Light transport simulation in reflective displays



Journal Title

Journal ISSN

Volume Title



In the last several years, reflective displays have gained substantial popularity in mobile devices such as e-readers, because of their significant advantages in power consumption and sunlight readability. A typical reflective display consists of a stack of optical layers. Accurate and efficient simulation of light transport in these layers provides valuable information for optical design and analysis. Physically based ray tracing algorithms are able to produce simulation results that mirror the real world display performance in a wide range of illumination conditions, viewing angles, and distances. These simulation outcomes help system architects make far reaching decisions as early as possible in the design process. In this dissertation, a reflective display is modeled as a layered material, with a FOS (front of screen) layer on the top, a diffusive layer (diffuser) underneath the FOS, a transparent layer (glass) in the middle, and a wavelength-dependent reflective layer (pixel array) at the bottom. A set of simple and efficient spectral functions is developed to model the reflectance and absorption of FOS. A novel hybrid approach combining both spectro-radiometer based and imaging based measurement methods is developed to acquire high resolution reflectance data in both angular and spectral domains. A BTDF (bidirectional transmittance distribution function) is generated from the measured data to model the diffuser. A wavelength dependent BRDF (bidirectional reflectance distribution function) is used to model the pixels. Realistic light transport simulation requires interplay of three factors: surface geometry, lighting, and material reflectance. Monte Carlo ray tracing methods are used to link these factors together. Path tracing is employed to provide unbiased results. Stratified sampling and importance sampling are used for effective variance reduction. Stratified sampling produces well distributed random samples, and importance sampling helps Monte Carlo simulation converge more quickly. Different importance sampling methods are compared and analyzed. Simulation results of display performance, including reflectance, color gamut, contrast ratio, and daylight readability, are presented. The impact of different lighting conditions, diffusers, and FOS designs are studied. Measurement data and physically based analyses are used to confirm the validity of the simulation tool. The simulation tool provides the desired accuracy and predictability for display design in a wide range of lighting conditions, which makes it a valuable mechanism for display designers to find the optimal solution for real world applications.