In the context of radiative energy transfer, the integral, $\text{Math input error}$, which measures the overlap of the emission spectrum of the excited donor, D, and the absorption spectrum of the ground state acceptor, A; $f_{\text{D}}^{{}^{\prime }}$ is the measured normalized emission of D, $f_{\text{D}}^{{}^{\prime }}=\frac{f_{\text{D}}\left(\sigma \right)}{{\int }_0^{\mathrm{\infty }}{f}_{\text{D}}\left(\sigma \right)\mathrm{d}\sigma }$, $f_{\text{D}}(\sigma )$ is the photon exitance of the donor at wavenumber $\sigma$, and $\text{Math input error}$ is the decadic molar absorption coefficient of A at wavenumber $\sigma$. In the context of Förster excitation transfer, $J$ is given by: $$\text{Math input error}$$ In the context of Dexter excitation transfer, $J$ is given by: $$\text{Math input error}$$ In this case $f_{\text{D}}$ and $\text{Math input error}$, the emission spectrum of donor and absorption spectrum of acceptor, respectively, are both normalized to unity, so that the rate constant for energy transfer, $k_{\text{ET}}$, is independent of the oscillator strength of both transitions (contrast to Förster mechanism).