CHAPTER 10 ■ LEDSA bond wire (also called a whisker) connects the die to the anode lead. The bond wire is very thin! With
some clear LEDs, you can actually see the shadow of that wire (and sometimes the shape of the die) when
you aim the LED at the ceiling.
Identifying Multicolor LEDs
Placing more than one die into an LED allows it to emit more than one color (see Figure 10-11). The lens
is usually water-clear or white-diffused, because it wouldn’t make much sense to tint the lens with a single
color for an LED that can display two or more colors.
Multicolor LEDs are useful for conserving space or for showing multiple statuses. For example: white is
off, red is error, green is ready.
Bicolor
Bicolor usually refers to a multicolor LED that has two leads. When the electricity flows in one direction,
the LED lights with one color. When the electricity flows in the other direction, the LED lights with the
other color.
Since electricity can’t flow in opposite directions at the same time, only one color can be lit at a time.
However, you can switch the flow back and forth really quickly. To human eyes, the result will be a third
color that is a mix of the first two.
Tricolor or Tri-state
Tricolor usually refers to a multicolor LED that has three leads, instead of two (refer back to Figure 10-11).
One lead for the first color, another lead for the second color, and a third lead that they share. If they share
the cathode (-), it’s called common cathode. If they share the anode (+), it’s called common anode.
Figure 10-11. Side view of a two-color (red and green) tri-state LED