Bi-color LED 3mm Red Green LED Common Cathode 

- Bi-Color LED Lamps - 309ERLGWD-10 The reason why Bi-color LED emits two colors is that two chips are packaged in the same bracket. It's kind of like the combination of Red Through-hole LED(625nm LED) and Green Through-hole LED(520nm LED). How to control the color of Bi-color LED Lamps? For LED Lamps (or DIP LED) type, there will have 3 pins bi-color LED and 2 pins bi-color LED. The 3 pins throuhg-hole LED will also have common cathode and common and anode. This 309ERLGWD-10 are the kind of 3 pins LED and with common cathode. To distinguish between anode and cathode, we mainly look at the positive and negative poles of the longest pin in the middle. If the pin in the middle is positive, it is anode; If it's negative, it's a common cathode. The current generally flows in from the positive electrode and out from the negative electrode.