Twilight: Blue light filter

Are you struggling to fall asleep at night? Do your children become overly active when using tablets before bedtime? If you're using smartphones or tablets in the evening, or if you're sensitive to light during migraines, Twilight could be the perfect solution for you.

Recent studies indicate that exposure to blue light before bedtime can disrupt your natural circadian rhythm, making it difficult to fall asleep. This disruption is caused by a photoreceptor in your eyes known as Melanopsin, which is sensitive to blue light in the 460-480nm range. This sensitivity can inhibit the production of Melatonin, a crucial hormone for maintaining healthy sleep-wake cycles. Research has shown that reading on a tablet or smartphone for a couple of hours before bed can delay sleep by about an hour.

Twilight is designed to adjust your device's screen to the time of day, filtering out blue light after sunset and applying a soothing red filter to protect your eyes. The intensity of the filter smoothly adjusts based on your local sunset and sunrise times, ensuring a seamless transition. Twilight is also compatible with Wear OS devices, allowing you to maintain consistent filtering across your gadgets.

For those interested in the science behind it, here are some resources on circadian rhythm and the role of melatonin:

• Melatonin
• Melanopsin
• Circadian Rhythms
• Circadian Rhythm Disorder

Twilight offers several benefits:

1. Bed Reading: Twilight provides a more comfortable reading experience at night, capable of dimming the screen beyond the standard backlight controls.
2. AMOLED Screens: Extensive testing on AMOLED screens over five years shows no signs of depletion or over-burning. With proper configuration, Twilight reduces light emission while ensuring even light distribution, which may even extend your screen's lifespan.

To function optimally, Twilight requires certain permissions:

• Location: To determine your local sunset and sunrise times.
• Running Apps: To disable Twilight in selected applications.
• Write Settings: To adjust the backlight.
• Network: To connect with smart lighting systems like Philips HUE to filter blue light from your household lighting.

For comprehensive filtering, including notifications and the lock screen, Twilight may request access to the Accessibility Service. This service is used solely to enhance screen filtering and does not collect any personal information. Learn more about this at Twilight's Accessibility Service.

For Wear OS users, Twilight syncs your watch's screen with your phone's filter settings, controllable via a "Wear OS Tile."

If you're interested in automation, Twilight can be integrated with services like Tasker. For more details, visit Twilight Automation.

The effectiveness of Twilight is supported by various scientific studies, including:

• "Amplitude Reduction and Phase Shifts of Melatonin, Cortisol and Other Circadian Rhythms after a Gradual Advance of Sleep and Light Exposure in Humans" by Derk-Jan Dijk & Co, 2012.
• "Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans" by Joshua J. Gooley & Co, 2011.
• "Effect of Light on Human Circadian Physiology" by Jeanne F. Duffy & Charles A. Czeisler, 2009.
• "Efficacy of a single sequence of intermittent bright light pulses for delaying circadian phase in humans" by Claude Gronfier & Co, 2009.
• "Intrinsic period and light intensity determine the phase relationship between melatonin and sleep in humans" by Kenneth P. Wright & Co, 2009.
• "The Impact of Sleep Timing and Bright Light Exposure on Attentional Impairment during Night Work" by Nayantara Santhi & Co, 2008.
• "Short-Wavelength Light Sensitivity of Circadian, Pupillary, and Visual Awareness in Humans Lacking an Outer Retina" by Farhan H. Zaidi & Co, 2007.

For more detailed documentation on Twilight, visit Twilight Documentation.