The Right Light at the Right Time

If you spend any time in the health, wellness or biohacking world, you have probably come across the argument that sunglasses block the sunlight your body needs to set its circadian rhythm, and that wearing them all day is quietly working against you.

There is something real in that, and it is worth taking seriously. The biohacking crowd have hold of a genuine piece of science. It has just been carried a little further than the evidence goes.

Morning light does matter, more than most of us realise, and so does keeping ultraviolet radiation out of your eyes at noon in an Australian summer. The two are not in conflict. It comes down to timing.

Why morning light matters

Light in the first few hours after you wake is what sets your circadian clock, and it remains the strongest timing cue your body has. It shapes how alert you feel during the day and how easily you fall asleep that night, so reaching for sunglasses at that hour does dull a signal you would rather keep.

Behind the rods and cones that let you see, the retina holds a third kind of light-sensitive cell containing a pigment called melanopsin. These cells contribute almost nothing to vision. Their job is simply to tell the brain what time of day it is, and they respond to bright light, which turns out to mean brighter than most of us imagine. A well-lit room sits at roughly 300 to 500 lux, while an overcast morning outdoors runs into the thousands and full daylight into the tens of thousands. Standing at a window is not quite the same thing either, since glass filters out a good deal of what those cells are reading.

Here is what the evidence supports, in rough order of confidence.

Body clock timing. Well established, with a mechanism that is understood and reproducible.
Sleep. Strong. Morning light brings forward the evening release of melatonin, which is part of why early light tends to make for earlier and easier sleep.
Mood. Promising, though not settled. The largest study so far followed 86,772 adults wearing light sensors on their wrists, and found that more daytime light was associated with lower rates of depression, PTSD and self-harm, independent of night-time light. It was cross-sectional, so it shows an association rather than cause and effect. Encouraging, but not something to lean on too heavily.
Children's eyesight. Time spent outdoors in daylight is one of the more consistent protective factors against short-sightedness developing in children. That one has less to do with sunglasses and more to do with getting kids outside.

In practice it is fairly simple. Try to get outside within an hour or two of waking, for ten or twenty minutes on a clear morning and a little longer if it is grey. There is no need to look at the sun, and you shouldn't. Just being out in it, without sunglasses, while the light is still low is enough.

So are sunglasses harmful?

Not in the way the argument suggests. The version that travels furthest holds that sunglasses stop the body producing melanin and therefore contribute to skin cancer. Melanin, though, is made in the skin itself, by cells called melanocytes responding to ultraviolet light landing on the skin, rather than being switched on by a hormone triggered through the eyes.

The argument also tends to skip past what ultraviolet light does to eyes over time, which is where the picture gets more complicated.

What UV does to your eyes

The ophthalmic evidence here is fairly consistent. In the short term there is photokeratitis, which is essentially sunburn of the cornea and usually settles within a day or two. Over longer periods the evidence points to pterygium, the fleshy growth across the white of the eye that is common enough among Australian surfers and outdoor workers to have picked up the name surfer's eye, and which occasionally needs surgery. Cortical cataract sits on the same list, along with squamous cell cancers on the surface of the eye, and basal and squamous cell carcinomas on the eyelids, where the skin is thin and sunscreen rarely reaches.

A couple of things often attributed to UV are less certain. The evidence linking it to ocular melanoma is limited, and the evidence around macular degeneration is not strong enough to call either way. It seemed worth saying so rather than lengthening the list. Cancer Council Australia's summary of the eye research is a good place to start if you want to read further.

When should you put them on?

When the UV index reaches 3. That number is not arbitrary. The World Health Organization and ICNIRP set it as the point at which protection becomes necessary, noting that below a UV index of 3 the risk of short and long-term damage is limited even for very fair skin, and recommending sunglasses specifically once you are above it.

The index tracks ultraviolet radiation rather than heat or brightness, which is why a cool, overcast day can still sit above 3, and why squinting is not a reliable guide. In a Sydney summer the index tends to climb past 3 early in the morning and stay there for most of the day, while in midwinter it may only brush 3 around noon. The free SunSmart app and the live ARPANSA feed will both tell you where it is at any given moment, which is easier than guessing.

