transmittedlight

Transmitted light refers to the portion of incident light that passes through a material or interface. When light encounters a boundary or travels through a medium, some of it may be reflected or absorbed, and the remainder is transmitted. The transmitted light is commonly described by transmittance, T, defined as the ratio of transmitted intensity to incident intensity (I_t / I_i), and it can be expressed as a function of wavelength in a transmittance spectrum. In a homogeneous absorbing medium, transmitted intensity is often described by the Beer-Lambert law: I_t = I_0 e^{-αx}, where α is the absorption coefficient and x is the path length; in practice, scattering and surface reflection also reduce transmission.

Material transparency is categorized by optical clarity: transparent materials transmit most light with minimal scattering, translucent materials transmit light but scatter it, and opaque materials transmit little or none. Transmission is influenced by the material’s refractive index, absorption properties, and microstructure. At interfaces, transmitted light changes direction according to Snell’s law, and the transmission angle depends on the refractive indices of the media. When light travels from a denser to a rarer medium, there is a critical angle beyond which total internal reflection occurs, preventing transmission beyond the boundary.

Applications and measurement: Transmitted light is central to imaging, spectroscopy, and photography, where it enables viewing through lenses and samples. In coatings and optical filters, transmission is controlled to shape spectral output. Spectrophotometers measure transmittance as a function of wavelength to characterize materials. In fiber optics, high transmission through guided cores enables communication, while in solar energy, transmitted and absorbed light within active layers affects efficiency. Diffuse transmission occurs when scattering dominates, whereas specular transmission occurs through smooth, unscattered interfaces.