Maybe you had seen picture as above in any LCD (Liquid Crystal Display) datasheet. Do you know what it means?
It indicate View Direction and View Angle parameter of LCD in one picture.
View Direction is the observation direction marked with Φ on the display panel surface . Normally we name Φ=90° as 12’ o’clock and Φ=270° as 6’ o’clock just like watch.
View Angle is the angle refer to Z axis marked by θ. View Angle indicate the maximum angle on View Direction
Why does LCD have View Direction and View Angle?
Phase delay Transmission
The phase delay and transmission are different when the light pass through the Liquid Cristal from different direction.
A direction is brighter because it has max phase delay and max transmission. But C direction is almost dark. So you can define A direction as View Direction and angle of B and C as View Angle.
In fact the View Angle definition is not so simple because of the Liquid Crystal nonuniformity and different judgement you chosen such as contrast or gray scale inversion .
What View Direction and View Angle do we need?
View Direction can determine the best view direction and avoid putting the display at wrong place.
Off cause the big View Angle is better ,It is means that you can see perfect image by large inclined angle without any distortion.
Here we just introduce a simple concept and want to help for your LCD choice .