*4.1.1 Efficiency*

LED is an excellent energy-efficient light source for artificial lighting applications. Despite the outstanding achievement, LED still has drawbacks. The efficiency of LED drops at high current densities, limiting the luminous flux per unit area of an LED chip. The comparison of efficiency versus input current density

#### **Figure 2.**

*(a) The comparison of the efficiency versus input current density between state-of-the-art and future LEDs and LDs. (b) The comparison of the area of PC-LED and PC-LD phosphor film [16].*
