4583