This reference design implements a five-segment LED smart stack light with 20 LEDs used in factory floor and industrial process automation of greater complexity. An IO-Link interface is implemented for controlling the stack light and reading back status information. The design features low power consumption to be powered through the IO-Link interface. This signal light reference design demonstrates how the power dissipation of the RGB LED driver can be reduced by 30% and the range of the brightness control can be extended. Automatic brightness control adapts the brightness to ambient light. The reference design uses a simple PWM to modify the output voltage of a switching regulator to implement dynamic headroom control.