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Why do nocturnal animals often have more rods than cones?

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Compound eye — Senses Vespid wasps (Vespidae), similar to other insects, have compound eyes that consist of thousands of tiny optical units known as ommatidia, which contain light-sensitive photoreceptor cells.

Nocturnal animals often possess a higher density of rod cells compared to cone cells because rods are significantly more sensitive to low levels of light.12

While cones function best in bright light and are responsible for color vision, they are relatively insensitive to weak light stimuli. In contrast, rods are specialized for scotopic (dim-light) conditions; they contain the pigment rhodopsin, which allows them to detect light at very low intensities, even responding to single photons. By having a higher proportion of rods, nocturnal animals maximize their ability to perceive movement, shape, and brightness in environments where light is scarce, such as during twilight or at night.13245

Many nocturnal vertebrates further enhance this sensitivity with a tapetum lucidum, a reflective layer behind the retina that gives light a second chance to be absorbed by the rod cells. This evolutionary adaptation prioritizes light sensitivity over the ability to perceive color or fine detail, which are secondary to survival in dark habitats.621