To make sure the PLED does not activate while the LED is still healthy and active, the minimum breakdown voltage of the PLED must be higher than the maximum forward voltage of the LED.  Remember that the LED voltage is dependent on the brightness of the LED, the temperature of the LED, and the color of the LED. Notice that this is the parameter that changes with the different PLED-6, PLED-9 and PLED-13 packages. The second parameter of interest is the maximum breakdown voltage. It is important that this value be less than the compliance voltage of the LED power supply. If it is not, the PLED device may not activate when the LED fails open because the power supply cannot break down the PLED device. Finally, all PLED devices are rated for continuous use at 1A of current. This rating is actually achieved with no additional heat sink or extended copper PC board traces required, making the PLED one of the most robust devices in the market. Finally, the data sheet shows an equivalent circuit that appears to work in only one direction. In fact, all of the PLED devices have two of these circuits wired in an anti-parallel configuration. This means that the PLED device is bidirectional and can be installed into the LED circuit without regard to polarity.