Thursday, September 1, 2011

Backlit vs. frontlit

Has anybody seen any studies regarding why many people feel discomfort from reading a long time on a backlit screen which they don't feel reading on a reflective screen like E-Ink? (Kindle.)
If we assume that the screens are adjusted to give the same amount of light out, what is the difference? Light is light, no? Do modern LCD screens flicker? Or... ?

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As to why I so dislike the grey E-Ink screen when most seem fine with it?...

Well, I do have good reading lights. But I'm still looking at black on grey.

Maybe the thing is that I feel I want the background of my reading to be roughly the brightest thing in my field of view (not much brighter though), since this is the thing I want to focus on.

That sounds likely. But all I know is that the irritation is there, and it keeps being there.

14 comments:

Stephen A said...

Speaking as a Ph.D. in Physics with a specialization in optics and considerable experience in backlight construction and display evaluation. Light is never just light.

Backlights are the main poer consumers in tablets and their optimization is one of the primary contributors to battery life.

Backlights have differing spectral distributions, either corresponding to cold cathode florescent lamps (CCFL) or LED sources. The "white" that you see is generally skewed heavily to the blue.

The angular distribution of light is rather specific too. The bulk of the light is concentrated perpendicular to the screen so that it reaches the reader as opposed to lighting the walls or ceiling. Next time you have your tablet in a darkened room shine it on the wall and look how concentrated the light is. (tablets actually make pretty good "softbox" lighting for photography). Screens meant for laptops, TVs,and monitors generally tailor the light to form a slit along the wide side.

While IPS displays are remarkably angle independent older TFT displays have a strong angle dependent contrast ratio. Flicker is a negligible factor.

Electrophoretic (eInk) displays are much more lambertian (i.e. they scatter light in all directions) and have a spectral distribution and brightness equivalent to the surrounding lighting.

The psychophysical impact of backlit displays is very complex. In particular having a bright screen with a very dark room (under 20%) causes considerable eyestrain. The color distribution can have effects as well.

Len Edgerly said...

Stephen, that's fascinating info on the difference between backlit and electrophoretic screens. It confirms my own personal sense after three years of reading exclusively on a Kindle that my eyes (and even my mind, somehow) relax when I leave my computer screen and pick up the Kindle. Maybe it's years of equating reading books on paper with relaxed, contemplative settings and mood (except for school books, a whole different story). Thanks for asking the question, Eolake!

Timo Lehtinen said...

In particular having a bright screen with a very dark room (under 20%) causes considerable eyestrain.

In my subjective experience, this is the main issue. But I also suspect that with ambient light level matched to screen brightness, the distorted spectrum of the backlight (that Stephen wrote about) would then be the main annoyance.

So, most of the time, the quality of the viewing experience is so bad in terms of contrast, that we don't pay attention to the tonal range. But we would, if only the whole scene was lit better.

eolake said...

Thanks, fellows.

In the past couple years I've paid more attention to that balance, and on running my displays and iPad on less than full brightness.

I hope that they will invent near-white e-ink backgrounds soon.
And also backlit displays which are less bothersome, whatever it'll take.

Jim Van Donsel said...

It would be interesting to know what is the limiting factor in the whiteness of the background in eInk.

Is it the oil medium itself? Or a smattering of ink spheres in the wrong state? Or broken spheres that have spilled their black particles into the oil?

eolake said...

indeed interesting, and a bit odd.
I'm pretty sure it's none of the two last ones. It would be uneven.

And clear oil should not be hard to find.
Neither should white plastic for the little balls for that matter. So maybe it's something with light being broken up between the small particles and the medium...

But yeah, interesting. I was the least thing I would have expected to be a problem, I would have thought it would be precision and evenness.

eolake said...

http://en.wikipedia.org/wiki/E-ink

Maybe it is the spaces between the containing balls. Or that the particles can't fill the whole top half of the balls, thus also giving a colorless space.

Timo Lehtinen said...

I don't understand the problem you have with E-ink background color. The paper stocks used in physical books are almost never white either. And there is a wide consensus that min-black on max-white is not ergonomic for the eye.

Even your own website has a gray background.

eolake said...

I understand your confusion.

Web sites are backlit, plenty of contrast to take from.

I don't prefer pure white. I prefer a shade darker. But the Kindle background is *several* shades darker, almost middle-grey.

It seems clear that I'm in a minority with this problem, it's rarely mentioned. But it just bothers me, what can I say. I need to find really dang good light to read comfortably on the Kindle 3.

Maybe it's that it doesn't feel like the page reaches out to me, I have to strain towards *it*.

I *really* wanted to love the K3, and for a while I did, in some ways still do (perfect hand size).

Timo Lehtinen said...

I haven't seen a Kindle, but I saw a Sony ereader (with E-Ink screen) in a bookstore the other day. I played with it a little, specifically to inspect this problem that you have so often mentioned. And I must say the screen looked perfectly readable to me.

Granted the bookstore had bright fluorescent lights on the ceiling. Maybe in a more dimly lit room it might become a problem. But then, so would reading a paper book.

Maybe you need to improve the lighting conditions in your apartment?

Personally, what bothers me much more about the Kindle is its closed architecture. I.e. being too tied to the Amazon store.

eolake said...

I have good reading lights. But I'm still looking at black on grey.

Hmmm, maybe the thing is that I feel I want the background of my reading to be roughly the brightest thing in my field of view (not *much* brighter though), since this is the thing I want to focus on.

That sounds likely. But all I know is that the irritation is there, and it keeps being there.

(By the way, maybe white would be best after all, studies be damned. After all, "white" and "white" are two things, you can adjust the lighting, and white would give a greater range of that.)

Well. We'll see what future screens, reflective as well as backlit, brings us. I have a feeling it can be much better than anything we've seen.

eolake said...

"Personally, what bothers me much more about the Kindle is its closed architecture. I.e. being too tied to the Amazon store."

This is unfortunate, yes. As is that the Kindle can't read ePub.
But Amazon has been smart in providing reading software to a host of devices, and this pulls them in, including me.
Too many books can be found for Kindle and nothing else, otherwise I'd love to use MegaReader for example, which is much better software.

Timo Lehtinen said...

I have a feeling it can be much better than anything we've seen.

You don't say, technology is going to improve from what it is now?!

;-)

eolake said...

I don't usually have that feeling. I guess it's just poor imagination.