Why You Crash at 7 PM Every Evening | LightTherapy.no

By Dominic Lamb – LightTherapy.no

You've made it through the day. Work done, dinner sorted, kids (maybe) headed towards bed. You had a mental list of things you actually wanted to do tonight - that project, that workout, even just sitting and reading without falling asleep in the chair. And then it happens. 7 PM arrives and something just... collapses. Heavy limbs. Foggy head. The sofa pulls at you like gravity doubled. You pick up your phone instead of doing any of the things you meant to do, vaguely guilty about it, too depleted to stop.

The evening energy crash is not a willpower problem, and it is not a sign you're getting old. For most people living in Norway, it is a biological response to an evening routine that is systematically fighting against your circadian system - primarily through light. Switching to red and amber lighting after 6 PM and using blue light blocking glasses (blålysbriller) after 7 PM allows melatonin to rise naturally, cortisol to fall on schedule, and your mitochondria to manage energy properly rather than burning through reserves responding to false daytime signals.

What is actually happening to your energy at 7 PM

Your daily energy isn't a simple tank that empties as the day goes on. It's managed by your circadian system - the network of molecular clocks in your cells that regulate when to burn energy, when to restore it, and when to begin winding down. The master clock, your suprachiasmatic nucleus (SCN), coordinates this across your entire body, including your liver, your muscles, your fat cells and your brain. And the primary input it uses to keep everything synchronised is light.

Specifically: the timing, intensity and spectrum of light your eyes receive throughout the day. Light in the morning - particularly the full-spectrum quality of early sunlight - sets your circadian phase. It tells your SCN it's daytime, triggers a healthy cortisol rise, sharpens alertness and sets the metabolic tone for the whole day. Light in the evening, by contrast, is supposed to be dimming and warming. That shift is the signal that tells your body to begin the transition toward rest.

Does that sound familiar as a description of your evenings? I'd guess not.

What most of us actually do after 6 PM is flood our homes with bright, blue-rich LED lighting running at 4000-6000 Kelvin - the same spectral quality as midday sun. We aim screens at our faces at close range. We sit under overhead lights that measure 100-300 lux and contain almost no red or near-infrared wavelengths. As Professor Glen Jeffery at UCL has documented in his research on spectral quality and mitochondrial function, modern LED lighting is heavily blue-dominant and essentially red-starved compared to both natural sunlight and the incandescent lighting most of us grew up under. Your cells don't experience that as a neutral background. They experience it as a biological signal - and the signal says: it's still the middle of the day.

The melatonin and cortisol part nobody explains clearly

Blue light around 480nm stimulates melanopsin-containing cells in your retina that connect directly to your SCN. Research published in the Journal of Biological Rhythms confirms that even relatively dim light - around 50-100 lux - is sufficient to suppress melatonin if it contains those short wavelengths. Your living room at 7 PM is running at 100-300 lux of LED light. That is more than enough to tell your pineal gland: hold the melatonin, it's not night yet.

Melatonin suppression alone would be enough to explain the crash. But it compounds. Evening light exposure also keeps cortisol elevated when it should be falling. Cortisol should be at its lowest in the late evening - that's part of what allows a genuine wind-down. When light keeps it up, your nervous system stays activated. You feel what most people describe as simultaneously exhausted and wired. You're too tired to do anything useful and too activated to sleep properly. So you scroll, which adds more blue light, which extends the problem.

Then around 9 or 10 PM, your body eventually forces the issue and you hit the floor. Poor sleep follows. You wake up tired. The next day's energy reserves start lower than they should. By 7 PM the following evening, the whole pattern repeats.

You're not imagining the cumulative drain. Think about it honestly - do you need to sleep in at weekends to recover from the week? That deficit is real, and the evening light environment is a significant driver of it.

The mitochondrial side of the story

There's a layer underneath the melatonin and cortisol story that I find even more interesting, and it connects directly to why red light therapy has such a pronounced effect on people's energy levels when they use it correctly.

