What do rods in the eye primarily detect?

Rods are photoreceptor cells in the retina of the eye that are highly sensitive to light, allowing them to function well in low-light conditions. Their main role is to detect light intensity and movement rather than color, which is primarily the function of cones, another type of photoreceptor. Rods are responsible for peripheral vision and the ability to see in dim lighting, which includes assessing brightness and depth perception to some extent. This ability to detect changes in light and the presence of motion makes them essential for nighttime vision and for sensing overall environmental contrasts.

In contrast, while other options touch on aspects related to vision, rods are not specialized for color detection or shape, nor do they solely measure brightness without context. Hence, their primary function aligns with detecting light and depth as part of the overall visual experience.