Question

     Compare and contrast photopic and scotopic vision.  Discuss at least four of their differences. Remember to identify 4 DISTINCT differences each between the 2 vision systems.

Answer 1

• 1.Photopic vision is the vsion under well-lit conditions, which provides for color perception, and which functions primarily due to cone cells in the eye.
• Scotopic vision is the monochromatic vision in very low light, which functions primarily due to rod cells in the eye.It uses only rods to see,meaning that the object is visible,but only in black and white.
• 2.Photopic measurements favor “warmer” light, such as the orange light produced by common HID street light sources, including high pressure sodium lamps. Scotopic measurements are more representative of a broader spectrum of light, including the “cooler” light generated by most LEDs used in street lighting application.
• 3.Daytime is the domain of photopic vision, but nighttime is when our scotopic vision comes to the forefront.
• 4.In photopic vision,the combined peak sensitivity of the cones is at 555 nm, in the yellow-green part of the visible spectrum.And in scotopic vision,the peak sensitivity of the rods is at 507 nm, in the blue-green part of the visible spectrum.
• In general, the photometric quantities of light sources are measured as one normally functions under normal lighting conditions. Scotopic quantities of light sources may be given by an S/P ratio: the ratio between the photopic and scotopic values of a light source. Once the output of the light source is known for both scotopic and photopic conditions, the scotopic output of a light source can be measured when measuring its photopic value.