In the dark, vibrant colors seem to fade to gray and become difficult to distinguish due to the activity of two types of photoreceptors in the eye.
Identifying colors can become a challenge for humans in low light conditions. Even with minimal light, different colors can appear very similar. Distinguishing colors in the dark is harder than during the day because human color perception changes based on how we see under different lighting conditions.
It is challenging for humans to see colors clearly at night. (Photo: Dmitri T).
The human eye contains two types of photoreceptors, or light-detecting nerve cells, which are rods and cones. Each type of photoreceptor contains light-absorbing molecules known as unstable pigments, which undergo chemical changes upon exposure to light. This activates a chain reaction in the photoreceptors, prompting them to send signals to the brain.
Rods are responsible for vision in low light, known as night vision or scotopic vision. They consist of multiple layers of unstable pigments, according to Sara Patterson, a neuroscientist at the University of Rochester, New York. This special type of cell effectively gathers light even in darkness due to its ability to absorb photons. Photons are particles of electromagnetic radiation that make up visible light. Rods can be activated with relatively few photons.
On the other hand, cones are responsible for daylight vision, or photopic vision. Most people have three types of cones, each sensitive to different ranges of visible light wavelengths, corresponding to different colors. Minor changes in the light-absorbing molecules in cones make them particularly adept at detecting red, green, or blue light.
However, individual cones cannot distinguish colors, according to A. P. Sampath, a neuroscientist at the University of California, Los Angeles (UCLA). When a molecule inside a cone absorbs a photon, it only activates that cone. At this point, no information about color or light intensity is processed. Color vision arises when the brain combines the responses from all three types of cones in the eye. Tiny biological circuits transform that response into the colors we perceive.
Cones dominate vision in well-lit conditions because rods quickly become saturated or overwhelmed by photons, and the brain does not pay attention to rod activity. This is why we can easily see colors during the day. However, as it gets darker or when lights are turned off, rods begin to dominate since they are more sensitive to light than cones. Rods take over night vision while cones operate weakly. Unlike cones, rods only consist of one type. Color vision comes from comparing the responses of the three types of cones. This does not occur in vision governed by rods. Therefore, in the dark, we cannot clearly distinguish colors.
