Rods can respond to light but also to pressure.
Voltage can set off most receptors. Works very well with touch receptors not as well with more diffuse receptors such as pain. Touch Receptors can adapt to a stimulus - put an ear ring on pretty soon you don't know it is there. Light comes through the pupil. When examining something close, the cillary muscle are contacted relaxing the zonular fibers which allows the lens to become more spherical.