Why is it easier to see black text on a white background?

Question

I'm wondering why it's easier to see black text on a white background than it is to see white text on a black background. I say that it's harder based on life experience (Hate webpages with black backgrounds!) and not from any actual studies I know of that have been done. Nonetheless, I think most people will agree with me on this one.

My two general theories are:

1. For some reason it strains the eyes (not quite sure why that would be), and

2. We're just really used to it, so our brains have become wired specifically to process black text on white backgrounds

Answer 1

The short answer is that it is not necessarily easier to read black on white. Contrast is more important in lightness and colour, it just so happens that black and white is the highest contrast. So its no accident that most books are in black and white. There is a plethora of research on perceptual processing which is easily found on google scholar if you which to investigate this further.

Colour and Reading In 1984 a study was conducted comparing 24 colour combinations of text and back ground, this was of course on an older monitor, but there wasn't any significant difference between individuals in there ability to detect text targets relative to colour different colour combinations. This included black and white. However research with colour contrast, has found that variations in contrast of colour rather than colour itself influence reading speeds, and errors in reading. Greater colour contrast between text and back ground is reported to enhance speed of reading and reducing errors. In addition improving speed of reading, high colour contrast has been found enhance retention of text based information when compared to lower colour contrasts.

fig 1. low colour contrast

fig 2. high colour contrast

In addition to colour, contrast in luminescence (lightness) between text and background also influences readability. According to Knoblach et al (2001) high contrasts in luminescence between background and text enhances reading speed to a greater degree than colour contrast, although colour contrast keeps reading speed high when luminescence is low. In other words greater differences in the lightness and the colour of text and background is optimum for reading ability. Industrial researchers have taken this further with a 2009 study by Hewlett Packard (HP) specifically stating that 30 units CIE lightness contrast is optimum for reading rates and reduced error, this is not the highest contrast, although still high. However high colour contract and luminescence contrast are not additive, as they are coded in the same way in the visual system. Essentially so as long one of the contrasts is high reading speed and errors should low, meaning you don't need to use back on white.

What I haven't discussed here the two systems which process light: the magnocellular and parvocellular systems. So yes we are hardwired to process colour differently from grayscale.

fig 3. Diagram of Visual system

note. Mi = Magnocelluar (grayscale, low resolution, movement) Pi = Parvocelluar (colour and high resolution)

The magnocellular visual pathway which is dominate for processing text, and uses gray scale (black to white). However dyslexics, like myself, appear to have a preference and adaption toward utilising the parvocellular visual pathway (colour processing). This is likely due to differences in visual processing using the magnocellular system between controls and dyslexics, which suggests that dyslexics do not process greyscale as well as non-dyslexics. However this isn't to say that you need to be dyslexic to prefer processing with the colour system than grayscale. THIS SECTION IS SPECULATION BASED ON NEURAL MECHANICS There is also the possibility that prolonged activation of the magnocelluar system, by reading, may fatigue the neurons or/and photoreceptors, consequently reducing ease of reading. Hence why e-readers tend to use grey backgrounds.

Summary

There is more stuff to add in about positive and negative contrasts, for instance there is little difference in reading ability for black on white in comparison to vice versa. Overall, however, there is little difference in reading performance so long as colour and luminescence contrasts are high, meaning that black on white (highest contrast in both) is not necessarily better. Some individuals have a preference for using colour over grey scale, which while activating different visual pathways is still coded similarly for contrast in the brain. The preference against black on white may be due to the fatiguing nature of over activation of neurons in the visual pathways, or other factors such as dyslexia.

Answer 2

As Waldemar said, it is has a natural reason. During long evolution the eyes are adopted to acquire information through shadows around the objects, but it works also in reverted mode (light object on a dark background). However it is understood that the eye cannot work in two modes at the same time (normal and reverted), so black text on light background is just the more natural way, since we are "day" animals and most of the time we need dark objects/contours and light backgrond to acqure information effectively.

Interestingly there are anecdotes told, that a dark theme reduces the eye strain. This is a typical fallacy: a user sets a dark theme and sees much less light - at a first glance it reduces the strain, but if you need to read the text and not only stare at the screen, it turns out that it is just very unnatural way. No matter how does one play with colors, black text on light background will always win. And in a low lighted room, one just need to tune the background color, but it never should go in the reverted mode, if you really care about your eyes.

Also I have read some experimental reports that people with certain impairments are known to find it easier to read with reverted contrast. I personally could believe in this, but again, I am very very skeptical about that.

