Why You Need a Flashlight

At night, a power outage occurs. Time to find a flashlight, you can move into the house with your night vision. How it works? Explanations.

Vertebrates and arthropods are animals with a highly developed vision. The human eye is improved and is comparable to a camera which the retina is the film. At any time of day, day and night, our eye adapts to our environment to ensure the best possible vision.

The lens and cornea deal adjust the image, iris handles brightness. Photons, light particles, penetrate to the retina that will be responsible for replacing the light stimulus into electrical stimulation that will reach the brain via the optic nerve. The brain then reconstructs the image. This stimulus conversion is possible through specialized retinal cells sensitive to super bright light, the photoreceptors. But if they are reactive to light, how it works in the dark?

Why You Need a Flashlight 1

To Each His Specialty

Two types of receptors are present in the retina of the human eye: the rods and cones. Cones allow to discern colors; as to sticks, they give a panchromatic vision, that is to say in black and white.

In the darkness, the rods are most useful for our so called scotopic vision, ie in low light. They have a high sensitivity to light; low intensity, the rods become active through their pigment, rhodopsin.

Why You Need a Flashlight 2

A Pigment Cascade

A light, rhodopsin is inactive form. It is split into two elements, opsin and retinene (an aldehyde of vitamin A). Immediately after transfer in darkness, the active stock of rhodopsin to be reconstituted in order to achieve the maximum sensitivity for scotopic vision is optimal. This takes some time, which explains the adaptation period of our eye that we could see properly in the dark. This requires not mean thirty minutes.

The synthesis of active rhodopsin is done in two ways:

The way slower from vitamin A requires oxidation which requires a significant metabolic expense.

When rhodopsin reached its sensitivity threshold is around 500 nanometers, then it excites the stick that sends the info nerve to the brain.

The sticks are mostly on the periphery of the retina. This explains why we do not distinguish an object face in the dark, but very well against its outline is seen.

Why You Need a Flashlight 3

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