History of solid-state light sources

Abstract

The second decade of the twenty-first century has become the period when light-emitting diodes (LEDs) are beginning to reach their promise of being the dom inant technology for generating light. For those who have worked in this field, it is gratifying to see the enthusiasm of consumers for the technology and how the rate of adoption often outpaces expert projections. At the time of writing, leading manufacturers of lighting products achieve more than 40 % of their revenue by sales of products that use LEDs as the light source, and this portion is projected to be over 80 % by 2020. The rapid adoption of LEDs is largely due to the tremendous improvement in underlining technology which enabled cost reduc tions and increase in functionality of lighting systems. As novel as LEDs may seem, the related discoveries and technology development have over a century-long history, with generations of researchers working on fundamental exploration without which the present day successes would not have been possible. At the same time, the present state of the art of LED technology and manufacturing lacks the homogeneity of the more established fields such as conventional light sources or silicon integrated circuits. This chapter will review the pioneering work, with more focus given to the developments of the most recent decades. An outlook to the directions that the field may take will be provided as well.