Small study suggests dark mode doesn’t save much power for very human reasons

If you know how OLED displays work, you know about one of their greatest strengths: Individual pixels can be shut off, offering deeper blacks and power savings. Dark modes, now available on most operating systems, aim to save power by making most backgrounds very dark or black, while also gratifying those who just prefer the look. But what about on the older but still dominant screen technology, LCDs? The BBC is out with a small, interesting study comparing the light and dark modes of one of its website pages on an older laptop. Faced with a dark mode version, most people turned up the brightness a notable amount, sometimes drawing more power than on light mode. It's not a surprise that dark modes don't do anything to reduce LCD power draw. However, the study—not peer-reviewed but published as part of the International Workshop on Low Carbon Computing—suggests that claims about dark mode's efficiency may be overstated in real-world scenarios, with non-cutting-edge hardware and humans at the controls.

A 2017 MacBook Pro, a power monitor, and the brightness keys

The R&D arm of the British Broadcasting Corporation got to wondering just how useful a dark mode was in lowering broader power consumption. So the team "sat participants in front of the BBC Sounds homepage and asked them to turn up the device brightness until they were comfortable with it," using both the light and dark mode versions of the BBC Sounds website.

Faced with the dark mode version of the site, 80 percent of participants turned the brightness up "significantly higher" than in light mode, the BBC writes in its blog post. In the study, the Beeb posits something broader:

Our findings suggest that the energy efficiency benefits of dark mode are not as straightforward as commonly believed for display energy, and the interplay between content colourscheme and user behaviour must be carefully considered in sustainability guidelines and interventions.

The study used a physical power monitor (a Tektronix PA1000) and two laptops, one for testing—a 2017 MacBook Pro with a 13.3-inch LCD display—and another for monitoring. The LCD laptop seems like a curious choice, given that dark mode's savings are largely tied to OLED pixel technology. The BBC study suggests that, "given that most devices still use LCDs, where power consumption may not be reduced by displaying darker colours" (British spelling theirs), broad claims about energy savings may not be appropriately scaled. It's a decent point. The BBC study points to a write-up on the blog of consultancy firm Valtech of a Purdue study for evidence of those broad claims. The Purdue study puts the savings of dark mode, when using OLED displays with auto-brightness enabled, at between 3–9 percent, and the savings at 100 percent brightness at up to 47 percent. But how many devices will see that benefit? Research firm Omdia suggested in mid-2024 that OLEDs held 53 percent of the smartphone display market. In 2023, the same firm saw OLEDs as being 14 percent of the combined tablet and laptop market by 2028. So while smaller screens are ready to save some power with black pixels, our larger, more energy-hungry LCD displays are, by and large, not saving much from dark mode and may be just the opposite.

Dark MacBook, dark room, light savings

The BBC's experiment put 10 people 50 centimeters (1.6 feet) from the BBC Sounds homepage and asked them to alter the brightness until they were comfortable looking at it. Every participant did this adjusting in four variations: dark mode and light mode, and in a dimly lit and brightly lit room. Measuring across 16 brightness levels, the BBC found little difference in power draw between dark and light modes—but, again, this is an LCD screen, so that was expected. The lighting in the room also had very little impact on the brightness level and power draw. Using dark mode, however, caused the mean brightness level set by the participants to increase from a range of 9.6–10.7 in light mode to 12.5–12.7 in dark mode, with standard deviations around 2.1 for dark mode and 3.2 for light mode. The highest and lowest brightness settings chosen by participants also crept up in dark modes. The BBC study is just 10 participants, and, as the broadcaster itself notes, calls out for the same study to be done with OLED displays, which have higher contrast ratios and may be easier to read in dark mode at lesser brightness. There are also accessibility and page design considerations not brought into this exercise. But one website, on one MacBook, hooked up to a power monitor can at least suggest that organic eyes and real computers complicate the conversations around dark mode power savings.