Y-axis is the proportion of light absorbed by rhodopsin (rods) at each wavelength indicated on the x-axis. Remember that at the retina, light has to be absorbed in order to have an effect. CRUCIAL FACT:A single receptor (rod here, same for cones) is triggered by amount of light energy, which, roughly is the absorption value on the y-axis TIMES the amount of light at the wavelength.

Number of incident photons is an Independent variable Important column. These numbers = proportion x number of photons Number of incident photons is an Independent variable # Incident Photons Proportion Percent # absorbed for 1000 # incident photons # absorbed for 2000 1000 0.01 1 10 2000 20 0.02 2 40 0.03 3 30 60 0.04 4 80 0.05 5 50 100 0.06 6 120 0.07 7 70 140 0.08 8 160 0.09 9 90 180 0.1 200

Simplest light/color matching experiment to illustrate psychological consequences of a single sensitive pigment operating. Standard Variable --- brightness varies, wavelength stays the same. Question for observer: Do the two lights look identical? (Same) or not (Different)? Adjust brightness (amount of light) in variable light. Lighter than before -- can make this lighter or darker. Keep asking if the two lights look identical or not.

Use the arrow keys to toggle through a small sample of brightness variations in the variable light. Standard --- One fixed wavelength for and experimental trial Variable --- Also one wavelength, but a different one from the standard In this kind of matching experiment, one light stays the same and one light changes brightness (amount of light energy). As the brightness of the variable light changes, the wavelength stays the same.

Visual pigments In rods and cones