Abstract: A traffic light forms a yellow light by blending a red light and a green light according to the color blending principle. Red and green light emitting diodes are provided for showing the red, green, or yellow light. The traffic light comprises red-green light emitting diodes mounted on a substrate, wherein each one of the red-green light emitting diodes comprises a red and a green light emitting chip packaged in a plastic casing. A power source transforming circuit is mounted on the substrate for electrically conducting the red and the green light emitting chips respectively when it is desired to show a red light and a green light respectively, and for electrically conducting the red and green light emitting chips simultaneously when it is desired to show a yellow light. Accordingly, a single set of light source can show red, green, or yellow light so its production cost is reduced.