ABSTRACT
In degradation models it is assumed that a component fails when one of its functional parameters (power, voltage, light output etc) degrades enough that does not allow it to carry out its functionality successfully. Degradation failure is usually defined as a percentage of the nominal value from which the component is considered to be unable to perform its function. For example in LEDs case, the failure is considered when the light output falls below 70% of nominal value [2].
