Ljusabsorption

Light absorption is the process by which matter takes up incident photons, converting light energy into other forms such as heat or electronic excitations. The amount of light absorbed depends on wavelength, chemical composition, thickness (or concentration), and the structure of the material.

At the atomic or molecular level, absorption occurs when photon energy matches available transitions. Electronic transitions dominate in the ultraviolet and visible range, while vibrational transitions occur in the infrared and rotational transitions in the microwave. In solids, absorption can involve interband transitions, impurity states, lattice vibrations (phonons), or free-carrier absorption in metals. The result is an absorption spectrum that varies with wavelength and reflects the material’s electronic and vibrational structure.

Beer-Lambert law relates absorption to path length and concentration: A = εlc, where A is absorbance, ε is the molar extinction coefficient, l is the path length, and c is the concentration. Alternatively the transmitted intensity I = I0 e^(-αl) expresses the exponential attenuation of light with distance in the medium. These relations assume a homogeneous medium and, for solutions, dilute conditions.

Color arises from selective absorption: a material appears colored because it transmits or reflects the wavelengths it does not absorb, while absorbing others. Light absorption is central to spectroscopy, pigments and dyes, solar energy conversion, and atmospheric science. Factors such as temperature, pressure, impurities, and light intensity influence the extent and spectral pattern of absorption.