johns1,
johns1 wrote:
High-Death
DrAndyWright,
The Retina Display as any other LCD display from APPLE and most other brands nowadays is LED-Backlit display, all of them. therefore they all use phosphors and phosphors are responsible for ghosting, Image Retention, Flicks and some other issues related to PWM (Pulse-Width Modulation). I can link a post from the the AVS Forum where i discuss that if you want. But good that you now acknowledge, even if still in confusion, that IR is standard for LCDs.
The actual LCD doesn't utilize phosphors, while the LED backight light source does. I am not sure how you arrive at the conclusion that phosphors is responsible for ghosting and imaging retention with LCD panels.
reference LED Backlighting for LCDs: Options, Design Considerations, and Benefits
Now if one looks at the LCD image persistence (ghosting)tech note from Leveno, you can see they are discussing what actually causes IR.
"Generally (Twisted Nematic- TN type) LCDs have a parallel electrical field, so all of the display area can be symmetrically controlled. By comparison, IPS LCDs have asymmetrical electrical fields in some small areas, the image persistence phenomenon will occur at the asymmetrical electric fields. The image will dissipate during power off or by an image change in a short amount of time. This phenomenon is a natural characteristic of an IPS LCD."
IMHO both the LG AH-IPS and the Samsung ISP varient (PLS) would be subseptable to image persistance in varying degree's.
BTW I am a very old and active poster in AVSforums and go by a another handle. You have to take with a grain of salt whats posted there also. 😉
Your quote form my text clearly shows that I said that LED-Backlit displays use phophors, so you are just repeating what I said (and you even quoted) when you says that Led-Backlit LCD are the only ones that use phosphors. All APPLE LCDS are LED-Backlit, so therefore you are completely wrong when you say that the ACTUAL (that doesn't mean anything actually) LCD do not use phosphors. We are talking about Apple displays and the Retina Displays, and they all are Led-Backlit displays that use phosphors on the blue LED.
Oh and BTW, about your "this is what causes ghosting on LCD", LED-Backlit displays and LED displays came to reduce this "Image Persistance", the image persistance you are describing (or actually quoting from the article you linked) is not the persistance you are seeing here. That persistance is related to the active eletrical field that does not go off uniformly and then requires a CHANGE IN THE IMAGE or a complete TURN OFF of the display. This is not the case here, what everybody is describing is a Persistance where a retention of the image lasts for a while eventhough you TURN IT OFF, Change the picture OR NOT. It will dissipate by itself. Now read again your paper and see if this is the "Image Persistance" described there?? It is clearly not, but it is good that you acknowledge as well (like the Apple Geniuses said) that LCDs suffer from many kinds of "Image Retention"
Just to confirm every Apple display is Led-Backlit (http://en.wikipedia.org/wiki/Backlight):
In October 2008, Apple announced it will be using LED backlights for all its notebook and its new 24-inch Apple Cinema Display, and one year later it introduced a new LED iMac, meaning all of Apple's computer screens are now LED. Almost every laptop with 16:9 display introduced since September 2009 uses LED-backlit panels.
Where did I get to the conclusion that phosphors are resopnsible for ghosting??? Have you heard about plasma displays? If No, lets first quote Wikipedia (http://en.wikipedia.org/wiki/Screen_burn-in):
With phosphor-based electronic displays (for example CRT-type computer monitors or plasma displays), non-uniform use of pixels, such as prolonged display of non-moving images (text or graphics), gaming, or certain broadcasts with tickers and flags, can create a permanent ghost-like image of these objects or otherwise degrade image quality. This is because the phosphor compounds which emit light to produce images lose their luminance with use. Uneven usage results in uneven light output over time, and in severe cases can create a ghost image of previous content. Even if ghost images are not recognizable, the effects of screen burn are an immediate and continual degradation of image quality.
The length of time required for noticeable screen burn to develop varies due to many factors, ranging from the quality of the phosphors employed, to the degree of non-uniformity of sub-pixel usage. It can take as little as only a few weeks for noticeable ghosting to set in, especially if the screen displays a certain image (example: a menu bar at the top or bottom of the screen) constantly, and displays it continually over time. In the rare case when horizontal or vertical deflection circuits fail, all output energy is concentrated to a vertical or horizontal line on the display which causes almost instant screen burn."
Then lets quote more form SAMSUNG:
Displaying stationary images that exceed the above guidelines can cause uneven
aging of LED Displays that leave subtle, but permanent burned-in ghost images in the LED picture.
We have already read about screen burn-in in the first quote, right? But one more interesting comment form the same article:
...This is partly because those screens displayed mostly non-moving images, and at one intensity: fully on. Yellow screens are more susceptible than either green or white screens because the yellow phosphor is less efficient and thus requires a higher beam current.
The Yellow phosphor is exactly the phosphor being used for the blue LED in theLED-backlit displays (http://en.wikipedia.org/wiki/Backlight):
A white LED is typically a blue LED with broad spectrum yellow phosphor to give the impression of white light. Since the spectral curve peaks at yellow, it is a poor match to the transmission peaks of the red and green color filters of the LCD. This causes the red and green primaries to shift toward yellow, reducing the color gamut of the display.
And about Flickering and PWM that I have said before (http://en.wikipedia.org/wiki/LED-backlit_LCD_television):
"LED backlights are often dimmed by applying pulse-width modulation to the supply current, intended to switch the backlight off and on faster than the eye can perceive. If the dimming pulse frequency is too low or the user is very sensitive to flicker, this may cause discomfort and eye-strain, similar to the flicker of CRT displays at lower refresh rates.[citation needed] This can be tested by a user simply by waving a hand in front of the screen; if it appears to have sharply-defined edges as it moves, the backlight is pulsing at a fairly low frequency. If the object appears blurry, the display either has a continuously-illuminated backlight or is operating at a frequency too high to perceive. Flicker can be reduced or eliminated by setting the display to full brightness, though this gives worse image quality and increased power consumption."
And now about phosphors (http://en.wikipedia.org/wiki/Phosphor):
For white LEDs, a blue LED is used with a yellow phosphor, or with a green and yellow SiAlON phosphor and a red CaAlSiN3-based (CASN) phosphor.
The Yellow Phosphor:
(Y,Gd)3Al5O12:Ce3+
The Yellow Phosphor Persistence: MEDIUM
More about phosphors (http://www.wiley-vch.de/books/sample/3527314024_c01.pdf):
Here the excitation mechanism strongly resembles the one in
cathode ray phosphors. Phosphors for Light-Emitting Diodes (LEDs) and phosphors
for Plasma Display Panels (PDPs) are treated separately as well, the processes leading
to excitation and emission being comparable to those in fluorescent lamps.
Self-absorption is also an important loss factor in luminescent structures which do not effectively scatter the luminescence light. This is the case, e.g., in organic or inorganic LEDs, where trapping of light in the luminescent structure, followed by absorption of the light emitted in the luminescent material, strongly reduces the light output.
And a complete guide that explains the Decay time, ghosting, burn-in and Image persistance due to phosphors (you can read parts on the web):
http://books.google.com.br/books/about/Phosphor_Handbook.html?id=I9O1K20-uo4C&re dir_esc=y
Anything else?