White light source towards spectrum tunable lighting — A review

CIE standard illuminants are important for testing, calibration, printing quality testing, spices color testing and other photometric and calorimetric applications. Currently, fluorescent light sources represent these illuminants giving fixed and broad illumination spectra. Installation of all fluorescent illuminants in a light booth for testing and calibration of light sources becomes difficult and costly. LEDs with their efficient color changing capability can replace all the fluorescent illuminants by a single LED light source producing tunable illumination spectra saving lot of space, cost and power. Implementation of all the standard illuminants with LEDs with an optimum value of CRI and lumen efficacy is a challenging task. Proper control strategies are required to control the peak wavelength shifts for white point stability against junction temperature variations. This review paper highlights the characteristics of a white light source with all the various methods that can be used for controlling junction temperature and selecting an optimal set of LEDs for spectrum tunable lighting.