Improvement of color rendering index of BGYR laser illuminants

Laser-driven phosphor conversion (PC)-type white light sources are receiving a great deal of attention in next-generation high-intensity lighting and display technologies. Laser lighting is attracting attention for its functions, such as energy saving and light distribution control. However, the PC-type white light source has problems with color control and thermal quenching. Thus, monochromatic light mixed- or color mixed (CM)-type white light sources are promising, but there is a problem with their color rendering properties. We investigated the CM-type white light sources that mix four colors (blue, green, yellow, and red). We have improved the color rendering index (CRI) of a four-color mixed laser. By maximizing the value through combining the wavelength of four colors and each laser output ratio, the average CRI Ra and the special CRI R9 can be obtained when the color temperature used in general lighting is approximately 5000 K. The color rendering property was predicted by the combination of laser output ratios, and a light source with an Ra of 80 or more and R9 of 94 was obtained experimentally. At the same time, we were able to demonstrate the high luminous efficacy of radiation.