Light mode vs Dark mode

Spoiler alert — If you are reading this blog in dark mode, maybe it’s time to rethink your decision!

I assume everyone who is reading this, knows the difference between dark mode (left, i.e white text on black background)and light mode (right, i.e black text on white background). Image: My Medium Profile :)

So, before we try to understand which one is better, let’s visit some flashback

1. ~Dark mode → ~Light mode → Dark mode

Our screen technology approximately started with dark mode. It goes like this: The earliest methods to display something on screen is to use cathode ray tubes which can brighten/illuminate one or few pixels at a time, so it’s natural to have a dark background and illuminate the few pixels to form the required shape.

With research advancements in screen coloring, we were able to experience approximately light mode (or basically the color mode) where we can vary the contrast between the background and foreground (thus different colors on screen). And this light mode actually went well for a couple of decades till major companies like Apple, Google, Microsoft released “Dark mode” (I believe it’s around 2018!)

Left: Early days Monochrome screen (~dark mode). Right: Early days multicolor screen (~light mode). Pic credits: IBM, Apple Macintosh

2. Comeback of Dark mode → Why?

But why did the companies released a dark mode and why is there so much craze for it. Almost every company/app promotes dark mode for 2 reasons:

1. Better battery life:

Well, if we think, it kinda makes sense! Imagine each pixel (basically the smallest block on your screen) is a bulb. If you use light mode, most of your screen is white/bright and thus has to use lots of bulbs to light up the screen. On the other hand, if you use dark mode, most of your screen is dark, thus it won’t use a lot of bulbs. So, roughly speaking:

Light mode → More bulbs to light up (emits more light) → More battery consumption (faster drain)

Dark mode → Less bulbs to light up (emits less light) → Less battery consumption (slower drain)

Caveat: This is true only if your device has OLED display. Otherwise, dark mode consumes almost same energy as light mode. So, Dark mode might be better for environment if everyone has OLED display!!

Several people have done experiments with different setups and the general consensus is that dark-mode drains slower compared to light-mode (Image source: Wccftech)

2. Reduced eye strain:

Hmmm…companies (and many people) point out that it reduces eye strain. But is that true? If so, how does it make sense?

Let’s take a sidewalk and learn something about photography as it’s very similar!

Focus

Camera lenses has something called Aperture (f-number) which basically controls the amount of light that can enter the camera. A higher f-number (f/32) (constricted) means the lens sends only a little amount of light and a lower f-number (f/1.4) (dilated) means the lens sends huge amount of light.

We usually use lower f-numbers when the surroundings are dark (to allow more light) or to get that beautiful Bokeh effect i.e shallow depth-of-field (DOF). The same way, when the environment is too bright or if we need wide depth-of-field (DOF), we increase the f-number, to make sure most of the light is blocked.

Different aperture sizes for a typical lens. Lower f-numbers blur the background i.e not everything in sharp focus and higher f-number has everything in sharp focus. Roughly, Bright environments → Higher f-number and Dim environments → Lower f-number (Pic credits: PhotographyHero)

The same applies to our eyes as well (infact the cameras are designed by the principle of eyes to an extent!) So, roughly speaking:

Dark Mode → Appx Dark environment, low light situation → Eyes/Pupils dilate (lower f-number) → Has lower DOF i.e not everything is in focus → Eyes strain while reading long texts

Light mode → Appx Bright environment → Eyes constrict (higher f-number) → Has higher DOF i.e everything is in focus → Eyes won’t strain that much while reading long texts.

So, prefer reading in light mode!

Note: I didn’t take the surroundings into account (bright vs dim environments) but the general consensus is to use that mode which feels comfortable/less strainy to your eyes.

Astigmatism, light scatter and Halo effect

Physics101 → Black absorbs light and white reflects light!

So, in dark mode, when the text is white, the light that’s hitting the text gets reflected/scattered and that affects the capability to focus on nearby text. Whereas in light mode, the text absorbs light and so won’t cause any such scattering.

It might not be super clear from the image, but basically light mode is comfortable to the eye muscles. Image source: https://uxmovement.com/content/when-to-use-white-text-on-a-dark-background/

An image explaning the Halo effect on text. It might be a bit exaggerated for people with normal vision, but it’s how it looks for people with Astigmatism. (Pic credits: https://www.youtube.com/watch?v=bCaFRN3aaP8)

This problem is more severe for people suffering with Astigmatism (an eye disorder). They’ll have hard time reading in dark-mode text, as the light scatters away and it becomes difficult for them to focus on the text!

Contrast

We can read something because of the simple rule — “background is different from foreground”. That’s roughly known as contrast i.e what’s the difference between the text and background screen. Simply,

Different contrasts of the same text with various foreground/background colors (Pic credits: Colorado State University)

Very High contrast → Easier to read, but causes eye strain, Very Low contrast → Difficult to read, Medium contrast → Easier to read and reduces eye strain

Eg: Twitter’s background isn’t fully black! It’s dark blue background with white text

Don’t use “very high contrast” screens. It’s like turning on a bright light in a dark room! Our retinas can’t take the sudden change in incoming light (Pic credits: https://uxmovement.com/content/why-you-should-never-use-pure-black-for-text-or-backgrounds/)

Light mode ~ Skeumorphism

Designing the technology to look as close to as it’s real world counterpart is termed as skeumorphism. This basically forms a minimum barrier for humans in terms of getting adjusted to the product.

Apple calculator evolving and incorporating skeumorphism in their design (Pic credits: AppleInsider)

If we think like this, from centuries, we read paperbacks/books/scriptures with dark text placed on light background, so it’s natural to assume that our eyes have evolved and has a preferential bias towards this!

Final words:

My purpose is not to demonize dark mode but to understand more about this area. With the invention of light bulbs, computers and smartphones, we are at an uncharted territory whereas our ancestors roamed in daylight and slept at night. Whatever the claims one says regarding the effect of technology on our eyes (or brain in particular), it’s not backed up by centuries of research (not even a lifetime of research tbh)!

An alarming concern for which no researcher has concrete answer on aftermath. Image source: https://www.pewresearch.org/internet/2020/07/28/childrens-engagement-with-digital-devices-screen-time/

So, just take any advice with a pinch of salt and my only suggestion is to “be conscious” of what you are doing.

Advices:

While I am definitely not a doctor or any medical practitioner, here are some advices that are scientifically sound (do experiment and check what works best for you):

1. Take continuous breaks when working with screens. Close your eyelids, rotate the eyeballs and just relax it. It also has muscle connections that needs break!
2. Experiment and try to use light mode if you are planning to read for long time. Programmers → Even coding is a sort of reading, so if you got convinced, it’s time to sacrifice dark mode from your favourite IDEs :(
3. If you read books→ Paperbacks > Kindle screen > Light mode with eye comfort filter on > Dark mode
4. If you spend more time in front of screen (focusing on text etc;), try to use light mode. If you are watching videos or just eyeballing/scrolling, dark mode works decently well.
5. Don’t use your devices in low light environments for a long time!!! Always have some bed light when reading/watching screen.