Definition
Rods are one of the two types of light-sensitive cells (photoreceptors) in the retina of the eye. They are concentrated around the outer edges of the retina rather than at the center, and they are responsible for peripheral vision and for seeing in low-light or night conditions. Rods do not detect color and do not produce sharp detail, but they are far more sensitive to dim light than the other photoreceptor type (cones).
Plain English
Rods are the cells in the eye that let you see in the dark. They sit around the edge of the back of the eye, see only in shades of grey, and are not good at fine detail — but they pick up faint light much better than the cells used for daytime vision.
Context Anchor
Seen in night flying discussions about how the eye adapts to darkness and why pilots use off-center viewing at night.
Derivation
The cell is called a 'rod' simply because of its shape — it is long and rod-shaped under a microscope. Knowing this helps the pilot remember that rods and cones are named after what they look like, not what they do.
Why Pilots Care
Rods provide the main means of seeing outside the cockpit at night, but they need 30 minutes or more to fully adapt and lose effectiveness if exposed to bright light.
Grounding Statement
In very low light, your rods do much of the seeing, so night vision depends on using them correctly.
Intuition Check
Rods does not mean control rods or metal rods here. In this context, rods are tiny cells in the eye that help you see in dim light.
Example Sentence 1
Because rods are not located at the center of the retina, pilots use off-center scanning to see faint traffic lights at night.
Example Sentence 2
After sitting in the darkened cockpit for thirty minutes, the rods had adapted enough for the pilot to read the dimly lit instruments without a flashlight.