**4. Laser diode-based solid-state lighting**

Blue GaN LD is an emerging candidate in the future high-luminance SSL because of its advantages over the LED and traditional lighting sources. The higher efficiency of LD at higher current densities makes LD an alternative promising excitation source for higher-luminance SSL application. The LD light source has the potential to generate more efficient white light as compared to LED. LD has high coherence, high power per unit area, and narrow spectral width. Recently the attention of the researchers shifted towards LD-based phosphor-converted white light source. Different types of phosphor films have been previously reported to generate LD-based white light in SSL. For example, in 2008, Xu Yun et al. generated a UV GaN LD-based white light source of 5.7 lm with a CRI of 70and a CCT of 5200 K by using strontium halophosphate activated with divalent europium as a blue phosphor, and a YAG as a yellow phosphor [12]. In 2009, the same research group generated white light of 3.6 lm with CCT of 5393 by exciting near-UV laser diode on red-, green-, and blue-emitting phosphors [13]. In 2010, white light emission of 5 lm with an efficacy of 10 lm/W by exciting 445 nm blue LD on Eu-doped silicate [ ( ) <sup>2</sup> BaSr SiO : Eu <sup>2</sup> <sup>4</sup> <sup>+</sup> ] yellow phosphor is reported [14]. Kristin et al. generated a white light of 252 lm with a CCT of 400 K and a CRI of 57 using blue LD in combination with yellow-emitting cerium-substituted yttrium aluminum garnet (YAG: Ce) [15].
