A yellow point wins. Against a dark field, two stars assigned the same bolometric luminosity can refuse to look equal: the yellow source places more of its spectral power distribution near wavelengths where human vision extracts its strongest signal, while blue radiation falls in a less favored portion of the eye's response curve. Physics has not cheated; perception has priced the output differently.
Photometry makes it plain. Under photopic vision, the standard luminous-efficiency function peaks near green-yellow wavelengths, close to 555 nanometers; radiation near that peak produces more lumens per watt than radiation in blue bands. Equal watts mislead. Luminous flux is a weighted measurement, not a neutral energy ledger. Astronomers separate visual magnitude from bolometric luminosity for this reason: a blue star may be hotter, with substantial output at shorter wavelengths, while cone cells assign its visible photons less weight.
Context can reverse the verdict. In dim conditions, scotopic vision shifts sensitivity toward blue-green light through rod cells, so a source's apparent advantage changes; atmospheric extinction, distance, filter choice, and the detector used can also alter the comparison. A telescope sensor does not share the retina's preference. Yet in ordinary bright viewing, lumens rather than raw watts describe what the eye calls bright. Two equal furnaces, one yellow and one blue, meet the observer not as equals, but as different bargains struck by biology.
