A lighting plan is the unsung hero of interior design. The same room with bad lighting feels flat; with thoughtful lighting it transforms. Most rooms need three layers: ambient (overall illumination — usually a ceiling fixture or recessed cans), task (focused light where you do things — reading lamp, desk light, kitchen under-cabinet), and accent (highlights for art or architectural features — picture lights, narrow-beam spots).
Good lighting plans control more than fixture placement. They specify color temperature (warm 2700K for living spaces, cooler 3000-3500K for kitchens and baths, never daylight 5000K+ in residential except for task work), beam angle (narrow for accent, wide for ambient), and dimmability (almost everything should dim — a room's mood shifts dramatically across the dimming range).
The most common residential lighting mistake is relying on a single overhead fixture for everything. Even adding a single floor lamp on a dimmer to a living room transforms the space.