I. Introduction
Lighting systems based on LEDs are becoming the dominant lighting solution due to improved energy efficiency, better quality of light and longer life span. According to the European LED quality charter report, lighting accounts for 15 – 17 % of the total energy consumption [1]. Similarly, US energy information administration estimated the US residential and commercial sector used around 273 trillion Wh of electricity for lighting in 2017, or about 7 % of the total electricity consumed [2]. Globally, there are over 33 billion light sources spending 2650 trillion Wh of electrical energy per year, which is 20 % of the total global electricity production [3].