Vision , visualizing or seeing is an act of eye and brain together. Human being visualize an object in two processes, Vision & Mental. Vision process is done by eye consisting of three abilities of eye ; Acuity , Accommodation & Adaptation. Acuity is the ability of eye to measure accuracy of vision. Acuity lets eye to see detail regulating or controlling lights. The more the light is the better the acuity or vision is. Accommodation is the outcome of muscular functioning of Lens & Iris together to able eye to focus on an object. While, with the ability of Adaption eye adjust itself to different lighting levels. The eye functions over a wide range of light levels and could cope with differences of brightness. Although very high brightness levels may cause blindness due to glare, there will be loss of detail at low light levels. An adjustment from low to high brightness is completed in seconds, but reverse takes minutes. At very high brightness levels there may be some blindness due to glare, and there may be some loss of details at low levels. Eye tends to adjust to the area of highest brightness within the field of view. When a person first enters in to a dark room his or her vision will be poor because of the CONES can't see, but with the RODS taking over the vision will be clearer. Brain does the mental process of visualisation. Brain is the essential part of vision. We can't see anything without brain. Brain, indeed process the data and information fed by eye to let us see or visualise eventually. The region of brain responsible for sight has the area corresponding to the FOVEA and a much smaller area devoted to the PERIPHERY. The images on the RETINA are inverted and transferred left to right and the correction made by the brain. Now, if the brain is upset in any way it makes incorrect interpretations of the data received. Most of the phenomena modify color takes place in brain not in the eye. The way in which we see a surface is largely depend of the intensity and wavelengths of the light it reflects, although nature of the light source may change the appearance of color. We don't have to look at a light source to idea on a an environment, bright or dim, we could idea on same by the appearance of the objects within the field of view. The brain records a image or scene almost simultaneously with actual sighting, but when two lights are flashed together, the one seen by FOVEA appear to flash ahead of what seen by PERIPHERY. The brain is slower in picking up Blue light since eye finds it difficult to focus [ Accommodation ability of eye . Blue lights used in police cars require a lower flashing rate than other colors to let them see clearly.