Why can't we distinguish colors well in the dark?

-
Identifying colors can be difficult in the dark, and even in low light different colors can look remarkably similar.

But why are colors more difficult to distinguish in the dark than in bright light?

Humans' ability to perceive colors varies because of the way we see them under different lighting conditions. Human eyes contain two types of photoreceptors, or neurons, that detect light: rods and cones.

Each photoreceptor contains light-absorbing molecules, called photopigments, which undergo a chemical change when exposed to light, prompting the photoreceptor to send signals to the brain.

The rods are responsible for enhancing vision in the dark, and Sarah Patterson, a neuroscientist at the University of Rochester in New York, said that they are made of many layers of light pigments.

She explained that the sticks are particularly good at capturing light even in the dark, because "each of those layers represents an opportunity to absorb photons."

Photons are defined as particles of electromagnetic radiation (in this case, visible light), and the sticks can be activated by exposure to a relatively small number of photons.

Cones are responsible for seeing in bright light, or photopic vision. There are 3 types of cone cells in most people, each sensitive to a different set of wavelengths of visible light, which correspond to different colors.

Small changes in the light-absorbing molecules in the different cones lead to what is called specialization in detecting red, green, or blue light.

Individual cone cells cannot distinguish between colors, said AP Sampath, a neuroscientist at the University of California. When a molecule inside a cone cell absorbs a photon, it only activates the cone; At this point, no information about the color or intensity of the light is processed.

Color vision arises when the brain combines responses from the three types of cones in the eye, and small biological circuits convert those responses into the colors we see.

Cones control vision in bright light, because the rods quickly become saturated, or bathed in photons. The brain adjusts the activity of the rods, so colors can be seen easily in bright light.

But as darkness falls, the rods begin to dominate vision, while the cones are only weakly activated.

Unlike cones, rods come in only one type, making it difficult to distinguish between colors well.

However, sticks may still affect color perception under certain conditions. In dim light, the eye operates in an intermediate range with both rods and cones contributing to vision without one type dominating the other.