Loi de Beer-Lambert

La loi de Beer-Lambert, aussi connue comme la loi de Beer-Lambert-Bouguer chez les Français et loi de Beer dans la littérature anglo-saxonne, est une relation empirique reliant l'atténuation d'un faisceau de lumière aux propriétés du milieu qu'il traverse et à l'épaisseur traversée. La loi de Beer-Lambert établit que l'absorbance A d'une solution est proportionnelle, d'une part, à sa concentration c et, d'autre part, à la longueur \ell du trajet parcouru par la lumière dans la solution : A=\varepsilon \ell c avec :

\varepsilon est une constante nommée absorptivité molaire ;
\ell est la longueur du trajet parcouru par la lumière dans le milieu considéré ;
c est la concentration de l'entité chimique absorbante.

La loi de Beer-Lambert est aussi valable pour décrire l'absorption de tout rayonnement (photons, neutrons, particules α) par la matière condensée et constitue une solution élément

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