By primary photochemistry, we mean conversion of light (or excitation) energy into redox chemical energy that is then stored to do useful work.
(we; mean; conversion of light (or excitation) energy) (redox chemical energy; is stored; to do useful work; T:then) (redox chemical energy; to do; useful work)
we redox chemical energy redox chemical energy
mean is stored to do
conversion of light (or excitation) energy
to do useful work T:then
useful work