1.LCD structure and work flow
LCD screen(Liquid Crystal Display) plays an important role in the MSLA/LCD resin printers. In this article, I am going to introduce some knowledge bases about the LCD panel to help you learn more about resin printers.
A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical devices that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly, instead of using a backlight or reflector to produce images in color or monochrome. and it is usually made by professional manufacture such as Sharp、JDI、BOE、Samsung etc.
This picture shows the structure inside LCD, you can see there are many complex modules and electronics.
There is a YouTube video that explains very detailed info about how LCD works. different from the original LCD, the LCD used in resin printers don’t need a backlight, because we use the UV LED as a light source.
The signal interface is also different with different size LCD, there are MIPI, RGB, EDP, and LVDS. In the current resin printer market, most screens are come with MIPI(small size) and eDP(large size) interface.
With the same interface, you will also need to know if need an adaptor to connect the screen to the board sometimes. Like Sharp04 to 03interface on board(Original Photon board only support 03 interface, you will need a MIPI to MIPI adaptor to work with current Sharp04 screen)
The ChiTu L series use the MIPI interface, you can connect directly with a small size LCD panel.
The ChiTu L HDMI series use the HDMI interface, you will need an HDMI to eDP adaptor to work with a large-size LCD panel.
2.LCD Screen size and Pixel
The screen size is the size of the diagonal measurement.
The Pythagorean theorem also work on this: width²+height²= (diagonal measurement)²
For example, a 5.5inch 2K Sharp04(LS055R1SX04) screen’s LCD active area is 68.04mm(H)x120.96mm(V), which marks as 120*68 printing size in the printer’s specification.
68.04mm²+120.96mm²=138.78mm²
1inch=2.54cm=25.4mm
138.78mm/25.4mm=5.46≈5.5 inch
Aspect ratio refers to the width of the screen in relation to its height
In the width and height, there are the same ratio of pixels,
For example, 5.5inch sharp04 is 2K=1440pixels x 2560pixels=9:16
Here is a video introducing how different aspect ratio affects.
3.Resolution & PPI
The resolution of an LCD is expressed by the number of columns and rows of pixels (e.g., 1440×2560).
The resolution is actually the size of pixel，below is the specification of 5.5inch 2K Sharp04(LS055R1SX04) screen, which used on most 5.5inch printers such as ELEGOO Mars; Mars pro and Creality LD-002R; EPAX X1; Wanhao D7 etc. And Sharp03(LS055R1SX03) for photon and photon S, which can work with sharp04 with a 04 to 03 adapter.
Resolution = pixel size= Active area/ Pixels
68.04(H)/1440(H)=120.96(V)/2560(V)=0.04725mm=47.25μm
PPI(Pixels per inch) is the pixels in an inch. It is also using the Pythagorean theorem to calculate. Higher PPI means better resolution.
Each pixel is usually composed of 3 sub-pixels, a red, a green, and a blue one. This had been one of the few features of LCD performance that remained uniform among different designs.
Each sub-pixels can reach 256 different brightness to change the mixed color, 256x256x256=16,777,216 colors are the value that an LCD can archive.
4.Brightness and Contrast Ratio
Contrast ratio is the ratio of the brightness of a full-on pixel to a full-off pixel.
The LCD itself is only a light valve and does not generate light; the light comes from a backlight that is either fluorescent or a set of LEDs. Brightness is usually stated as the maximum light output of the LCD, which can vary greatly based on the transparency of the LCD and the brightness of the backlight. In general, brighter is better[citation needed], but there is always a trade-off between brightness and power consumption.
5.Transmission and lifespan
As we know now there are so many complex modules and electronics inside the LCD panel, most of the light will be blocked,
The LCD manufacture said that the transmission is around 1% for normal RGB LCD under 405nv UV LED light source. The lifespan is also very shorter work with UV light,
To solve this issue, LCD manufacture is trying hard to improve the transmission such as increasing the aperture ratio, also there comes out a monochrome LCD screen that can reach about 6% transmission, With better lifespan and better printing speed.
Chitusystems has a UV meter can test if your screen has dead pix.
And we have most resin screen kit on store, you can check out which you need.
