Bipolar LED means those DIP LED(through-hole LED) that with two pins and two colors, which can be 5mm LED, 3mm LED or retangular LED, oval LED ect.
The emitting color of LED depends on the LED chip inside normally. In order to produce the bipolar LED that emits two different color, we need to put two kinds of chip inside the same cup.
For some chip, we can change it`s emitting color by the phosphor(liquid). Different phosphor will make different emitting color. For example, when we need the warm white color, we need to put the yellow phosphor on the top of blue chip. And when we need the pink emitting color, we need to put the pink phosphor on the top of blue chip. If we just need single color in the same LED Lamps, phosphor will work perfect in that case. But when we need two color in the same through-hole LED, which means we need to put two chips inside the cup and put two kinds of phosphor inside. It`s OK to put two chip inside the same cup, but the phosphor will mix together due to the phosphor is liquid. When we put red phosphor and yellow phosphor together, we will get orange phosphor at the end...then the phosphor will cover both of blue chip inside and emits the same color when we light it up.
But this bi-color LED with pink & white color do available in SMD LED type, because there have two cups inside of SMD LED case, which ensures that the two types of phosphor can act separately on the two chips.
