Yönäkö

Yönäkö, also known as night vision, is the ability to see in low-light conditions. It is a complex physiological process that involves several adaptations in the eye. Humans possess a limited form of night vision, primarily due to the presence of photoreceptor cells called rods in the retina. Rods are highly sensitive to light and are responsible for scotopic vision, which operates in dim light and produces monochromatic (black and white) images. In contrast, cones are responsible for photopic vision in bright light and provide color perception.

The effectiveness of human night vision is influenced by factors such as age, vitamin A levels, and exposure to bright light. Prolonged exposure to bright light can temporarily impair night vision by bleaching the photopigments in the rods. Adapting to darkness typically takes about 20 to 30 minutes, during which time the rods become more sensitive.

While human night vision is limited, many animals, such as owls, cats, and certain insects, have significantly superior night vision. These animals often possess a higher density of rods, a reflective layer behind the retina called the tapetum lucidum which bounces light back through the retina, and larger pupils that allow more light to enter the eye.

Technological advancements have also led to the development of artificial night vision devices. These devices use various methods, including image intensification, thermal imaging, and digital enhancement, to allow humans to see in conditions that would otherwise be impossible. Image intensification amplifies existing light, while thermal imaging detects heat signatures. These technologies have applications in military, security, and scientific research.