Advanced color control for multicolor LED illumination systems with parametric optimization

Abstract

LED based luminaires are capable of providing innovative functionalities, such as color control and color temperature adaption. In fact, precise control of these two parameters has turned out to be very complex and challenging. This paper presents an advanced control technique for a very accurate and robust adjustment of both color and color temperature. Additionally, the proposed methodology enables system optimization of a LED based luminaire regarding various parameters, e.g. maximum color rendering index (CRI). The control signals for any PWM-switched LED driver can be tuned accordingly by the system controller. The algorithm is tested in simulations for three different luminaire realizations, namely RGB-W, RGB-A and RGB-CAW. The CIEDE2000 color difference formula is applied for computing the perceivable color difference ΔE by the human eye. The developed color control algorithm achieves a superior minimization of the absolute color distance to ΔE ≤ 0.21, which is not even perceivable by the human eye. This performance can be realized over a wide color temperature range from 3200K to 7500 K while luminous output is kept constant. Due to the applied optimization, a CRI of ≥ 90 can be maintained over the same color temperature range for all three scenarios. Simultaneously, the deviation of correlated color temperature ΔCCT is minimized to less than 50 K, which is a precision of more than 98 %. The novel algorithm considers strict hardware limitations, such as finite switching speed or limited computation resolution, to account for implementations on an ASIC or a μC.