Light, Sleep & Your Health

Junk Light: What It Is, What It Does To You, and How To Fix It

You've probably heard of junk food. Meet its lesser-known cousin: junk light. It's messing with your sleep, your mood, and possibly your waistline. Here's the science — and what you can actually do about it.

IMAGE: Person in dark room illuminated by phone screen Suggested: Split image showing natural daylight vs artificial screen glow at night

The Short Version

Junk light = artificial light at the wrong time. Your phone at midnight. The office fluorescents all day. It won't blind you, but it will mess with your body clock. That matters because poor sleep is linked to weight gain, low mood, and worse. The fix is free: more daylight in the morning, dimmer lights at night, darker bedrooms.

So what actually is "junk light"?

Let's be clear: "junk light" isn't a medical term. You won't find it in a textbook. It's a useful shorthand for something that is real: the light environment most of us live in is wildly different from what our bodies evolved with.

Think about it. For most of human history, the pattern was dead simple:

Day: Blazing sunlight. 10,000+ lux. Full spectrum.
Evening: Firelight. Warm. Almost no blue.
Night: Darkness. Real darkness.

Now think about your actual day:

Morning: Dim indoor lighting (maybe 200 lux if you're lucky)
Evening: Phone screen inches from your face
Night: Standby LEDs, streetlights, that glowing charger

IMAGE: Natural light vs artificial light comparison Suggested: Side-by-side showing bright outdoor scene vs dim office, or sun spectrum vs LED spectrum

We spend 90% of our time indoors under artificial light — then wonder why we can't sleep.

That's junk light: too dim when you need brightness, too bright when you need darkness, and the wrong colour spectrum at the wrong time.

Blue light: villain or scapegoat?

Here's where it gets confusing. Blue light has become the boogeyman. Screen time = blue light = bad. Right?

Not quite. Blue light in the morning is actually good for you — it wakes you up and sets your body clock. The problem isn't blue light itself. It's blue light at 11pm when your brain thinks it's midday.

Light source	Colour temp	The reality
Midday sun	5,500-6,500K	Blue-rich, but that's fine — it's daytime
Old incandescent bulb	2,700K	Warm and low-blue. Like firelight.
Cool white LED	4,000-5,000K	Blue spike at 450nm. Office standard.
Your phone	6,500K default	Daylight-strength blue, 30cm from your eyes

IMAGE: How white LEDs create blue light Suggested: Simple diagram showing blue LED chip + phosphor = white light with blue spike

White LEDs work by combining a blue chip with yellow phosphor. That creates a spike of blue light around 450nm that doesn't exist in natural light. Stare at that at midnight and your brain gets a very clear message: it's noon, stay awake.

Will screens destroy your eyes?

This is the fear everyone has. And the answer is reassuring:

No, your phone won't damage your retinas.

At normal brightness, screens and LEDs aren't known to cause eye disease. The American Academy of Ophthalmology is clear on this.

Yes, intense blue light can damage retinal cells in lab conditions — but those experiments use intensities far beyond any screen you'll ever use. Your phone is not a welding torch.

But digital eye strain is real.

Dry eyes, headaches, blurred vision — these come from how you use screens (staring without blinking, fixed focus), not from the blue light itself.

IMAGE: Person experiencing eye strain at computer Suggested: Someone rubbing tired eyes at desk, or close-up showing dry/strained eyes

What about blue light glasses? A major Cochrane review in 2023 looked at 17 trials and found they made essentially no difference to eye strain or sleep. Save your money.

The real problem: your body clock is confused

Here's where junk light actually bites. It's not about your eyes — it's about your circadian rhythm.

In 2002, scientists found a third type of light-sensitive cell in the eye. These cells don't help you see. They tell your brain what time it is. And they're most sensitive to blue light around 480nm.

When these cells detect bright, blue-rich light, they send one message: "It's daytime. Suppress melatonin. Stay alert."

That's helpful at 8am. At 11pm? Not so much.

IMAGE: The circadian rhythm / body clock Suggested: 24-hour cycle diagram showing melatonin, alertness, and light exposure

Just 25 lux — a dimly lit room — is enough to halve your melatonin production. Regular room lighting at night does more than you think.

