You've optimized your diet. You go to bed at a reasonable hour. You still feel foggy by mid-afternoon and wired but exhausted by 10pm. If this sounds familiar, your body may be responding rationally to something you haven't considered: the light around you.
The Signal You're Not Getting
Your circadian system depends on consistent, high-intensity light exposure during the day to regulate cortisol, the hormone associated with alertness and energy. Researchers estimate that most adults in industrialized environments receive a fraction of the light exposure their circadian system is calibrated to expect — often measured in a small percentage of what's considered a full daytime dose.
The result, according to circadian researchers, is a system that's underexposed during the day and overexposed at night — indoor lighting in the evening, at levels well above what's associated with a properly timed melatonin release.
The Symptoms That Don't Add Up
If you've ruled out the obvious explanations and still feel off, these are patterns researchers have associated with a mismatched light environment:
- Afternoon energy crashes despite adequate sleep duration
- Difficulty waking up, even after seven or eight hours in bed
- Wired-but-tired evenings, where you're too alert to fall asleep but too drained to function
- Mood dips during darker months or in spaces with little natural light
None of these are diagnostic on their own — many things can cause fatigue or low mood, and this isn't a substitute for ruling out other causes with a healthcare provider. But researchers studying circadian health have consistently linked inconsistent light exposure to disruptions in these exact patterns.
Your Body Isn't Broken — It's Responding
This is the reframe worth sitting with: what feels like a personal failure — can't focus, can't sleep, can't get going in the morning — may actually be a rational biological response to an environment your body was never designed for. Indoor, artificial, always-on light is a relatively new experiment in human history.
What to Notice
You don't need a lab test to start paying attention. Notice how you feel on days you get real outdoor light in the morning versus days you don't. Notice what happens to your evening energy when you dim the lights two hours before bed versus when you don't.
Your body has been giving you this information the whole time. Most of us just haven't been taught to read it.