Dark adaptation means: the eyes adapt to darkness.
The eyes become more sensitive after spending time in the dark.
At first, the sky can feel empty.
After about 20–30 minutes, more faint stars and faint detail appear.
Nothing in the sky changed.
The eyes changed.
Two parts of vision share the work:
Cones
• bright light
• color
• adapt fast (a few minutes)
Rods
• low light
• night vision
• adapt slow (about 20–30 minutes)
Bright white light interrupts this.
A phone screen, headlights,
or a white torch can reset night vision.
Red light is used for a reason.
Rods respond much less to deep red light.
So red light disturbs night vision much less than white light.
Dark adaptation matters most for:
• faint stars
• faint nebulae
• faint galaxy arms and halos
What helps preserve night vision during a session?