Your mitochondria - the primary sites of cellular energy production - are directly responsive to light wavelengths. Cytochrome c oxidase, the terminal enzyme in the mitochondrial electron transport chain, has absorption peaks in the red (around 630-660nm) and near-infrared (around 810-850nm) ranges. When red and near-infrared light reaches those chromophores, it drives electron transport, increases ATP output and reduces what's called the proton backpressure that limits energy production efficiency. A 2024 study by Professor Jeffery's group published in the Journal of Biophotonics found that just 15 minutes of 670nm red light exposure reduced blood glucose spiking by 27.7% over two hours by increasing mitochondrial glucose demand - which is a remarkable effect from a relatively short light exposure. You can read the paper here: https://pubmed.ncbi.nlm.nih.gov/38010845/

Modern LED lighting provides essentially none of those wavelengths. You are spending your evenings in a light environment that activates the biological pathways that should be quiet (via blue light) and fails to provide the wavelengths that support mitochondrial function (red and near-infrared). The result is an energy system that is being asked to keep running on signals that are actively working against it.

I use a red light panel in my morning routine partly for this reason - not to replace an active evening practice, but because I want my mitochondria functioning well before the day starts, not fighting through a deficit created by the night before. The evening changes described below are what stop the deficit accumulating in the first place.

What I actually changed - and what happened

About five years ago I started experimenting with my evening lighting. Not because I expected it to transform my evenings - I was trying to improve my sleep, which had been getting worse. I'd also been training clients in the evenings for years and noticed that even on nights when I'd worked hard physically, I'd hit that same 7 PM wall on my days off. Which told me it wasn't just exertion.

The protocol I tested was simple. After 6 PM, overhead LEDs off. Red and amber lamps on instead. Around 7 PM, amber-lens blue blocking glasses on and kept on until sleep. Screens after 8 PM only if unavoidable, brightness reduced, dark mode where possible.

First week: it was strange. Everything looked orange. My wife thought I'd lost it. I committed to two weeks regardless.

Second week: the crash didn't disappear, but it changed character. Instead of a collapse, it became a gentle downshift. I still felt tired - I was supposed to feel tired by 9 PM - but I had what felt like usable energy between 7 and 9 that I hadn't had before. I noticed I was falling asleep naturally around 10 rather than lying wired in the dark until 11.

Third week: the evening crash essentially stopped. Not replaced by artificial energy - I wasn't buzzing around. Just functional. Present. Capable of actually choosing what I did with my evenings rather than defaulting to the sofa out of depletion.

My wife started doing it within the month. My daughter (I say nothing to her about it, she'd find a way to be sceptical on principle) consistently falls asleep faster on evenings when we've had the red and amber lamps on in the living room. She doesn't know that. I do. I keep a quiet mental record.

I caught myself on my phone at 11 PM last Tuesday without my glasses on. Literally sell the things. Still get pulled in - the algorithm is genuinely designed to be hard to escape, and I'm not immune to it. But I noticed within about ten minutes, put the glasses back on, and went to bed. Progress, not perfection.

Why this matters differently for us in Norway

In summer, this is manageable. Daylight runs late and your circadian system gets reasonably clear signals even through a messy evening. But for a good chunk of the year - roughly October through April - the Norwegian light environment means you've had almost no meaningful daylight exposure during working hours, and you come home to an interior flooded with the wrong kind of artificial light at exactly the time your biology most needs the opposite.

The combination of insufficient morning light (which should set the circadian phase early and ensure a natural evening wind-down) and excessive evening blue light is what turns the 7 PM wall from an occasional bad night into a structural feature of your winter. It's worth reading what I wrote about artificial lighting choices for Norwegian homes if you want to understand the spectral differences between your current bulbs and what would actually support your biology - it changes how you think about the lamps you buy.

The evening light environment also directly affects the family. If you have children and they're getting the same blue-rich LED exposure in the evenings, their melatonin timing shifts too. Later, harder sleep onset, more night waking, more difficult mornings. I've written about this in more detail over at the nighttime light and family mood guide - it's worth a read if you've got kids who fight sleep.

The minimum viable change - what to actually do

You don't have to rebuild your entire home lighting setup in a week. The hierarchy of impact looks like this, in order of how much difference each step tends to make.

Start by switching off overhead lights after 6 PM and replacing them with table lamps running warm bulbs at 2700K or lower, positioned below eye level. The lux reduction alone has a meaningful effect. Then add blue light blocking glasses at 7 PM - amber lens for general evening use, red lens if you want maximum blocking in the hour before bed. Wear them consistently rather than occasionally; the circadian benefit comes from regular nightly signalling, not one-off protection.

