This graph shows a comparison of a resistor biased circuit and a CCR biased circuit. The resistor biased circuit, in yellow, shows that the LEDs will turn on as soon as the forward voltage across the LEDs is achieved, and that the current through the LEDs is then directly proportional to the voltage across the resistor. A Low voltage gives a low current and a low light output.  A high voltage gives a high current, and a high light output. However a the voltage continues to increase, the LEDs have the potential to go into thermal runaway. The CCR biased circuit, in Magenta, shows that the LEDs will also turn on as soon as the forward voltage across the LEDs is reached, the current then increases rapidly as the voltage increases and then stabilizes at the control current of 25 mA and remains constant regardless of the increasing voltage. The CCR circuit maintains constant LED brightness over a large voltage range and protects the LEDs as the voltage continues to rise.