The present invention provides a flexible light emitter driver circuit which adjusts the luminance of the light emitter diodes (LED) by a manual input signal. The light emitter driver circuit comprises a Duty Ratio Change Logic, a PWM Generate and Control Logic, an oscillator, and a gate driver. The Duty Ratio Change Logic adjusts the duty cycle of the output signal according to the manual input signal. The PWM Generate and Control Logic generates a PWM signal according to the output signal to control the current of the LED, thus adjusts the luminance of the LED. The present invention further provides a highly flexible display system that comprises a light emitter driver circuit which can adjust the LED luminance by manual input signal.