Get a Good Night’s Sleep by Filtering Your Phone’s Blue Light

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How often do you get a good night’s sleep? If the answer is anything less than “Always”, then you might want to consider the impact your gadgets are having on your nightly slumber.

While it’s common for many of us to unwind in the evening reading eBooks, watching Netflix or catching up on Facebook on our phones or tablets, experts are united in their belief that this is not healthy.

man reading smartphone

As a 2012 report (PDF) by the American Medical Association’s Council on Science and Public Health concluded: “…exposure to excessive light at night, including extended use of various electronic media, can disrupt sleep or exacerbate sleep disorders”.

So what exactly is the problem, and what can we do about it?

The Problem with Blue Light

Studies have repeatedly warned that using gadgets in the evening affects both the quantity and quality of our sleep.

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The cause is exposure to light at night time. Or, more specifically, it’s exposure to short wavelength blue light — the kind given off by our phones and tablets and pretty much any gadget with an illuminated display.

blue light

Sunlight also contains blue light, and it is vital during the day. It’s what helps to keep us awake and alert, and it’s an integral part of how sleep cycles work.

But exposure to blue light at night is a bad thing, as it effectively tricks your brain into thinking that it’s still daytime. It suppresses the secretion of melatonin, a hormone that is produced at night and prepares the body for sleep.

Its impact is so great, in fact, that another study even suggested that having a blue LED shining from a car dashboard would be an effective way of preventing drivers from falling asleep at the wheel.

Incidentally, melatonin suppression isn’t just linked to poor sleep. Some reports have linked it to illnesses like cancer and diabetes too.

blue light filter

So, what do you do, short of turning your phone off hours before you go to bed?

Head into the Play Store, and you’ll find numerous apps that provide the solution: they filter out the blue light entirely.

The Solution

Most of the blue light filtering apps work in a similar way. They do nothing during daylight hours, but after sunset place a red overlay on the screen to change its color temperature.


This gives everything a red hue, which takes a little getting used to. But it also cancels out the negative effects of the blue light, and massively decreases glare. Even if you’re skeptical about it improving your sleep, you will immediately notice a reduction in eye strain when using your phone in a dimly lit room.

The apps aren’t perfect. The use of a red overlay reduces contrast, and it turns blacks into a dark shade of red.

They also trigger a security feature in Android where certain buttons become inaccessible when overlays are in place. You’ll most likely notice it if you attempt to install an app from somewhere other than the Play Store. You have to pause or close the filtering app to be able to press the Install button.


Twilight (free and pro) is arguably the best of the standard blue light filtering apps. It progressively reduces the color temperature of the display (making it redder) and dims the screen until your chosen levels of color and brightness are reached.


This gradual change means that you barely even notice it happening. At first whites are no more than slightly off-white, but by the time you’re in bed browsing Reddit, the effect will be in full force.

By using your phone’s light sensor, Twilight is able to constantly adjust its settings automatically, ensuring they always suit your ambient lighting conditions. Once you get past the initial setup, you’ll never need to touch the app again.

The Root Option: CF.lumen

Twilight is a great choice for most users, but if your Android phone is rooted, you can choose a more powerful option.

CF.lumen is also a blue light filter (among other things — it has options for colorblind users too), but as a root app, it’s able to work at the display level. Instead of applying a red overlay to cancel out the blue light, it uses a custom driver to directly control which colors the display physically shows.

As well as being potentially more efficient, it also produces a much higher quality output. Blacks remain black, and there’s no loss of contrast. As a result, the screen is easier to read and the overall effect is less jarring.


CF.lumen uses your location to determine the times of sunrise and sunset where you are. By default, it applies the Sundown Color Filter at sunset (above, center). This is a red filter, the strength of which you can adjust to taste. Between 1am and 5am it switches to the hardcore Sleep Color Filter (above, right), which displays luminance from the red channel only.

CF.lumen can be downloaded from the Play Store in a fully-functional free version, and you can upgrade for $3.99 to remove a few nag screens.

Inevitably, as a root app, the install/uninstall process is a little more involved. When you launch the app for the first time you are prompted to install the custom drivers, which requires a reboot. And it’s important to remember to uninstall them again via the app should you ever choose to uninstall the app itself.

If you don’t have root access, the app will work in “rootless” mode, where it reverts to using an overlay like Twilight.

Reduce the Effect of Blue Light Without Filtering It

The reddening effect of blue light filtering apps is a little strange, but in my experience it’s fairly easy to get used to.

But some people just don’t like it. If this is you, then there are still things you can do to minimise the effects of blue light.

night mode

The key is to reduce the amount you are exposed to. So, using a phone instead of a tablet is better due to the smaller screen. Reduce the brightness as much as you can, and if you’re using apps that have a “night mode”, use that.

Most eBook readers have white-on-black or sepia options that are far better than having a white background. The team behind an eBook reader with a built-in blue light filter, Oyster, is now part of the Google Play Books team, so hopefully Google’s eReader may adopt something similar in future.

Sub-Zero Brightness With Lux

To make these adjustments automatically, try Lux (free and paid). This app enables you to override your phone’s settings and choose your preferred brightness levels for every ambient lighting condition.


This includes a sub-zero setting that makes the screen dimmer than the standard brightness slider allows. Not only does this completely eliminate glare in low light, but it’s a great way of improving your battery life too.

Lux also offers countless power user features, which may be overkill for some. They include the app’s own blue light filter, integration with CF.lumen, and root support that enables it to work with custom kernels.

What Do You Use?

Apps like Twilight or CF.lumen enable you to freely use your Android phone without it stopping you from getting to sleep, or leave you feeling groggy in the morning.


If a laptop is more your thing, then f.lux does a similar thing for Mac, Windows and Linux. There’s also an iOS version, although it requires a jailbroken iPhone or iPad.

None of us want to give up on our gadgets in the evening, and by taking care of their adverse side effects we won’t have to.

Do you use your phone at night? Have you ever tried a blue light filtering app? Let us know your thoughts in the comments.

Image credits: phone in darkness by Mila Supinskaya via Shutterstock, Man reading smartphone via

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