With the recent advances in photobiology research and light-emitting diode technology, considering the circadian effects and the potential health benefits of lighting has attracted much attention. In this work, to achieve a white light-emitting LED cluster with beneficial and tunable circadian effects, a red-green-blue-warm white colour-mixing method based on pulse width modulation has been introduced and developed. Five optimal spectral power distributions were achieved with the correlated colour temperatures of 2700, 4000, 5000, 6500 and 8000 K that provide maximum colour-rendering indices of 95.0, 96.6, 96.8, 95.6 and 93.5 for each correlated colour temperature. Moreover, the Bellia model was modified to take into account the reduction in spectral transmittance of the human eye that occurs with age. Using the five spectral power distributions, based on the eye spectral transmittance with age-related change, we studied the change of the circadian effect with corneal illuminance at the different correlated colour temperatures. Solutions are provided for scenarios where circadian effect should be avoided for different age groups while the reasonable illuminance and colour temperature are maintained.