I just think that in most cases those experiments just lack the appropriate setup and proper question formulation. I doubt that using dark theme can be any good solution for patients with such impairments. I suppose there can be some very rare case, if a patient has some kind of "reverted" vision, which means he can see better in reverted contrast, which in turn IMHO is very uncommon, at least I have never ever heard about it. In such a case I would say, it is a very severe impairment, and can only evoke pity.

In other words I suppose that the percent of people, who really can read better with reverted contrast is very small, I would speculate the percentage must be a number with many zeroes after the dot.
So if someone claims that light text on dark ground is better readable, almost sure he is talking rubbish and is damaging his own eyes without even understanding it.

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FOLLOWUP

Regarding the question, if B on W is really better than W on B, one can find enough clarifications, similar to the given above. One article with a self-explaining title: "Positive display polarity is advantageous for both younger and older adults"

http://www.tandfonline.com/doi/abs/10.1080/00140139.2013.790485

Conclusion of the study: "... The presentation in positive polarity is recommended for all ages. ..." This is just something that one need to accept and stop searching for something that is not there.

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I'll just put here a list of related misbeliefs:

• B on W is better because historically people used black ink on a light medium and got used to it.

While the latter is true, it is still not the reason, and the reason lies much deeper in our nature.

• Dark background causes less eye strain.

Ok, but where is the information we read then? One reads through patterns (words) and not some abstract blobs, one needs sharp details for effective decoding.

• In a dark environment use a dark theme.

Just forget about the dark environment, buy a lamp and set up a comfort lighting.

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I was experimenting a lot and reading on the subject of optimal text/ground color, but I've never doubted that inverted contrast is a bad idea for text, regardless of the media and lighting.

For me much more interesting is, which ground color is actually optimal on a monitor? I mean optimal for reading text in normal conditions - in a room with normal lighting (not too dark, but no bright sun).

After comparing my experience with opinions found in the web and from some of my coworkers, which I use sometimes as experimental persons :) it turns out that this optimum is indeed quite narrow.

So this is my personal choice for the background color, and it is similar to other's personal preferences:

Note the value of the color, #E6E8DC and especially the Hue value: 73 degrees. (This color picker is in Photoshop, other programs can use other HSB ranges and units.)

So my statement is, if you start with this color, you'll be not far from the optimum, which of couse can vary in some range.

How could it be theoretically supported? I don't know actually, but here is an interesting, let's say, coincidence: Let's consider the book "Sensation and Perception" by E. Bruce Goldstein, Page 56 (https://books.google.de/books/about/Sensation_and_Perception.html?id=2tW91BWeNq4C&redir_esc=y)

Here one sees the visual stimuli peak depending on light wavelength. Interestingly this peak lies exactly on the same Hue range, which I found most comfortable for reading (compare with previous image). And the farther from this Hue value, the worse was my reading experince.

Does this explain something on a low-level? Well it should provide more contrast in terms of stimuli. But why this particular Hue value, I don't know, but it is still very interesting. Probably it has also something to do with evolution: mixing the color of sand, green vegetation, brown leaves could give something similar to this color Hue. Anyway, this color optimum is something that I can setup for me easily on a computer.

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Now going back to the original question:

• Why dark on light is easier? Namely, how does it come so?

This is an interesting question, and I think in general it can be explained as the natural evolution. Just think of millions of years of evolution and these things:

• A crab on the sand
• A bug on a leaf
• A structure of a tree or cracks on a stone

To make a parallel with reading it is better to think of the last example - a crack on a stone. This is statical information about an object, its form, exactly what we need to decode a text piece.

There are also counter examples - e.g. light hay on the dark ground, but such things simply are less common in our world. So here lies the answer -

we treat the objects by dark contours and shadows simply because these represent dominant forms, or patterns in the nature. To be more exact, those patterns which are important for our life and activity.

If a creature evolves in other environment, like deep sea or a cave, then it can come to other principles of course.

A good example is this test from the same book "Sensation and Perception", page 109. This test is used for slightly other purposes, but it shows the general principle:

Answering the question, one can notice that one tends to identify the dark areas as objects, not the light ones, despite they are formed by the same curves.

Answer 3

I know this thread is old. I thought I'd mention another thing, which is that white on black exposes visual imperfections much more than black on white. No matter how good you think your vision is, it has a point spread function which is imperfect. That is, a very bright white point of light will not actually look like a perfect dot. It will be smeared, or doubled, or a star/asterisk, or some combination of all of these. If your vision is great, the dot may have to be brighter to expose this, but it's always there. White on black makes it very apparent, where with black and white, the black text just gets a little bit lighter and it's not really annoying. The effect is exacerbated by the fact that with black backgrounds, your pupil will dilate more, making the distortion worse (even people with bad eyes can often see well in the bright of day when their pupil is tiny).