Contrast ratio, why so much difference between different LED displays
As we all know, for LED displays, contrast ratio is one of the important parameters. The greater the contrast ratio, the clearer the image, and the more colorful it is. The contrast ratio of LED displays on the market varies greatly, and the value can easily differ by several digits.
contrast ratio diffrence
According to the formula of contrast: contrast = luminous brightness (luminous brightness) / not luminous brightness (reflective brightness) can be seen, want to improve the contrast of the LED display, the main methods include increasing the brightness of the display, so that “brighter brighter”, as well as reduce the display surface light reflection coefficient, so that “darker darker”. So do you know what the reasons for the difference in contrast to small pitch LED displays include in practical applications?
Different chip sizes
Generally speaking, the smaller the chip used, the higher the contrast of the LED display.
In the same point spacing conditions, the smaller the size of the LED chip, the larger the black area, and the lower the brightness when not luminous, although the luminous area is reduced, the contrast ratio obtains a substantial increase. This is currently the most direct and effective way to improve contrast.
Under the premise of the same point spacing, the smaller the chip, the “stay black” area is larger, which can make the display overall “black more black”.
Front-mounted chips and flip-chip different
On the other hand, the contrast of the flip-chip will also be superior to the front-mounted chip. In the front-mounted LED chip, electrodes and bonding lines are on the light surface, occupying part of the area should be light, to a certain extent, will affect the LED chip light angle and luminous intensity; and electrodes and bonding lines and other metal components will also cause a sense of reflection, so that “the light when dark”, reducing the contrast of the display.
With and flip-chip, no electrodes and solder lines, and a reflective, large light-emitting area, luminous efficiency is significantly better than the front-mounted chip, so that “brighter brighter”, the contrast will usually be higher than the front-mounted chip.
In the same COB package, the flip-chip structure’s light-emitting area is larger.
SMD and COB packaging methods are different
The use of COB package products contrast ratio is often much higher than the traditional SMD package products, this is because. SMD LED bracket structure issues
SMD LED display requires the use of a bracket structure to support the chip device. However, due to the size limitation of the bracket, the package body using an SMD bracket can not continue to shrink, RGB light-emitting pixel point there is a physical limit. The large area of the luminous dots means that the surface of the LED display “black area” is small and cannot make the “black more black”, resulting in low contrast of the LED display.
And because the COB package does not exist a bracket structure, in the Mini/Micro LED chip technology, display manufacturers can use a smaller chip according to different viewing needs. The smaller the chip occupies the area on the PCB board, the larger the black part occupies the space, and the more distinct the bright black area of the LED display, which can present a blacker black field, and brighter brightness, so that the LED display contrast is higher.
In the case of the same size as the front-mounted chip, the structure of COB and the distance between the luminous pixels are better than in the SMD package.
Different measurement methods
Different ways of measuring contrast can also have a great impact on contrast data. Basically, the contrast ratio is also divided into static contrast ratio and applied contrast ratio.
The static contrast ratio is the maximum contrast ratio of a screen measured in a completely dark room environment. Generally speaking, due to the dark room environment, LED display brightness is very high, so the static contrast ratio will often be as high as dozens or even millions to one.
Application Contrast Ratio refers to the contrast ratio tested in accordance with the Light Emitting Diode (LED) display test method in the Electronics Industry Standard of the People’s Republic of China issued by the Ministry of Industry and Information Technology – the highest contrast ratio of the screen measured at an ambient illumination of 10±10% lx. According to industry standards, an LED display application contrast ratio greater than or equal to 5000:1 is the highest level of C.