Core factors affecting LED display performance
With the rapid development of indoor LED screens, LED display is widely used in the command center, monitoring center, and even LED volume studio. However, from the overall performance of the LED display system, can these displays meet the user’s needs? Are these LED displays compatible with human vision? Can these LED screens stand the test of different camera shutters and different angles? Next, GalaxyAV will analyze factors affecting LED display performance from 2 aspects: refresh frequency and gray level.
LED display refresh frequency (visual refresh frequency)
Visual refresh frequency refers to the rate at which a screen is updated and is usually expressed in Hertz (Hz). Generally, the visual refresh frequency of a high-performance LED display is above 3,000Hz. The higher the frequency of visual refresh, the more stable the picture display and the less visual flicker. The LED display screen’s low “visual refresh frequency” leads to the horizontal stripes appearing in the camera and photography and the image of tens of thousands of LEDs flashing simultaneously. Therefore, human eyes may feel uncomfortable when watching and even cause damage to the eyes.
Although the visual refresh frequency above 60Hz can produce a continuous picture for the human eye, the higher the visual refresh frequency, the more stable the image displayed, and the less likely the human eye is to feel tired. In high-quality video, high-speed cameras are now used at speeds of more than 1,000Hz per second to get more detailed images, such as highlights or close-up photography. However, it is a big challenge to display a continuous picture (no black scan lines) or a continuous color scale at a fast shutter speed for an LED display screen.
The gray level of LED display
Gray level refers to the varying levels of color between the darkest and lightest colors. Generally, for a high-efficiency LED display, the gray scale is more than 14 bits (bit), meaning at least 16,384 color levels. If the gray level is insufficient, there will be an insufficient color level, or the gradual color level is not smooth enough, which can not fully show the picture color, so the LED display effect is greatly reduced. In addition, some low-performance LED screens can perceive a noticeable color lump distribution at 1/500s shutter speed, which will be even more noticeable if we increase the shutter speed by, say, 1/1000s or 1/2000s.
Factors affecting the refresh frequency and gray level of LED display
We know that LED display has several core components, such as LED switch power supply, LED driver, LED lamps, etc. For the refresh frequency and gray level of LED display, the LED driver directly determines the LED display performance in visual refresh frequency and gray level.
In the current LED driver, the latest technology is “ScrambledPWM(S-PWM) technology,” S-PWM technology is to improve the traditional pulse width modulation (PWM) technology; it is an image conduction time dispersed into several shorter conduction times to increase the overall visual update rate. It further explains that the new generation of LED driver chip technology, S-PWM technology, can count once (LED grain ON→LED grain OFF) of the original frame, and average shatter into multiple counts, and each shatter equal, can maintain the original ON/OFF ratio before the shatter.
The S-PWM technology provides different counting modes, thus increasing the image refresh frequency to 64 times. If we use S-PWM to improve the image refresh frequency, we can easily increase the visual refresh frequency by 64 times with 5MHz and reach more than 4,800Hz. Compared with the general video refresh frequency at least ten times higher, it can also avoid high-frequency electromagnetic interference (EMI issue), Overshoot, and Undershoot problems.
The LED display using the S-PWM driver does not show horizontal black scan lines and color block distribution even when the image is taken with a high-speed shutter of a digital camera. This is because of its visual refresh frequency, and the gray level of performance far beyond traditional switch-type driver LED display.
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