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# Your Bedroom Isn't As Dark As You Think, And Your Heart Rate Knows It
- URL: https://lights-out.ghost.io/bedroom-light-heart-rate-insulin/
- Published: 2026-09-01T00:30:47.000Z
- Updated: 2026-09-01T00:30:46.000Z
- Description: A single night under light dim enough to call "dark" still raised heart rate and next-morning insulin resistance in a Northwestern trial. Here's what's actually leaking into your room.
- Author: Claire Ashton
- Tags: Free Fixes, Bedroom Enviorment, Hack Stack

| You already did the blackout curtains, so you assume the light problem is solved. Stand in your room tonight with every switch off and count what's still glowing: charger, smoke detector, router, the gap where the curtains don't quite meet the wall. Manufacturers put a bright standby LED on almost everything you own, on purpose, so you always know it's working. Here's what a 2022 Northwestern trial found when researchers put that question to the test. A single night under light dim enough to call comfortable, about the brightness of a hallway, raised heart rate through the night and produced measurable insulin resistance by morning. Nobody in that study noticed anything unusual before lights-out. It's not your fault. Your nervous system reacts to light your eyes barely register. A room doesn't have to look bright to keep your body half-awake, it just has to glow. WHY DIM STILL COUNTS Light reaches receptors in your eye that don't care whether you're conscious enough to call the room dark. Those receptors feed straight into your sympathetic nervous system, the one that runs your fight-or-flight response, and they keep firing at levels most people would describe as barely-there. Your brain never gets the full stand-down signal it needs. It just keeps one hand on the wheel all night. THE EVIDENCE Phyllis Zee and Daniela Grimaldi at Northwestern University's Feinberg School of Medicine, publishing in *PNAS* in 2022, put healthy adults through **100 lux** for one night, about the brightness of a dim hallway, and 3 lux for another. That level of light raised heart rate through sympathetic activation and produced measurable insulin resistance the next morning. TONIGHT'S WALKTHROUGH THE FREE FIX (2 MINUTES) Turn off every light and stand in your room for two minutes before bed tonight. You're looking for anything still glowing: charger, smoke detector, the gap in the curtains, since most people find four or five sources they'd stopped noticing months ago. THE $2 FIX Cover every small indicator light you found with a piece of electrical tape. A router light or charger light doesn't need to stay visible to keep working. Black tape or a small sticker blocks it completely, and it takes less time than finding the remote. THE $8 UPGRADE Add blackout curtain liner clips to seal the gaps at the top and sides. The glow doing the damage rarely comes through the fabric. It sneaks around the edges, where the fabric meets the wall. Clips or velcro strips seal that gap without replacing curtains you already paid for. THE HALLWAY SWITCH If you need a light on for safety, make it red or amber, not white. Warm, low wavelengths disturb those same receptors far less than white or blue light does, so a ten dollar amber night-light in the hallway does the job without undoing everything above. And one more thing... Blocking the light only gets you partway there. The rest is giving your body what it needs to wind down once the room actually goes dark. **Zinc and B6** show up together in a handful of formulas for exactly that reason, supporting the enzyme pathway your body uses to convert everyday nutrients into the compounds that regulate sleep. It's a quieter combination than most of what gets marketed at night, mostly because tape and curtain clips don't come with a subscription. Deal with the light first. Everything else works better once the room is actually dark. QUICK QUESTION Have you ever done a lights-off scan of your bedroom? [YES](mailto:Claire%20Ashton%20%3Cmeloucou@gmail.com%3E?subject=Yes%20-%20I%27ve%20Done%20This&body=Yes%2C%20I%20found%20more%20than%20I%20expected.) [NO](mailto:Claire%20Ashton%20%3Cmeloucou@gmail.com%3E?subject=No%20-%20Never%20Checked&body=No%2C%20never%20checked.) Sleep well,Claire Ashton |
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