Lighting Research

High performance LED lighting requires judicious considerations in LED package designs, circuit topologies, LED lumen outputs, power dissipation, color, and lifetime. These are strongly dependent on a number of manufacturing and design elements. Optical, electrical, and thermal management of LED arrays are still poorly understood, yet vital to overall lighting efficiency and performance. Thus we will make extensive efforts in design, component characterization and system engineering to ensure that the lighting performance meets the intended application needs. Our experience in LED lighting system design and technology transition to the lighting industry, as well as deep understanding of lighting science will be utilized for lighting technology development in conjunction with communication system design.

Lighting, in our context, has to be designed in conjunction with communication and navigation. The lighting and communication functionalities are well linked through LED driver design and spatial distribution of LEDs. A driver must accommodate non-overheated lighting, optional dimming and flicker-free requirements. Meanwhile, as optical communication transmitters, LEDs should be able to impart communication data with a large dynamic range of data rate. During normal lighting, LED drivers may be constant voltage types (such as 10V, 12V and 24V) or constant current types (like 350mA, 700mA and 1A). When dimming, drivers typically use pulse width modulation (PWM) to regulate the amount of power to the LEDs. This technique turns the LEDs on and off at high frequency, varying the total “on” time to achieve perceived dimming. Driver output frequency should be large enough to avoid perceptible flicker throughout their full dimming range under typical circumstances. In accordance with these requirements, we will also design proper communication coding techniques jointly with driver design to avoid low frequency signals when pulsed data modulation is used or optimize parameter settings when OFDM is adopted.

In indoor settings as an example, the spatial distribution of LEDs can mostly fulfill both lighting and communication requirements. The ceiling-mounted LED array normally will be optimized for lighting purposes, producing uniform illumination with soft shadows. In fact this ensures at least minimal non-line of sight communication links from the ceiling to any spot within the coverage. Thus a portable communication terminal expects to receive sufficiently strong signals from one or more light sources, most likely under line of sight scenarios. However, pulse broadening due to diffusion or beam divergence is an adverse factor to communication speed. Among all possible best lighting settings, we will optimize for communications. Meanwhile, we will apply advanced communication techniques to tackle pulse spreading.