Why can't people see colors clearly in the dark?

In the dark, bright colors appear gray and are difficult to distinguish due to the action of two types of photoreceptors in the eye.

Identifying colors can be challenging in the dark. Even with little light, distinct colors can look extremely similar. Distinguishing colors in the dark is more difficult than during the day because human color perception changes according to how we see under different lighting conditions.

The human eye contains two types of photoreceptors, or neurons that detect light, which are rods and cones. Each type of photoreceptor contains light-absorbing molecules called labile pigments, which undergo chemical changes when exposed to light. This triggers a chain of effects at the photoreceptor, prompting it to transmit signals to the brain.

Rod cells are responsible for vision in the dark, called night vision or dark-adapted vision. They consist of multiple layers of unstable pigment, according to Sara Patterson, a neuroscientist at the University of Rochester in New York. This special type of cell collects light well even when it is dark due to its ability to absorb photons. Photons are particles of electromagnetic radiation that form visible light. Rod cells can be activated by exposure to relatively few photons.

On the other hand, cone cells are responsible for diurnal vision, or light-adapted vision. Most people have three types of cone cells, each sensitive to a different range of visible light wavelengths, corresponding to different colors. Slight changes in light-absorbing molecules in cone cells cause them to specialize in detecting red, green or blue light.

However, individual cone cells cannot distinguish between colors, according to AP Sampath, a neuroscientist at the University of California, Los Angeles (UCLA). When a molecule inside a cone cell absorbs a photon, it simply activates the cone cell. At another point, no information about color or light intensity is processed. Color vision arises when the brain combines responses from all three types of cone cells in the eye. Tiny biological circuits convert that reaction into the colors we see.

Cone cells dominate vision in bright conditions because rod cells are quickly saturated or overwhelmed by photons and the brain does not pay attention to rod cell activity. That’s why we can easily see colors during the day. But when it gets darker or the room lights are turned off, rod cells begin to dominate because they are more sensitive to light than cone cells. Rod cells dominate night vision while cone cells are only weakly active. However, unlike cone cells, there is only one type of rod cells. Color vision comes from comparing the responses of three types of cone cells. This does not happen with rod-dominated vision. Therefore, in the dark, we cannot clearly distinguish colors.

By Editor

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