A 1-carat radiant-cut diamond is one of the best choices to make for its fire and brilliance. The facets return consistent light across the diamond, making it shine superbly. A radiant diamond should have no dead spots to make its sparkle dull. To get an ideal 1-carat radiant-cut diamond, look for even faceting and a depth of 61% and 69% and a length-to-width ratio of 1.00 to 1.05 for a squarish look and a ratio between 1.05 and 1.15 for a rectangular look.