iPhone Blue Light

In this guide, we’ll walk you through how to optimize the light coming from your iPhone.

How to Turn on Night Shift

The first thing every iPhone owner should do is enable Night Shift mode!

So if you haven’t done that yet, here’s how…

Go to “Settings” → “Display & Brightness” → “Night Shift” and then turn on “Schedule“.

I recommend scheduling Night Shift to start about two hours before your bedtime, and to turn off before you usually wake up in the morning.

Make sure to set the “Color Temperature” slider all the way to “More Warm”.

screenshot of iphone settings page highlighting display and brightness
screeenshot of display and brightness page highlighting night shift
iphone night shift settings screenshot

Does Night Shift Block Blue Light?

We own a lab-grade spectrometer, so we decided to see what kind of an impact Night Shift has on the light output from an iPhone 12 Mini at about 8 inches from the screen…

Here’s an actual comparison of the light spectrums before and after using Night Shift:

spectral power distribution graph of iphone 12 pro with truetone enabledspectral power distribution graph of iphone 12 pro with night shift enabled

As you can see Night Shift significantly cuts down on blue light and reduces the green a little too!

graph of iphone 12 pro lux before and after night shift
graph of iphone 12 pro circadian light before and after night shift

The total lux dropped from around 37 to 21 which is around a 43% decrease in the “brightness” of the screen.

While the circadian light, which is a weighted algorithmic calculation of the blue and green light capable of suppressing melatonin, dropped by about 70%.

You should definitely have this enabled at night.

However, even with Night Shift mode activated, the iPhone still emits some blue light and quite a bit of green, and for many people, this can still suppress melatonin and promote wakefulness.

This is why you might want to enable the red screen filter!

How to Turn Your iPhone Screen Red

Go to “Settings” → “Accessibility” → “Display & Text Size” and then click on “Color Filters“.

screenshot of iphone settings page highlighting accessibility
screenshot of iphone accessibility page highlighting display and text size
screenshot of iphone accessibility page highlighting color filters

Now set the Intensity and Hue sliders to the max. This will cause your screen to become very red!

screenshot of iphone color filter page highlighting settings
screenshot of iphone with color filter settings at max

You can turn the color filter off after this, we just needed to set the tint so that when we turn it on in the future it will already be red.

Setting the Color Filter Shortcut

Go to “Settings” → “Accessibility” → “Accessibility Shortcut” and then click on “Color Filters“.

screenshot of iphone accessibility page highlighting accessibility shortcut
screenshot of iphone accessibility shortcut page highlighting color filter option

Congratulations! Now you can triple-click your power button to toggle the red light filter on and off as you please.

How Well Does the Color Filter Work?

This is all good and well, but how well does it work?

Here’s a spectral reading of our iPhone with Night shift enabled, before and after enabling the red color filter.

iphone 12 pro night shiftspectral power distribution graph of iphone 12 pro with night shift and red filter enabled

As you can see, all of the blue light has been obliterated, and just about all of the green is gone too!

Here’s a graph of an iPhone’s spectral radiation comparing all three modes:

spectral power distribution of iphone 12 pro before and after night shift and red filter

This is pretty great! Everyone should have this enabled on their iPhone in my opinion.

This brings me to my next suggestion…

Bonus: Automating the iPhone Red Filter!

While you can certainly use the triple-click to turn on and off your red light filter whenever you want, I personally prefer to automate it!

This is useful of course because who wants to remember to enable this every night at a specific time? Feh!

Open the “Shortcuts” app then the “Automation” tab. From here click on “Create Personal Automation“.

Now you have to choose the trigger for your red light filter, either “Time of Day” or “Sleep“.

screenshot of the automation tab in the shortcuts app
screenshot of iphone automation triggers screen highlighting time of day and sleep

Time of Day will give you the option to select Sunset or a specific time as the filter trigger.

If you’ve set up sleep mode on your iPhone (which I recommend), Sleep will give you the option to trigger the filter when your wind-down begins. This is the one that I use.

screenshot of time of day trigger
screenshot of sleep trigger

Once you’ve selected one of these, tap on “Add Action“, search “Color filter” and select “Set Color Filter“. It will be set to “On” by default, then hit “Next” on the top right.

iphone screenshot highlighting add action button in automation app
iphone screenshot of automation action search
iphone screenshot of automation verification page

Finally, uncheck “Ask Before Running“, and hit “Done“.

iphone screenshot highlighting ask before running button in automation app

Now repeat these steps to create an automation that turns off your red light filter before you usually wake up in the morning!

And bam! You now have a fully circadian-optimized iPhone. I’m so proud of you.

The bonus of making your screen red before you go to bed is that this makes doom-scrolling Instagram and YouTube far less enjoyable which will keep you off of those dopamine soul-sucking apps before bed, which is a good thing!

Another way to block this disruptive screen light would be to use either daytime or evening blue-blocking glasses.

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  1. I Derek the article was great and really clear, it helped a lot 🙂 thanks

    I am wondering how do you get the spectral from the screen is there any way to get it using a application or you use a external device to measure it? I would like to see if it is possible to measure by myself.

    Thanks in advance

    1. Glad you found it helpful! So measuring the actual spectrum from a screen would be quite expensive… the closest you’ll get on a budget is perhaps an Opple meter which should be able to show you lux and color temperature, among a few other things.