Light Adaptation

Question 1

Light adaptation

Answer 1

The decrease in visual sensitivity that occurs with increased levels of ambient illumination.

Question 2

The changes during light adaptation that I’ve the observer visual function

Answer 2

1. Constriction of pupil
2. Decreased sensitivity of photoreceptors
3. Decreasing dominance of rod activity with increasing ambient light. (shift from 507 to 555nm wavelength)

Question 3

Cone dystrophy

Answer 3

Inherited retinal disorder characterized predominantly by the loss of cones.

Results in decreased best-corrected VAs, poor color perception and sensitivity to lights (photophobic)

Ability to adapt to light is impaired.

Question 4

What does the Devries-Rose law describe

Answer 4

At very low light levels, our threshold for detecting luminance differences is determined by quantum fluctuations of the background.

Question 5

What does Weber’s law describe

Answer 5

At high light levels, our threshold for detecting luminance differences is determined by many factors. Weber’s law shows us that the visual system was built to distinguish objects from their background- to detect contrast. Our ability to detect contrast remains the same over a wide range of background luminances.

Question 6

The difference needed between the target and the background luminance to just detect the target reliably is proportional to

Answer 6

the square root of the background light.

Question 7

Weber’s law: On log-log coordinates, if the slope is 1.0, then when the data is polluted on linear coordinates, the resulting function will be a

Answer 7

line

Question 8

Weber’s law says that our ability to detect contrast remains the same over a wide range of

Answer 8

Background luminances.

Additional light falling onto projection charts can reduce contrast.

Question 9

Is the scotopic or photopic system more sensitive to contrast?

Answer 9

Photopic.

Which is why weber’s constant is smaller under photopic (0.015) vs scotopic (0.14).