Multi-LED colour mixing light sources are increasingly being used in lighting. The method used to set the dimming signal needs to accurately achieve and sustain the desired colour temperature and high colour rendering index (CRI). A pulse width modulation (PWM) signal is always used in LED colour mixing. But the PWM switch state creates a time delay in the multi-LED current regulator, resulting in a colour difference. A modified PWM signal to accurately maintain the desired colour temperature and a high CRI is derived from a parameterised LED current regulator switch state, using curve fitting. The modified PWM signal can be calculated from reconstructed coefficients of the illuminant spectrum.
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