C7 Light Bulbs are the smaller of the two most common Christmas Light Bulbs. They feature a candelabra base and look great indoors and out. All American Christmas Co. offers a variety of C7 Christmas lights, including Steady Burn, Twinkle, and Opaque bulbs. Like the name suggests, Steady Burn bulbs are constant on, while twinkle bulbs randomly flash. Opaque bulbs are the classic painted Christmas lights that offer a soft festive glow.