Daylighting a space is both an art and a science. The impact of daylight can make a building's design come to life. Daylighting can be carried out skillfully, or it can be too casually considered or totally misunderstood. Bad daylighting is devastating to a space and costly to fix. Today, in this era of sustainable design, daylighting is given more consideration than ever. One of the desirable attributes of daylighting is its significant role in creating the mood or atmosphere of a space. It affects the comfort, productivity, performance, health and well-being of occupants. Daylighting has a significant influence on energy efficiency, electrical lighting costs and HVAC climate control. And of course, the green movement and desirability of earning LEED points increasingly inform the daylighting plans for buildings. Too often, designers don't comprehend the result of a daylight scheme until construction is completed, the space occupied, and all the money spent. This is the wrong time to discover glare, over-bright areas, shadows, dark spaces or poorly balanced light levels. Effective daylighting, one of the most powerful tools available to architects, should be planned in the design phase. This article discusses the benefits of daylight modeling--a site-specific simulation that aids the process of intelligent daylighting design. Just as traditional miniature, scale-model building and 3-D computer modeling help represent what a finished design will look like, climate-based daylight simulation demonstrates clearly the impact of the size, type and placement of skylights, windows or translucent wall systems. Results can be compared and changes made in the early design stages before final recommendations are made. Using computer-generated charts and light-level schematics, daylight modeling simulates the effects of daylighting and enables designers to analyze the behavior of light within the space. Using daylight modeling, "what if" scenarios can be considered and demonstrated; pre-planning can manage and eliminate all of the negatives. Alternative design solutions can be studied and planned. Spaces can be analyzed for a certain time of day or season, as solar angles change, or evaluated for overall annual performance using local climate conditions. Daylight modeling shows the way to better illuminate any space and eliminates costly design mistakes. (Contains 2 figures.)