Twilight: Blue light filter

Petr Nálevka (Urbandroid)

About this app

Are you having trouble falling asleep? Are your kids hyperactive when playing with the tablet before bed time?
Are you using your smart phone or tablet in the late evening? Are you sensitive to light during migraine?
Twilight may be a solution for you!

Recent research suggests that exposure to blue light before sleep may distort your natural (circadian) rhythm and cause inability to fall asleep.

The cause is the photoreceptor in your eyes, called Melanopsin. This receptor is sensitive to a narrow band of blue light in the 460-480nm range which may suppress Melatonin production - a hormone responsible for your healthy sleep-wake cycles.

In experimental scientific studies it has been shown an average person reading on a tablet or smart phone for a couple of hours before bed time may find their sleep delayed by about an hour. See references below..

The Twilight app makes your device screen adapt to the time of the day. It filters the flux of blue light emitted by your phone or tablet after sunset and protects your eyes with a soft and pleasant red filter. The filter intensity is smoothly adjusted to the sun cycle based on your local sunset and sunrise times.

You can also use Twilight on your Wear OS device.

Documentation
http://twilight.urbandroid.org/doc/

Get more from Twilight
1) Bed reading: Twilight is more pleasant on the eyes for night reading. Especially as it is able to lower the screen backlight far below the ability of the backligt controls on your screen

2) AMOLED screens: We have tested Twilight on an AMOLED screen for 5 years without any sign of depletion or over-burning. If properly configured Twilight causes less light emission (by enabling dimming) with more equal light distribution (dark areas of the screen such as the status bar get tinted). This may in fact increase your AMOLED screen life time.

Basics on circadian rhythm and the role of melatonin
http://en.wikipedia.org/wiki/Melatonin
http://en.wikipedia.org/wiki/Melanopsin
http://en.wikipedia.org/wiki/Circadian_rhythms
http://en.wikipedia.org/wiki/Circadian_rhythm_disorder

Permissions
- location - to find out your current sunset/surise times
- running apps - to stop Twilight in selected apps
- write settings - to set back-light
- network - access smartlight (Philips HUE) to shield you household light from blue

Accessibility Service

In order to filter also your notifications and lock screen the app may ask for enabling Twilight Accessibility Service. The app uses this service only to better filter your screen and does not collect any personal information. Please read more about this at https://twilight.urbandroid.org/is-twilights-accessibility-service-a-thread-to-my-privacy/

Wear OS

Twilight also syncs your Wear OS screen with your phone's filter settings. You can control filtering from a "Wear OS Tile".

Automation (Tasker or other)
https://sites.google.com/site/twilight4android/automation

Related scientific research

Amplitude Reduction and Phase Shifts of Melatonin, Cortisol and Other Circadian Rhythms after a Gradual Advance of Sleep and Light Exposure in Humans Derk-Jan Dijk, & Co 2012

Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans Joshua J. Gooley, Kyle Chamberlain, Kurt A. Smith & Co, 2011

Effect of Light on Human Circadian Physiology Jeanne F. Duffy, Charles A. Czeisler 2009

Efficacy of a single sequence of intermittent bright light pulses for delaying circadian phase in humans Claude Gronfier, Kenneth P. Wright, & Co 2009

Intrinsic period and light intensity determine the phase relationship between melatonin and sleep in humans Kenneth P. Wright, Claude Gronfier & Co 2009

The Impact of Sleep Timing and Bright Light Exposure on Attentional Impairment during Night Work Nayantara Santhi & Co 2008

Short-Wavelength Light Sensitivity of Circadian, Pupillary, and Visual Awareness in Humans Lacking an Outer Retina Farhan H. Zaidi & Co, 2007

Ratings and reviews

I adore this app. As someone with visual snow syndrome, I've tried all kinds of screen filters and dimmers, and this one is my favorite by far. One of the things that aggravated me most about other ones is having to go into the app and manually turn everything off to take a screenshot without the color being heavily altered, but this one has a built in pause and screenshot function accessible from the notifications bar!

Edit:OOF. What the actual #@&?. For the past day(2/25/25), each time I hit the icon to turn Twilight on or off from the drop-down menu, the brightness adjusts DRAMTICALLY, automatically And it does this randomly now too..?? It's blinding. WHY. Had it for more than a decade.. }}} It saves my head from migraines. It doesn't disturb my circadian rhythms at night. It's a life-saver. You can customize the running time, and turn it on or off instantly as needed right from the pulldown menu.

Twilight makes all the difference. Installing and using this app has been so beneficial to my eyes, especially at night while reading in bed. You can set it to bedtime setting and there is absolutely no strain on your eyes. What a sight savior! The free model has been fine for now, but I am going to check into paid version and the differences. Good job developers.!

What’s new

- Targeting Android 15
- Edge to edge support
- Fix for scrolling to last option and large DPI settings
- New libraries