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Old 07-03-2012, 02:28 PM   #31
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Originally Posted by HarryT View Post
Rationally speaking, there should be absolutely no difference between reading from an eInk screen or reading from a backlit screen whose brightness is correctly set.

I can only think that people who complain that they can't use backlit screens perhaps have the brightness set too high?
Everything about human-machine interaction is complex, and the complexity mainly comes from the "human" side of interaction. First, every person reacts differently, and second, our eyes have a weird tendency to favour certain lightning conditions. For example, we prefer daylight to most artificial sources of lightning, regardless of the luminosity or the energy delivered in process.

I am not certain what is the exact source of problems with backlit use, it might be something as simple as refresh cycles that we don't really "see", but still can tire our eyes after prolonged use.
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Old 07-03-2012, 03:47 PM   #32
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I am not certain what is the exact source of problems with backlit use, it might be something as simple as refresh cycles that we don't really "see", but still can tire our eyes after prolonged use.
LCD screens don't have "refresh cycles"; their display is constant, just like eInk, until it explicitly changes. An LCD display doesn't flicker, like a CRT does.
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Old 07-03-2012, 04:45 PM   #33
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Originally Posted by HarryT View Post
LCD screens don't have "refresh cycles";
Are we referring to the same thing?

The decision to change a pixel (or not) still happens periodically, most of the modern OS'es will show "refresh rate" of the monitor, which is, if I am not mistaken, the mode of operation defined/limited by the panel's capabilities. Isn't the crystal "re-polarized" (gross simplification) every refresh cycle?
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Old 07-04-2012, 12:12 AM   #34
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I think Harry's question is: Has it been shown the using backlit displays affects sleep patterns, or has it been shown that using a display of a particular brightness affects sleep patterns? If you shone a bright enough light onto a reflective display so that the light output equaled that of the backlit display, would there be any difference?
If the study was done properly (and I haven't actually tracked it down and read it), they should have controlled for brightness levels. Based on the researchers I work with, I'll give the people that did that study the benefit of the doubt that they did unless I see otherwise. I've sat through enough talks and job talks in my department to know that someone that didn't do that would likely be skewered and roasted slowly over the coals.

Bah, now I think I'm going to have to spend some time tracking it down to read it.
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Old 07-04-2012, 12:31 AM   #35
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I think Harry very likely has hit the nail on the head with his comment on brightness. Most backlit screens are generally multi-purpose and used for instance to read comics and watch movies. Higher brightness levels make the colours "pop" and gives more life to movies and such and when the time comes to read a book how many think of adjusting the brightness?

Having said that, I think Ankh is right on the money too when (s)he (?) says that "Everything about human-machine interaction is complex". Human responses to stimuli are often inexplicable, or can only be explained partially, in scientific terms. Just visit a Hi-Fi forum sometime, to witness protracted discussions/violent arguments over which piece of cable is better suited to connect two audio components.
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Old 07-05-2012, 01:44 AM   #36
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Originally Posted by Ankh View Post
Are we referring to the same thing?

The decision to change a pixel (or not) still happens periodically, most of the modern OS'es will show "refresh rate" of the monitor, which is, if I am not mistaken, the mode of operation defined/limited by the panel's capabilities. Isn't the crystal "re-polarized" (gross simplification) every refresh cycle?
Yes, the display has a refresh rate, but it doesn't flicker at that rate as a CRT does. The display is flicker-free, just like eInk.
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Old 07-05-2012, 11:20 AM   #37
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About flicker: wrong. Lcds do flicker, crts were more noticeable because they are interlaced displays that change their screen at 30 Hz since they have to use up half of their refresh rate changing the interlacing (and there is a slow decay inherit to the technology, plasmas also have this decay that is what makes plasmas look more crt like than lcds). Lcds refresh the screen at 60 Hz minimum. It still flickers just so fast that we can't see it.

About eye strain: this doesn't require physics. When the screen is brighter than the surrounding environment it is easier to get eye strain because it is harder to focus on something else in the room from time to time. That is why I use a backlight when I watch tv, and I use autodim on my iphone. A kindle reflects the light, and is thus always the same intensity as the rest of the room... so it is harder to get eyestrain reading on it.
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Old 07-05-2012, 11:26 AM   #38
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About flicker: wrong. Lcds do flicker, crts were more noticeable because they are interlaced displays that change their screen at 30 Hz since they have to use up half of their refresh rate changing the interlacing (and there is a slow decay inherit to the technology, plasmas also have this decay that is what makes plasmas look more crt like than lcds). Lcds refresh the screen at 60 Hz minimum. It still flickers just so fast that we can't see it.
I'm sorry to disagree with you, but I really must. LCD screens do not flicker. They are refreshed 60x a second, yes, but there is no "decay" in light output from one refresh cycle to another. All that an LCD pixel is, in effect, is a coloured filter that allows through the (constantly illuminated) backlight that's behind the LCD. The LCD screen itself emits no light; it merely filters (and colours) the backlight.

From Wiki:

Quote:
Refresh rate or the temporal resolution of an LCD is the number of times per second in which the display draws the data it is being given. Since activated LCD pixels do not flash on/off between frames, LCD monitors exhibit no refresh-induced flicker, no matter how low the refresh rate.
(emphasis mine)
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Old 07-05-2012, 12:35 PM   #39
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Check flicker-free on Wikipedia:
Quote:
Contrary to popular belief, modern LCD monitors are not flicker free, since most of them use PWM for brightness control. As the brightness setting is lowered, the flicker becomes more noticeable, since the period when the backlight is active in each PWM duty cycle shortens. The problem is much more pronounced on modern LED backlit monitors, because LED backlight reacts faster to changes in current. Many users have reported headaches, eye strain, nausea, and other problems.
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Old 07-05-2012, 12:36 PM   #40
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Thanks, Tommy - that's very interesting, and I've learnt something new. Do you know if that same technology is used in backlit tablets, such as the iPad?
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Old 07-05-2012, 12:41 PM   #41
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Anything with colors or pictures, the iPad.

Everything else, don't care.
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Old 07-05-2012, 12:42 PM   #42
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Thanks, Tommy - that's very interesting, and I've learnt something new. Do you know if that same technology is used in backlit tablets, such as the iPad?
No idea. This was new for me also and I learnt it while googling flicker-free earlier today. I could not find anything about tablets and phones which was what I was interested in.
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Old 07-07-2012, 03:50 AM   #43
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