Abstract: A pigtail light string is provided for using in a conventional light string. The pigtail light string includes a conductive line connecting at least two or more light modules in parallel. The light modules includes LEDs of at least two colors and a control circuit board for generating different lighting patterns, such as colors, brightness, duration, and so on. Each light module is enclosed in a translucent decorative shell. One end of the conductive line is attached to a power plug for plugging into a socket of a light bulb on a conventional light string. The shape of the power plug is that of the base of a bulb used in a conventional light string so that the pigtail light string can be plugged into a socket for receiving a bulb on a conventional light string. When used in combination with conventional light strings, the pigtail light string provides a wider range of light change patterns as well as various decorative styles.