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An LCD with LED-Backlight may be edge- or direct-lit: [9] edge-lit (ELED): LEDs form a line around the rim of the screen. May additionally support: frame dimming: adjusts the brightness of the entire backlight based on the content displayed, as if local dimming was supported but only with a single zone
The LCD panel is synchronized with the backlight. For example, to make a segment appear red, the segment is only turned ON when the backlight is red, and to make a segment appear magenta, the segment is turned ON when the backlight is blue, and it continues to be ON while the backlight becomes red, and it turns OFF when the backlight becomes green.
A backlight is a form of illumination used in liquid-crystal displays (LCDs) that provides illumination from the back or side of a display panel. LCDs do not produce light by themselves, so they need illumination ( ambient light or a special light source) to produce a visible image.
Burn-in on a monitor, when severe as in this "please wait" message, is visible even when the monitor is switched off. Screen burn-in, image burn-in, ghost image, or shadow image, is a permanent discoloration of areas on an electronic visual display such as a cathode-ray tube (CRT) in an older computer monitor or television set.
A dark dot defect is usually caused by a transistor in the transparent electrode layer that is stuck "on" for TN panels or "off" for MVA, PVA, and IPS panels.In that state, the liquid crystal material does not do any rotation so that the light from the backlight does not pass through the RGB layer of the display.
Before the advent of LCD screens, most computer screens were based on cathode-ray tubes (CRTs). When the same image is displayed on a CRT screen for long periods, the properties of the exposed areas of the phosphor coating on the inside of the screen gradually and permanently change, eventually leading to a darkened shadow or "ghost" image on the screen, called a screen burn-in.
Backlight intensity is usually controlled by varying a few volts DC, or generating a PWM signal, or adjusting a potentiometer or simply fixed. This in turn controls a high-voltage (1.3 kV) DC-AC inverter or a matrix of LEDs. The method to control the intensity of LED is to pulse them with PWM which can be source of harmonic flicker.
When a photodiode is exposed to a very bright light source, the accumulated charge can spill over into adjacent pixels, creating a halo effect. This is known as "charge bleeding." The bloom effect is more pronounced in cameras with smaller pixels, as there is less room for the charge to dissipate.