What type of light is primarily used when evaluating visual acuity in scotopic conditions?

When evaluating visual acuity in scotopic conditions, dim light is primarily used. Scotopic vision refers to the ability to see in low-light conditions, where the rod photoreceptors in the retina are predominantly active. These rods are highly sensitive to light but do not perceive color, which is why vision in these conditions is generally less detailed and less colorful compared to photopic vision, where cone photoreceptors are active in brighter lighting.

Using dim light mimics natural scotopic conditions, allowing for an accurate assessment of how well a person can see when visibility is limited. Such an environment helps determine the functionality of the rod cells and overall visual performance under conditions where most people would typically struggle to see clearly.

In contrast, using bright artificial light, direct sunlight, or a flashlight would not accurately represent scotopic conditions. Bright light can overwhelm the rod cells and shift vision into a photopic state, potentially skewing the results of visual acuity tests meant to gauge sensitivity and performance in low-light settings.