That gives you a rhythm you can actually keep. Walk early without them, put them on once the index crosses 3, and leave them on.

Where polarised lenses earn their place

Anywhere light is bouncing off a flat surface. Water, wet roads, snow, sand and the bonnet of a car all qualify. Light reflected off a horizontal surface becomes horizontally polarised, and a polarising filter is built to cancel exactly that, which is why a polarised lens lets you see into the water rather than at it.

The reflection figures are worth knowing. According to the World Health Organization, snow can return as much as 80 per cent of UV back at you, sea foam around 25 per cent and dry sand about 15 per cent, while open water and grass sit under 10 per cent. UV also climbs with altitude, by roughly 10 per cent for every 1,000 metres, and ARPANSA notes that levels at Australian ski fields can run up to 30 per cent higher than at sea level.

That explains something most people have felt without quite being able to name it. A day on the boat or on the snow is harder on your eyes than the forecast number suggests, because you are taking UV twice, once from above and once from below. It is also where the headache and the tired, gritty eyes at the end of a long, bright day tend to come from.

Polarisation and UV protection are not the same thing

This is the distinction worth carrying into a shop with you. Polarisation deals with glare, while UV protection comes from the lens material and its coatings, and they are separate properties. An inexpensive lens can be dark and polarised and still let UV through, which is worse than wearing nothing at all, because the tint opens your pupils up behind it.

Australia at least sets a floor here. Since July 2019, anything sold as sunglasses has had to meet AS/NZS 1067.1:2016, and ARPANSA notes that sunglasses tested to the Australian requirements offer more UV protection than those tested to international standards. The categories run from 0 and 1, which are fashion spectacles and not much use in real sun, through 2 and 3 for general wear, up to category 4, which is made for high glare on the water, the snow and in the desert, and is not legal to drive in.

Every Pacifico frame is fitted with polarised Carl Zeiss Vision lenses, so both jobs are handled by the same lens. The frames are made from plant-based Japanese acetate, and they are designed and tested in Bondi, which is a fair place to find out whether a pair of sunglasses can hold up to a summer.

A quick guide

Situation	UV index	What to do
First hour or two after waking	Usually under 3	Outside without sunglasses, for ten to twenty minutes
Once the index crosses 3	3 and above	Sunglasses on. Category 2 or 3 for everyday wear
Midday in summer	8 to 14	Sunglasses, a broad-brimmed hat, and shade where you can find it
On or near water	Any	Polarised makes the biggest difference here
Snow	Any	Polarised and close fitting, category 3 or 4
Driving	Any	Polarised cuts road and bonnet glare. Avoid category 4
Overcast	Worth checking	Cloud does not stop UV, so let the index decide

Common questions

Is it bad to wear sunglasses every day?
Not if you are getting some daylight in your eyes early on. The issue is rarely the sunglasses themselves. It is spending the whole day indoors and then wearing them for the twenty minutes you do get outside.

Do I need sunglasses on a cloudy day?
Check the UV index rather than the sky. Cloud scatters visible light more than it blocks ultraviolet, so an overcast day can still sit comfortably above 3.

Are polarised lenses better than non-polarised?
For glare, yes, and noticeably so near water, snow and wet roads. For UV protection, polarisation makes no difference at all. That comes from the lens itself.

Can I get morning light through a window?
Only partly. Glass cuts a lot of the intensity, and intensity is really the point, so ten minutes outside will do more than an hour at the window.

What about sunglasses at sunset?
Take them off. The index is back under 3 by then, and the light is doing useful work at the other end of the day.

The short version

Get outside early without them. Put them on once the UV index reaches 3. Wear polarised anywhere light is bouncing off water, snow or road. The biohackers are right that light is a signal your body reads closely. Where it goes wrong is in the conclusion that the answer is to stop protecting your eyes.

This article is general information rather than medical advice. If you have concerns about your eyes or your sleep, it is worth seeing an optometrist or your GP.