Luminous Efficacy and Improvement of White LEDs for Lighting(<Special Issue>Special Topic on LED Lighting -LED Lighting of Today and the Future-)

Luminous efficacy of white LED has been improving rapidly in the past decade. Now, extremely high efficacy of around 150lm/W is reported in the latest research. Superior performance than other conventional devices was achieved at last, and then practical lighting products like LED-bulbs was launched on the market. It is expected that these new products contribute to energy saving and carbon reduction as green devices. This article reviews technical progress and future possibility of which each factor connected to improvement of luminous efficacy.