**1.2 Solid-state lighting (SSL)**

Solid-state lighting (SSL) is a technology in which semiconductor material converts electricity into visible light [10]. Such technology produces visible light utilizing the principle of electroluminescence (EL). EL is a phenomenon in which semiconductors emit light when an electric current pass through them. SSL technology generates visible light with reduced heat generation and less energy dissipation as compared to the traditional lighting sources. Over the past few years, SSL attracted much attention for general lighting than conventional light sources due to their advantages: small size, long lifetime, lower energy consumption, high efficiency, high color rendering index, high luminous efficacy, and environmental friendliness. According to the U.S. Department of Energy (DOE), by 2035, SSL will penetrate over 90% market and reduce lighting energy consumption by 75% [10].
