= Stellar energy-generation rate
{title2=$\epsilon$}
The <stellar energy-generation rate>, $\epsilon$, is power supplied per unit <mass>, conventionally measured in $\mathrm{W\,kg^{-1}}$. In a stationary spherical model with specified local net sources,
$$
\frac{dL_r}{dr}=4\pi r^2\rho\epsilon,\qquad \frac{dL_r}{dm}=\epsilon.
$$
Here $L_r$ is the <luminosity> crossing a sphere and $dm=4\pi r^2\rho\,dr$ is its shell <mass>. A localized source therefore increases the outward <luminosity> across that shell.
The convention must say whether $\epsilon$ includes losses such as <stellar neutrino energy loss>. During <stellar evolution>, changing internal energy and contraction add terms to the full energy equation. A high nuclear reaction rate does not necessarily equal immediately escaping surface light: energy must still be transported through the <stellar structure>.
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