Junichi KINOSHITA^*, Yoshihisa IKEDA, Yuji TAKEDA, Misaki UENO, Yoji KAWASAKI, Yoshiaki MATSUBA, and Atsushi HEIKE

R&D Center (Imabari Complex), Toshiba Lighting & Technology Corporation, Imabari, Ehime 794-8510, Japan

(Received May 30, 2012; Accepted August 31, 2012)

The speckle contrast of blue light emission out of high-brightness white lamps using phosphors excited by InGaN/GaN blue laser diodes is evaluated as a measure of coherence. As a result, speckle contrast of as low as 1.7%, the same level as a blue light emitting diode, is obtained. This implies that the original blue laser light can be converted into incoherent light through lamp structures without any dynamic mechanisms. This unique speckle-free performance is considered to be realized by multiple scattering inside the lamp structure, the multi-longitudinal mode operation of the blue laser diodes, and the use of multiple laser diodes. Such almost-incoherent white lamps can be applied for general lighting without any nuisance of speckle noise and should be categorized as lamps rather than lasers in terms of laser safety regulation.

Key words: speckle contrast, InGaN/GaN blue laser diodes, phosphor conversion, coherence, laser safety

^*E-mail address: junichi.kinoshita@tlt.co.jp