**3.3 UV LD chip and RGB phosphor**

White light can be generated by using ultraviolet (UV)-LD to excites RGB emitting phosphors. The mixture of emitted blue, green, and red lights results in white light to human eyes. High CRI white light can be generated using this method because the red, green, and blue phosphors emission can cover the whole visible region. When the UV radiation is down-converted into the visible light, there is a large loss of energy, therefore the luminous efficacy of this scheme is low.
