Light-induced motion is of increasing importance in materials development. In many situations, modelling the detailed dynamics of light-induced phenomena is not practical, yet a description of the behaviour is needed. We attempt to show here that in some such situations, symmetry arguments can prove useful. We outline a simple scheme where symmetry arguments can be useful in modelling the dynamics, and show, in three examples, that in some instances, light intensity may be regarded as a mechanical potential. Such an approach may help in understanding photoactuations in situations where more detailed analyses are impractical.