If you want to go further: screens off by 8 or 9 PM when possible. For those who genuinely have to work in the evenings, do it under warm lamp light with glasses on. I work on the business in the evenings regularly. I do it with amber glasses on under a red lamp on my desk. The work happens. The sleep doesn't suffer. That's the relevant test.

One thing worth knowing about the glasses: I test the lenses I stock with a spectrometer before I'll put them in the shop. The difference between a lens that genuinely blocks the relevant wavelengths and one that just looks amber to the human eye is significant. I market ours as blocking around 97% of blue light because that's what my test results show. Not 100% - because that's not what the spectrometer reads and I'd rather be accurate than sound impressive. If you want to see the actual readings, I've put them up on Instagram (@home_light_therapy).

The biphasic dose response matters here too, in the sense that doing too much - wearing red-blocking glasses all evening from 5 PM, living in total darkness by 7 - isn't the goal. You want a gentle, gradual shift that mirrors what natural sunset provides. That's what your circadian system is calibrated for. Work with the biology rather than trying to override it in the other direction. (This principle applies to red light therapy too - more isn't always better. I've written about why here, and it's worth understanding before you build any light protocol.)

What the science says about adenosine and the wired-tired feeling

There's one more mechanism worth explaining because it answers a question I get regularly: why does the evening crash sometimes feel like exhaustion and alertness at the same time?

Adenosine is a molecule that builds up in your brain throughout the day - it's often described as the biological measure of sleep pressure, the longer you're awake the more you accumulate. In a well-functioning system, adenosine levels rising in the evening combine with falling cortisol and rising melatonin to produce a clean transition toward sleep. You feel genuinely tired, not buzzed, and sleep comes relatively easily.

Bright evening light disrupts this by keeping cortisol elevated even as adenosine is high. The result is that your brain is simultaneously carrying high sleep pressure and high alertness signals. This is the wired-tired state. Coffee or another screen in that state can temporarily override the adenosine - which is why a lot of people reach for both - but it does so by borrowing against tomorrow's energy and pushing sleep onset later. A 2019 study in Current Biology demonstrated that evening light exposure significantly delayed the circadian phase even at relatively low intensities, with knock-on effects on sleep architecture and next-day alertness. Read the study here: https://pubmed.ncbi.nlm.nih.gov/31761715/

The fix isn't to suppress the adenosine signal. It's to let the cortisol fall the way it's supposed to, which means removing the light stimulus that's keeping it elevated. When cortisol drops on schedule, adenosine and melatonin do their job, and the transition to sleep feels natural rather than something you're fighting your way into.

For a deeper look at the sleep science specifically, including what the most recent research says about light and sleep architecture, the post on new science on light and sleep for Norwegian winter goes into more detail than I can here.

A realistic expectation of how long this takes

One week of consistent implementation and most people notice something. The crash becomes less severe. Sleep onset feels easier. Mornings don't feel quite as brutal.

Two to three weeks and the pattern typically shifts more meaningfully. Usable evening energy instead of a collapse. Natural tiredness arriving at a sensible hour rather than either crashing early or staying wired too late.

I've never had someone implement this consistently for three weeks and report no change at all. That doesn't mean it works identically for everyone - if there are other things going on, other drivers of poor sleep or depleted energy, this alone won't fix all of it. But it will make the other things easier to address because you're no longer running the circadian system actively against yourself every single evening.

If you want to test it properly: track your evening energy on a 1-10 scale for a week under your current routine. Then implement the changes for two weeks with the same tracking. Compare. The data will tell you more than I can.

Your evenings don't have to be a daily write-off. The biology is not complicated. Give it the signals it's expecting - dim, warm light as the sun goes down, blue wavelengths removed from your eyes in the hours before sleep - and it will start doing what it's designed to do. Which includes leaving you with actual energy for the hours after 7 PM.

If you want to talk through what changes make sense for your specific setup - lighting, glasses, any red light use - the FAQ page covers a lot of the common questions, or message me directly. That's genuinely what I'm here for.

The blue light blocking glasses are the highest-impact lowest-cost starting point. The circadian lighting range covers lamps and bulbs for the room environment. Start with one, see what happens, build from there.