Screens, blue light, and getting sleepy

Hello, I’m Tyler Donahue, a program manager on the Windows shell team.

You probably find yourself looking at some sort of screen at night - setting an alarm on your phone, watching a video, reading an eBook, or replying to that one last email. Sure, you can dim your screen at night, but what about the actual color of light you’re looking at during the evening—does that matter? There is some basis to think so. Research indicates that blue wavelength light in the visible spectrum suppresses the production of melatonin, a hormone that regulates your sleep-wake cycle.

Bright sunlight keeps us awake and alert throughout the day. After sunset, melatonin production ramps up because it’s dark out. Unfortunately, artificial sources of blue wavelength light, like screens and light bulbs, continue to suppress melatonin when we should be getting sleepy instead.

Visible light range in nanometers

Research on the effects of blue light on healthy sleep patterns, requests from customers through the Feedback Hub, and the general popularity of apps that reduce blue light led to the development of night light. Night light changes the amount of blue light emitted from your PC’s screen and can be scheduled to turn on every evening.

Building Night light

A photo of the Windows Shell team at Microsoft

From top left, Tyler (Program Manager), Simon (Program Manager), Michael (Software Engineer), Jeremy (Quality Software Engineer), Chris (Quality Software Engineer), David (Software Engineer), Tyler (Software Engineer Intern), Denny (Software Engineer), Stephanie (Quality Software Engineer), Sarah (Quality Software Engineer)

And not pictured Matt and Dylan (Content Publishing writers)

We got to work! I asked Simon, “Can the graphics team build a component that changes the color temperature of the display?” The lower the color temperature, the less blue light. Think of night light like putting sunglasses on (you can actually buy blue light filtering glasses!).

Color temperature scale from candle light to clear blue sky

David coded up a component to change the color temperature and fine-tuned the color tinting. Michael and Denny set to work coding the night light components and settings page. For the most popular configuration of night light, which is when it automatically turns on at sunset, we had to visit Wikipedia many times to determine how to calculate sunset. We ran into some head-scratching bugs that would’ve happened if scientists in McMurdo Station, Antarctica (a United States Antarctic research center on the south tip of Ross Island) used night light. It’s tricky to calculate sunset when some places don’t have sunset every day!

Finally, Matt and Dylan finalized the text in the night light settings page and organized the how-to articles you’ll find online.

Night light first went out to Windows Insiders and received lots of feedback. Sarah and Stephanie (yes, the one and same Steph @ MSFT) took point on customer feedback and gathered feedback coming from social media, forums, and the Feedback Hub. Jeremy, Sarah, and Chris analyzed telemetry about how customers were using night light and the bugs and reliability issues Windows Insiders (early adopters) were hitting. We spent the next couple months fine tuning night light with bug fixes and feedback requests from Windows Insiders like:

- A few cases where night light was disabled when it shouldn’t have been.

- A wider color temperature range: including setting it all the way down to 1200 K.

- A longer transition time: ranging from 2 seconds to 2 minutes.

Getting started with night light

Let me show you how to use the night light feature:

1. Select the Start button, then select Settings > System > Display.

2. Turn on Night light.

Display settings with a Night light toggle switch

Night light will now automatically turn on at sunset and turn off at sunrise. Every day, it will use your current location to calculate sunset and sunrise for you. If you’d like to customize the settings for night light, go to the Night light settings screen by clicking the blue text below the On button.

Screenshot of Night light settings page

Instead of sunset and sunrise, you can set a schedule that automatically turns night light on and off whenever you want. In winter, I’ll be using this setting to change when night light turns on to 9 pm because sunset in Seattle is at 4:17 pm!

1. Select the Start button, then select Settings > System > Display.

2. Select Night light settings.

3. Under Schedule, turn on Schedule night light.

4. Select Set hours.

5. In the Turn on and Turn off boxes, choose the times you want night light to turn on and off.

Even if you set a schedule for night light, you can quickly turn it on or off anytime. Don’t worry, the schedule will resume the next day.

1. Select Action center on the taskbar, then select Night light.

Screenshot of Night light quick action in the Action center

You can also change the color temperature when night light is turned on to a lower (more red/orange) or higher (more blue/white) color temperature. The lower the temperature is, the less blue light your screen will emit.

1. Select the Start button, then select Settings > System > Display.

2. Select Night light settings.

3. Move the Color temperature at night slider to the color you want your screen to be when night light is on.

If night light is currently turned off, you’ll see a preview of what your screen will look like while you’re moving the slider.

Finally, remember that night light is all about controlling the temperature of the light, which is measured in Kelvin. This is different than the luminance (brightness) of your display. Windows can also optimize the brightness of your display by automatically changing the brightness level based on your current lighting conditions. When you use both settings, night light and automatic brightness, you’ll get the best results!

1. Select the Start button, then select Settings > System > Display.

2. Select the Change brightness automatically when lighting changes check box.

<Note>, if you don’t see this setting, your PC may not have a light sensor, which is required for this feature.

Screenshot of Display settings: Brightness and color

What’s next?

Night light is available in the Windows 10 Creators Update (version 1703). Millions of people are already using night light to do great things on Windows—at night!

Please watch our video about how to use night light in Windows 10.


Here are some reference information to learn more about blue light: