An overview of positive and negative mode LCD displays
LCD screens (Liquid Crystal Displays) have two options or display modes. positive mode (dark characters on a light colored background) and negative mode (lighter colored characters on a darker background).
See Fig. 1: Yellow-green STN (Super Twisted Nematic) display, the yellow-green background is lighter than the dark blue characters. is a positive mode . Fig. 2 is a blue STN screen, its blue background being darker than the white characters. It is negative mode.
positive mode LCD
Positive mode displays have the advantage of having a lighter background and no backlighting is required. They typically use transflective or reflective polarizers and have lower power consumption. They can be seen in ambient light.
negative mode LCD
Negative mode displays need backlighting to be seen. They normally use transmissive polarizers. They have better contrast and wider viewing angles in the dark indoor environment. Readability is much better than positive screens .
But under bright ambient light or even direct sunlight, the screens will wash off easily. To be seen in bright ambient light, the backlight brightness must be increased to more than 800 nits. Sunlight readable displays consume a lot of power.
What is better, positive or negative LCDs?
That depends on your application.
You can choose positive LCDs if you are looking for:
– Low cost;
– Low power consumption with the battery as the main power source;
– Use outdoors or in bright ambient light.
You can choose negative LCD screens if you are looking for:
– Indoor or low light environment used;
– Sharp or striking images or contrast with better viewing angles;
– Night vision with green or black background, such as aviation panels, bedside alarm clock, etc.
Of course, we can always use the LED backlight on the LCD module with fewer LED chips, and turn off the LED backlight when not in use to save power. When transflective polarizer can also be added to some LCD negatives to make it readable in sunlight, but the contrast will be compromised.
The concept of positive and negative mode is not only limited to monochrome LCD Displays (LCD Panels, Character LCDs, Graphic LCDs, etc.), it is also used for color displays or even other display technologies. We will classify the screens as follows,
Positive samples:
– LCD TN positive
– HTN LCD screens
– Yellow and green STN LCD displays
– Gray STN LCD screens
– LCD FSTN positive
Negative screens:
– Negative TN LCD
– Blue STN LCD displays
– FSTN negative LCD displays (STN with film compensation)
– VTN (Vertical Alignment or VA) LCD displays
– FFSTN LCD screens (FSTN double film)
– TFT (Thin Film Transistor) LCD displays
– IPS LCD screens (In-Plane-Switching)
– AFFS (Advanced Edge Field Switching) LCD displays
– OLED displays including PMOLED (Passive Matrix Organic Light Emitting Diode) and AMOLED (Active Matrix Organic Light Emitting Diode)
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