Because bacteria are extremely small, the principles of optics prevent them from having lenses or other organs capable of determining the direction from which light is incident.  On the other hand, an entire spherical bacterium can potentially act as a lens, concentrating light from a given direction onto a corresponding position on the opposite side of the bacterium, and thus forming a very crude image.  Bacteria are certainly capable of responding to the frequency of incident light, if they contain molecules that selectively absorb light in specific frequency ranges.  And, they should be able to respond to the brightness or intensity of incident light, if those molecules return to their normal state shortly after absorbing a photon.  Of course, additional molecular machinery would need to be present in a bacterium to translate absorption of a photon into any sort of meaningful response.