Can Dark Mode Save Battery Life and Human Civilzation?
A zillion years ago I was shown
blackle.com, it's google, but with a black background.
Blackle was a black page with a google search bar. It swapped the bright white background of
So, we all changed our homepage to
blackle and saved the planet. Actually, the fad of using
blackle ended as fast as it started. We found out that
blackle had no impact on our screens' energy use and forgot all about it.
Low Impact Manifesto — article 9 #
The other day someone sent me a link to the Organic Basics - Low Impact Website. It's an e-commerce site designed to minimize environmental harm.
The code is open source, and comes with a manifesto describing 10 things a low impact site should do.
Number nine says a low impact site "Limits the amount of light emitted by the screen." I remembered
blackle and how it had turned to be a disappointment. But the people who built this site did their research, I should do mine. So I got to googling (blackling?)
CRT vs LCD vs OLED #
It was around 2007-08 when i first saw
blackle.com and most screens were
liquid crystal displays.
LCD screens are illuminated with a backlight. The liquid crystals change color, but can't emit light themselves. The backlight is on no matter what the screen is displaying.
No matter how bright a pixel is the energy consumption doesn't change. So a site like
blackle has no impact on power consumption.
blackle first launched in 2002 the majority of screens were
CRTs do use less electricity when the screen is black.2
CRTs also use a lot more electricity than
blackle really did make sense.
LCD is still the most popular but will soon be overtaken by
OLED screens are made up of pixels that emit light independently of each other. What's more, the power consumption directly correlates with the brightness of each pixel. So the less bright a pixel, the less electricity is used.
Using a site like
blackle, or setting your phone to
dark mode really does save power. But how much?
How much energy does dark mode save? #
Mobile Enerlytics is a company that measures the energy use of phones. They did some experiments and concluded that
dark mode saves a lot of battery life. Between
44.7% on a device at full brightness and
The big differences in percentage of energy-use depends on the activity of the phone. A
cpu heavy task, like watching a video, uses a lot of energy, so comparatively less energy is used by the display. For simpler tasks, like reading an article,
dark mode results in much longer battery life.
dark mode does significantly improve battery life. But how much energy is being saved? And how does that translate to
Back of envelope calculation #
I've no idea how to find an accurate answer to this. But rough calculation should put things in perspective. We'll use the iPhone X specs4 as a guide.
iPhone X uses a
20 watt charger and takes
~1 hour to charge. If you charge it fully once per day, that's
20 watt hours a day,
7.2 kilowatt hours a year.
In the USA
CO2 is emitted per
KWh.5 Let's assume we're saving only
dark mode. So
iPhone Xs on
dark mode for a year would save about
CO2. The same emissions as 31 cars.6
1 Million iPhone X's on dark mode saves ≈ 31 Cars emissions
There are more than
200 million cars in the USA. So, I'll let you decide if
dark mode is worth thinking about as solution to the climate crisis.
Personally, I think small gains like this add up. The climate crisis is a complex issue. Every source of
C02 can be broken down to smaller and smaller parts. Eventually issues like this need to be solved. Luckily for us,
Dark mode will happen on its own.
Dark mode isn't about saving the planet. It's about usability and to a lesser extent battery life.
dark mode gets more popular, consumers will expect it from apps and websites. The environmental gains will come for free.
Computer World - lcds gain ground against crt monitors ↩︎
Scientific America – Black Is Better than White for Energy-Efficient Screens ↩︎
Mobile Enerlytics – Dark Mode ↩︎
iPhone X Specifications ↩︎
U.S. Energy Information Administration — How much carbon dioxide is produced per kilowatthour of U.S. electricity generation? ↩︎
EPA – Greenhouse Gas Emissions from a Typical Passenger Vehicle ↩︎
- 5 Jan 2021
- 5 Jan 2021