Density is not the energy of the whole packet
Radiation energy density changes by q², but the volume of the same moving light complex on a simultaneous slice changes by 1/q. Its total energy therefore changes by q, just like frequency.
Read · Special relativity: from clock operations to electrodynamics · Results
§8 · finite light energy and moving mirrors
Follow the introduction and all ten sections, including field transformations, finite light complexes, moving mirrors, charge-current transformations, and the electron-force conventions.
Newly authored explanatory preview in modern notation, with editorial and physics review pending. Both the kinematic and electrodynamic halves are treated, but this is not a German transcription, an aligned translation, or a complete critical edition. The source paragraphs, footnotes, acknowledgment, and date-lines are not claimed to be fully represented or reviewed here. Headings and argument units are editorial.
Reflection starts with interception
Transform into the mirror’s rest frame, reflect there, and transform back. First check that the light catches the surface: its normal speed must exceed the mirror’s receding speed.