I tracked my cortisol at home to see if blue light glasses really work - here are my test results

2 hours ago 6

Me, wearing my Gunnar Dume Gold blue light blocking glasses.

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ZDNET's key takeaways

I used cortisol tests to see if blue light glasses reduced stress.
I compared the glasses with meditation and avoiding screens.
The glasses helped, but so did deep breathing and avoiding screens.

I've been curious about whether screens disturb my sleep. After all, I'm someone who spends a fair amount of time in front of them most days. As far as I'm aware, I sleep pretty well, but who knows? I could be sleeping much better.

Science suggests screen use, especially in the evening, may trigger spikes in cortisol, the stress hormone, as a result of the blue light emitted by screens and the constant influx of overstimulating information. There are also links between blue light from screens and suppressed melatonin, a hormone that regulates sleep. There's also data to suggest limiting exposure to blue light may be beneficial.

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But I've steered clear of this topic because I didn't have any real method of measuring cortisol -- until now. Cortisol tests are something you can buy (you can get finger-prick tests that you send off to a lab, as well as super convenient saliva tests you can do at home). Since I was in a curious mood, I decided to see what, if any, difference blue light-blocking glasses might make.

The tests I used were the ones where you do a series of finger-prick tests throughout the day (don't worry, I won't be showing any needles or blood or anything), send the blood samples off to a lab, and wait a few days for the results.

A baseline

Before we go any further, let's cover some science about cortisol.

Naturally, this hormone spikes in the morning as part of the normal awakening response to get us out of bed, after which it is supposed to decline slowly throughout the day, tapering off in the evening as we wind down and prepare for sleep. Cortisol levels rise temporarily in response to stressors, like work or emergencies, and prolonged elevation of cortisol is linked to a host of health issues.

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First, I needed a baseline. This was a normal day where I woke up in the morning, got on with things, and then blasted myself with screens in the evening -- the screen in question mostly being my iPhone 17 Pro Max. Judging by the results, screens do indeed affect my cortisol levels. However, some of this was due to something silly I'd done. I'll get back to this later.

Lots of evening screens, no glasses, resulted in a big evening spike.

In the above chart, the blue area corresponds to what is considered the normal range for cortisol throughout the day.

I also noticed my cortisol levels were really high in the morning, but after speaking to a specialist, we concluded this is likely due to the large amount of natural light flooding into my bedroom in the morning (I do love morning light), or that it's elevated from -- drumroll please -- my evening screen use.

Testing blue light glasses

The next day, I did the same routine, but that evening I wore my Gunnar Dume Gold blue-light-blocking glasses. These are some quality glasses. The frames are solid, the lenses perfect, and they are designed to block 65% of blue light at 450nm.

The Gunnar Dume Amber glasses are really nice, like a high-end pair of sunglasses.

And, surprise-surprise, they did seem to lower my evening cortisol levels.

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Lots of evening screens, but wearing my blue light blocking glasses helped to reduce my cortisol.

Next: No evening screens

This was getting interesting.

Next, as a bit of a control, I had an evening where I avoided screens altogether.

I walked, read a book (a real, dead-tree book), walked some more, stuck my AirPods in my ears, fixed a wobbly leg on a table that had been bugging me for weeks, and tidied up my workbench. I was surprised by how much I got done in the absence of being stuck in front of a screen, but it felt somewhat stressful, so I thought my cortisol would be spiked.

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But, just as the science suggests, giving the unending doomscroll a miss for an evening lowered my cortisol levels to what the folks in white coats consider normal levels. Nice.

No evening screens dramatically lowered my evening cortisol levels.

Using a 'TÜV low blue light-certified' screen

I have to admit I was having fun (was this having fun naturally lowering my cortisol?). The next night, I changed screens. Instead of my iPhone, I used an Android handset I had lying around (the Blackview BL9000 Pro) that featured a TÜV low blue light-certified display. The results were pretty good, with my cortisol levels much lower than when I used my iPhone.

Screen time using a TÜV certified low blue light display did a good job of reducing cortisol levels.

Trying Night Shift mode on iPhone

But this is when I remembered something: the iPhone does have a blue light reduction mode that kicks in during the evening called Night Shift. This feature shifts the display colors to the warmer end of the spectrum at sundown. However, because it changes the color of the display -- and I sometimes do photo and video editing on my iPhone -- I'd turned it off a long time ago.

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So, I re-enabled it and repeated the test. It works. Cortisol was down despite my brain being filled with knowledge and information that seemed so important at the time, yet I forgot about it all in minutes.

Evening screen time with the iPhone Night Shift mode enabled showed promising results.

Final meditation test

As a final test, I decided to see if I could lower my cortisol levels by doing something free and easily accessible to us all: breathing exercises. Studies show deep breathing activates the parasympathetic nervous system, which in turn can lower cortisol.

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So, I turned off Night Shift on my iPhone, blasted my face with screens for yet another evening, but before doing the cortisol test, I sat down quietly for 20 minutes and practiced box breathing.

And it worked. In fact, short of avoiding screens altogether, it was the best result I'd seen.

My conclusion… of sorts

OK, before I conclude, remember, I'm not a doctor or a scientist, and I don't play one on TV or the internet. All my conclusions are based on my own limited experiences. So, how did I sleep during this simple experiment?

Oddly enough, despite the significant differences in evening cortisol levels, I didn't feel like my sleep was any better or worse. I did what I normally do. I went to bed, closed my eyes, and woke up the next day.

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The only time my Apple Watch, which I use nightly to track my sleep score, noticed any notable changes was after the evening I completely avoided screens. Even then, I didn't feel my sleep was any different. Maybe I just sleep well naturally, or perhaps it takes more than a day for me to notice any real changes. If anything, I felt avoiding screens was slightly stressful.

I didn't mind spending some time down-regulating before bed with some deep breathing. If nothing else, it feels good -- and it's free.

One change I've made is reactivating the Night Shift feature on my iPhone. (You can check yours by going to Settings > Display and Brightness > Night Shift.) Yes, I have to remember to turn it off if I'm doing anything that involves tweaking the colors of a photo or video -- otherwise, I'll get unpredictable results -- but, most of the time, I don't even notice it's on.

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Another thing I noticed is my eyes felt better and fresher when I wore blue-light-blocking glasses. It was like taking a break and putting cucumber slices on my eyes for a minute or two. They're especially helpful when I'm working on my laptop in the evening.

Normally, I only wear glasses for driving, so it took some getting used to wearing them around the house, but they did make my eyes feel less strained and more refreshed, so the payoff is worth the effort.

I liked the wraparound sides on the Gunnar glasses, something I've not seen on other cheaper blue light blocking glasses. According to the sales literature, this is meant to prevent dry eyes, and I think that it works.

Now, if you'll excuse me, I'm off to do some box breathing.

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