The term Protanopia refers to a form of colorblindness. It is a defect which is formed in connection with pigment sensitivity of human eyes. On the retina of human eye there are photoreceptors known as cones which are sensitive to colors. These are usually sensitive for red, green, or blue light in the human eye. When the pigment sensitivity per cone is reduced, or when any of the three cone systems is absent colorblindness occurs. The state of Protanopia reduces the brightness of red / orange / yellow. This dimming is evident when red may be confused with black or dark gray, and one cannot see red traffic lights.