What happens when your clock is off

Mess with your light patterns and the effects ripple outward:

Sleep goes sideways

Evening light pushes melatonin later. You can't fall asleep. When you do, it's fragmented. You wake up tired but feel strangely wired at night. Sound familiar?

Your metabolism takes a hit

Large studies using wearable light sensors found that people with brighter nights and darker days had higher mortality rates and more metabolic disease. Night-time light exposure is linked to obesity and type 2 diabetes — even after controlling for diet and exercise.

Mood suffers

Higher artificial light at night correlates with higher depression rates. Even low bedroom light has been linked to more depressive symptoms in older adults. On the flip side, morning bright light is an established treatment for seasonal depression.

IMAGE: The ripple effects of poor sleep Suggested: Tired person at work, or infographic showing sleep > mood > metabolism connections

One late night won't hurt you. It's the pattern over months and years that matters. And that pattern is something you can change.

Who needs to pay attention?

Kids and teenagers — their eyes let more blue light through (clearer lenses, larger pupils), and they're glued to screens late at night. Research links childhood light exposure to obesity later on.

Older adults — sleep already fragments with age, and bedroom light makes it worse. Studies link even low light levels to poorer sleep and mood.

Shift workers — bright light at night, poor daylight during the day. They have higher rates of metabolic problems and some cancers. The WHO classifies long-term night shift work as "probably carcinogenic."

IMAGE: Different groups affected by junk light Suggested: Teenager on phone in bed, shift worker at night, or older person with sleep issues

Everyone else — if you're tired during the day and restless at night, your light environment is worth examining.

How to fix it (mostly free)

Think of it as a light diet. Bright during the day, dark at night. Simple in theory, requires some habit changes in practice.

Morning and daytime

Get outside within an hour of waking. Even 10-15 minutes. Even on a cloudy day. Outdoor light is 10-100x brighter than indoors.
Work near windows. Light at eye level matters more than overhead fixtures.
Take light breaks. Step outside for a few minutes during the day.

IMAGE: Morning light routine Suggested: Person having coffee by window with morning sun, or walking outside in daylight

Evening (2-3 hours before bed)

Dim the lights. Use lamps instead of overheads. Warm bulbs, low wattage.
Turn on night mode on your phone, tablet, computer. Not perfect, but it helps.
Lower screen brightness. Often matters more than colour temperature.
Set a screen cut-off. Ideally 60-90 minutes before bed for anything stimulating.

Bedroom

Make it actually dark. Blackout curtains or blinds. Cover standby LEDs with tape.
Use a sleep mask if you can't control the room.
Phones out — or at minimum, face-down and on silent.

IMAGE: Ideal dark bedroom setup Suggested: Dark, peaceful bedroom with blackout curtains, no visible LEDs

The three things that actually matter

Morning daylight. Dimmer evenings. Dark bedroom. Do those consistently and you've done 90% of the work.

Common questions

Is "junk light" just another wellness fad?

The term is marketing. The science — circadian disruption from artificial light at night — is well-established. The fad is selling expensive gadgets. The fix is mostly free.

Is my phone worse than the sun?

Not even close. The sun is vastly more intense. The difference is timing: you don't hold the sun 30cm from your face at midnight.

Should I buy blue light glasses?

Probably not for daytime use — evidence says they don't help much. Deep amber glasses worn specifically at night are different; they can help if you must use screens late.

Is any light at night okay?

Very dim, warm light is far less disruptive than bright cool light. If you can read comfortably, it's probably too bright for the hour before bed.

Can I undo years of bad habits?

You can't rewind time, but you can stop adding strain. Many people notice better sleep within days of fixing their light environment.

References

American Academy of Ophthalmology, "Should You Be Worried About Blue Light?" (2021) · Singh S. et al., Cochrane Review on blue-light filtering lenses (2023) · Windred D.P. et al., PNAS (2024) · IARC Monographs Vol. 124, Night Shift Work · US EPA indoor time estimates