The use of highly efficient semiconductor light-emitting diodes (LEDs) suitable for illumination applications has been shown to potentially enable huge energy savings, a strong reduction in green-house gas emissions, and a reduction of environmental pollution. High luminous source efficiencies (300 lm/W) and high color-rendering indices (CRIs of 90) would be feasible with ideal solid-state sources. This talk discusses several critical issues in solid-state lighting and opportunities based on innovative technologies to overcome the limitations encountered by the technical community.
The following innovative solutions to current device-performance limitations will be presented: In the field of nano-materials, we will present a new class of optical thin-film materials, low-refractive-index materials, with a very low refractive index, close to that of air. The low-n materials are based on highly porous nano-rod arrays of SiO2 that are fabricated by oblique-angle evaporation. This material offers an opportunity to improve optical components such as reflectors, filters, microcavities, and photonic crystals. Furthermore, a triple-layer omni-directional reflector (ODR) is presented that exhibits a very low mirror loss, two orders of magnitude lower than that of conventional metal and distributed Bragg reflectors (DBRs). The ODR is expected to allow for larger chip sizes without incurring an area-scaling penalty. We will also present results on white LEDs with remote phosphor distributions. Such phosphor distributions offer higher efficiency than conventional proximate phosphor distributions.
Solid-state sources based on LEDs have advantages not offered by conventional light sources, namely controllability and adaptability. In contrast to conventional incandescent and fluorescent sources, future smart light sources based on LEDs offer control of spectral composition, polarization, color temperature, temporal modulation, and spatio-chromatic emission pattern. Challenges and opportunities arising from enhanced controllability will be discussed.