C9 Christmas replacement bulbs are available in a variety of colors, shapes, sizes, and wattages. Popular colors include clear, red, blue, green, purple, pink, and orange. Popular shapes include faceted, smooth, and twinkle. Popular sizes include C9, C7, and C6. Popular wattages include 7 watt, 5 watt, and 3 watt. Many Christmas replacement bulbs are LED, which are more energy efficient than traditional incandescent bulbs.