What is light: light: a wave; stream of photons, tiny particles that each consist of one quantum of energy. No such thing as light; is our perception to differentiate wavelengths. Light can be: absorption: energy that"s taken up, transformed to other forms of energy, transmission: convey light from one place to another through a transparent medium, reflection: energy that"s redirected when it strikes a surface (ex. When density is changed, reflection takes place. The smaller the pupil, the blurrier the vision: refraction: energy that"s altered as it passes into another medium (ex. Most relevant for vision; used to keep lens" image in retina focused. Plants evolved to tell if food is edible. Riping of apples: green not ready; can cause diarrhea. Mammals were small in dinosaur period: had stronger smell and hearing to survive. Vision became dominant after dinosaurs disappeared and mammals could roam in. Inner clock is based on light; when to sleep (ex.