Experimental and theoretical investigation of optical transmittance in light-transmitting concrete

Light-transmitting concrete (LTC) is a cement-based composite that incorporates optical fibers to allow light transmission through cementitious composites elements, enabling architectural lighting. Despite growing interest in its optical performance, LTC lacks standardized procedures for measuring light transmittance, particularly concerning the distance between the specimen and the photodetector. This study addresses this gap by introducing a physical model based on a super-Gaussian intensity distribution to describe the light behavior emitted from embedded optical fibers. The model is validated through experimental tests using 5 cm cubic LTC specimens with up to 16 fibers and detector distances from 1 to 20 cm. The results reveal a nonlinear relationship between detector distance and measured transmittance, with an optimal detection distance observed around 5 cm for the investigated configurations. Specifically, for the 16-fiber configuration, the peak transmittance reached 0.33% at the optimal distance, which is higher than the 0.23% recorded at 1 cm or the 0.17% at 20 cm. Based on these findings, a practical predictive rule is proposed, linking this optimum to the fiber’s numerical aperture and the specimen’s dimensions. By providing a physically grounded framework for reliable optical transmittance measurements, the proposed approach highlights the potential of LTC for use in functional and smart concrete systems. Moreover, it contributes to the standardization of measurement procedures, enabling more consistent and reproducible evaluations of LTC performance in both research and industrial contexts.