LCD viewing angle: a definition
The view direction is the correct direction marked with Φ which is relative to the X axis. The original location is the center point of the display panel surface, the Z axis is Normal, the X axis is Horizontal, and the Y axis is is Upright.
Normally 4 angles were defined to correspond to 3, 12, 9 and 6 o’clock respectively. So you can find the 6 o’clock or 12 o’clock parameter in the LCD datasheet.
The viewing angle is the angle with respect to the Z axis in a given direction and marked by θ (θ U means upper viewing angle). LCD viewing angle describes the maximum viewing angle and is one of the key indicators of the display module.
The viewing angle can also be explained in the simplest way as shown below.
The LCD screen‘s bias angle is the perpendicular angle from which the screen is best viewed. (See Fig. 2) This angle is determined when the screen is designed and can be set to any angle or orientation. The orientation of the angle of polarization of LCD Displays is often indicated with reference to the face of a watch. If the scroll is above the screen, it is called 12:00 or Top View.
LCD screen display direction: how to set it correctly?
The viewing angle of the LCD screen is the angle formed on either side of the angle of polarization, where the contrast of the screen is still considered acceptable. Typically, this contrast is specified as 2:1 for monochrome LCDs and 10:1 for color LCDs.
A typical STN character display operating with a 1/16 duty cycle has a viewing angle of ±20 degrees and a polarization angle of 25 degrees.
For example, suppose the display is of the type 12:00 (top view). When the screen is viewed from 25 degrees above vertical, it will have the highest contrast and best appearance. If the viewer moves their eyes up the screen an additional 30 degrees, they will see a reduction in contrast, but the screen will still be readable. Moving the view position higher up the screen will reduce the contrast to an unacceptable degree.
Normally, we have the following ways to improve the viewing angle.
How to improve the viewing angle of the LCD screen?
Voltage adjustment to optimize contrast
Adjusting the contrast voltage, V L , affects the angle of polarization to some extent, but not the angle of view. A 12:00 top view can be optimized for a 6:00 bottom view by adjusting the contrast voltage. A 12:00 display set for a 6:00 display position will not have as great a contrast as a 6:00 display set for a 6:00 display position and vice versa.
In general, the screens are optimized for direct viewing. A 6:00 or 12:00 module can be used, and the contrast voltage can be adjusted slightly to optimize the display for that viewing position. In the example above, the display angles of the 6:00 and 12:00 modules actually overlap the perpendicular (or straight) display position.
contrast adjustment
When the view position is set, the contrast setting can be determined. This is done during product development in the prototyping units.
Typically, a 10K ohm pot is connected between V DD and V SS on a single supply module, or from V DD to the negative rail on a dual supply module. The pot wiper is connected to the V. L input of the module. (See Fig. 3)
The LCD screen is moved to the nominal display position and the potentiometer is adjusted to obtain the desired appearance of the LCD screen. The voltage across the V L pin is now measured and a pair of resistors are chosen to produce this voltage in output units.
Adjusting the driving voltage and contrast is the most cost-effective way to improve the viewing angle. Different viewing angles need different driving voltages. It is compromising. When discussing the best viewing angle, we first need to fix the voltage angle.
Change the layout of the LCD screen
– If possible, try to make the driving multiplex (duty ratio) as small as possible. The static unit has the best contrast.
Use a better polarizer
– The higher the efficiency, the better the contrast. It is especially important for negative visualization. Switching from 98% to 99.9% polarizer will do the job.
– In ambient light, the more reflective the polarizer, the better the contrast.
– With backlight, the more transmissive the polarizer, the better the contrast.
Choosing the right liquid crystal material
– The better K33/K11, the better tilt of V90/V10, the better contrast.
– The higher the voltage, the better K33/K11, better contrast (when V10 ≤ 2 volts)
Application of the first quality orientation layer (polyimide)
– Use high quality polyimide (Nissan Chemical)
– Use high quality rubbing fiber and good quality rubbing equipment so that the molecular alignment of the liquid crystal is uniform.
Change display mode
– LCD positive to LCD negative (when LCD is used indoors or in a dark environment, the contrast will increase a lot, but it won’t look good in ambient light alone, it’s also more expensive)
– TN (Twisted Nematic) to VTN (Vertical Alignment)
– Normal VTN (Vertical Alignment) to Wide Viewing Angle VTN .
– TN (Twisted Nematic) to STN (Super Twisted Nematic)
– STN (Super Twisted Nematic) to FSTN (Film Super Twisted Nematic)
– Blue STN (Super Twisted Nematic) to negative FSTN (Film Super Twisted Nematic)
– Negative FSTN (Film Super Twisted Nematic) to FFSTN (Double Film Super Twisted Nematic)
– Normal FFSTN (Super Twisted Nematic Double Film) at Wide viewing angle FFSTN
– Negative FSTN (Film Super Twisted Nematic) to ASTN (Automotive Super Twisted Nematic) (especially when temperature changes).
– FFSTN (Double Film Super Twisted Nematic) to TFT (Thin Film Transistor)
– TN (Twisted Pneumatic) TFT to IPS (In-Plane Switching) TFT
For TN display, when multiplex is 4, some customers complain that direct display is not clear (perpendicular to LCD). The solutions are:
– Change LCD from TN to HTN, 95% customers will be satisfied with HTN LCD.
– Redesign the LCD screen to make it 3 multiplex or even lower multiplex.
When an LCD screen is high density with segments/icons or very crowded, some customers also complain that the viewing angle or contrast is not good. The reason is that the screen is cluttered, the design can be long and thin. The voltage drop across the design can be large. The solutions are:
– Use low resistivity ITO glass to reduce design resistance.
– Use STN or even FSTN to increase viewing angle/contrast tolerance.
Do you want to know more about LCD, OLED and TFT solutions? – Consult our knowledge base, where you can find advice on operating temperature of electronics and the differences between LCD and TFT !
