science

Image persistence

Image persistence is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Image persistence rather than just read about it. In short: Image persistence, or image retention, is a phenomenon in LCD and plasma displays where unwanted visual information is shown which corresponds to a previous state of the display. It is the flat-panel equivalent of screen burn-in.

Key takeaways

Image persistence belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Image persistence to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Image persistence from memory before moving on to harder problems.

Reference excerpt

Image persistence, or image retention, is a phenomenon in LCD and plasma displays where unwanted visual information is shown which corresponds to a previous state of the display. It is the flat-panel equivalent of screen burn-in. Unlike screen burn-in, the effects are usually temporary and often not visible without close inspection. Plasma displays experiencing severe image persistence can result in screen burn-in instead. Image persistence can occur as easily as having something remain unchanged on the screen in the same location for a duration of even 10 minutes, such as a web page or document. Minor cases of image persistence are generally only visible when looking at darker areas on the screen, and usually invisible to the eye during ordinary computer use. If an image updates every millisecond, it can take 2 minutes for a defective LCD screen, or 10 minutes for a normal LCD screen, instead of 6 minutes for a defective one or 4 hours for a working one.

Cause Liquid crystals have a natural relaxed state. When a voltage is applied they rearrange themselves to block certain light waves. If left with the same voltage for an extended period of time (e.g. displaying a pointer or a taskbar in one place, or showing a picture for an extended period of time), the liquid crystals can develop a tendency to stay in one position. This ever-so-slight tendency to stay arranged in one position can throw the requested color off by a slight degree, which causes the image to look like the traditional "burn-in" on phosphor-based displays. The cause of LCD image retention is different from phosphor aging as in CRTs, but the visual phenomenon is the same: uneven use of display pixels. Slight LCD image retention can be recovered. When severe image retention occurs, the liquid crystal molecules have been polarized and cannot rotate in the electric field, so they cannot be recovered. Severe image retention on an LCD manifests as a ghostly, persistent afterimage—akin to a translucent, three-dimensional shadow—of content that remained static on the screen for an extended period. This ghosting is caused by the temporary polarization or "sticking" of the liquid crystal molecules within specific pixels. When a static image (like a taskbar, logo, or document outline) is displayed, the voltage applied to those pixels holds the liquid crystals in a fixed orientation for too long. The cause of this tendency is unclear. It might be due to various factors, including accumulation of ionic impurities inside the LCD, impurities introduced during the fabrication of the LCD, imperfect driver settings, electric charge building up near the electrodes, parasitic capacitance, or a DC voltage component that occurs unavoidably in some display pixels owing to anisotropy in the dielectric constant of the liquid crystal.

Prevention and treatment Image persistence can be reversed by allowing the liquid crystals to relax and return to their relaxed state, such as by turning off the monitor for a sufficiently long period of time (at least a few hours). For most minor cases, simply continuing to use the computer as usual (and thus allowing other colors to "cover" the affected regions) or turning off the monitor for the night is more than enough. One strategy for users looking to avoid image persistence artifacts is to vary the activities performed on a computer to avoid static colors and hide elements on the screen which are displayed perpetually (such as an OS's taskbar). Another strategy is the usage of a screensaver to help during times the computer is left unattended. Covering the entire display area with pure white for an extended period of time is also a useful proactive solution. Several monitor manufacturers (notably Dell) includes a built in setting which cycle through multiple colors. Dell encourages to leave this setting on for several hours if there are signs of image persistence. Some LCD displays may also cycle through colors while the display is on sleep mode (the backlight is off) with the idea that the visibility of image persistence is reduced when the display is in use later on.

References

External links Article on LCD image persistence Archived 2005-12-11 at the Wayback Machine TFT LCD Burn-in

Illustrations

Worked examples

Example 1 — a first encounter with Image persistence

Start with the simplest possible case. Write down what Image persistence claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Image persistence before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Image persistence ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Image persistence

In research: Image persistence appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Image persistence in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Image persistence is common in secondary-school and first-year university syllabi. It links to neighbouring topics Display technology, Liquid crystal displays, so understanding it makes those chapters shorter.
In everyday life: Look for Image persistence outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Image persistence” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Image persistence in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Image persistence means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Image persistence out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Image persistence in simple terms?

Why does Image persistence matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Image persistence?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Image persistence.