Under scotopic conditions, the Stiles-Crawford effect shows what?

• A. Greater magnitude
• B. No difference
• C. Smaller effect
• D. Not present

Answer: (B)

The Stiles-Crawford effect reflects how photoreceptors couple light into the retina depending on where the light enters the pupil. It is very strong for cones because their waveguide geometry makes brightness depend on the entry angle. In scotopic (night) conditions, vision is dominated by rods, and rods have much less directional sensitivity to the entry point. Their light-guiding properties don’t produce a noticeable difference in perceived brightness as light enters from different pupil locations. So, under scotopic conditions, the Stiles-Craw Crawford effect is essentially not present. That’s why the best answer is that there is no noticeable difference.