  Photoinduced biological processes occur via one photon absorption in natural
light, which is weak, CW and incoherent, but are often studied in the
laboratory using pulsed coherent light. Here we compare the response of a
molecule to these two very different sources within a quantized radiation field
picture. The latter is shown to induce coherent time evolution in the molecule,
whereas the former does not. As a result, the coherent time dependence observed
in the laboratory experiments will not be relevant to the natural biological
process. Emphasis is placed on resolving confusions regarding this issue that
are shown to arise from aspects of quantum measurement and from a lack of
appreciation of the proper description of the absorbed photon.
