Dark adaptation is the eye's adjustment to low light — by chemical regeneration of visual pigments in cones and rods.
Two phases
| Phase | Receptor | Full adaptation time |
|---|---|---|
| First phase | Cones | ~ 7 minutes |
| Second phase | Rods | ~ 30 minutes |
Sensitivity improves moderately in the first ~7 minutes (cones adapt); full rod adaptation continues more slowly to maximum at ~30 minutes.
What destroys adaptation
- Bright white light even for a few seconds destroys rod adaptation entirely.
- Flash, overly bright cockpit lighting, ramp floodlights.
- Daytime sun exposure before a planned night flight — wear sunglasses.
Preserving adaptation
| Measure | Effect |
|---|---|
| Red cockpit lighting | Rods barely respond to red — adaptation preserved. Drawback: red chart markings disappear |
| Heavily dimmed white | Compromise — some rod loss, chart colours remain visible |
| Eye patch on one eye during outdoor work / refuelling | Preserves adaptation in the covered eye for after entry |
Practical application
Before a night flight:
- ~30 minutes before flight, move to a darkened room.
- On the ramp, use red or dimmed white flashlight.
- No smartphone at full brightness (blue light destroys adaptation).
- Set cockpit lighting as dim as possible before eyes hit the panel.
Don't forget
- Altitude degrades night vision further: from 5 000 ft night sensitivity is measurably reduced (see Hypoxia §2.2).
- Smoking reduces night vision via CO-Hb — even hours before the flight.