There is another option. "Packets" of light are redshifted because the higher frequencies dissipate faster;

http://fqxi.org/data/forum-attachments/2008CChristov_WaveMotion_45_154_EvolutionWavePackets.pdf

The deeper implication would be that we are sampling a wave front, not detecting individual photons, having traveled billions of light-years, so the quantification of light would be a function of its absorption and measurement, not foundational to the light itself;

http://fqxi.org/data/essay-contest-files/Reiter_challenge2.pdf