LED displays
Viewing angle: how widely a screen spreads its light
An LED shines brightest straight ahead. From the side the screen looks darker. How wide that bright zone is, the viewing angle, you largely determine with the lens and the choice of LED.
Stand at an angle in front of a screen, right off to the side. The image then often looks darker than when you stand straight in front of it. That is because of the viewing angle.
Some screens send their light out in a narrow beam straight ahead (good when the viewers are far away and right in front). Others spread their light out widely (good when many people are looking from all directions).
The viewing angle is the angle that defines an LED’s region of maximum brightness. Beyond it the brightness drops sharply, typically to about 50% of the maximum. It is in fact a three-dimensional cone in front of the LED, with a horizontal and a vertical component.
Narrow or wide
Common viewing angles are 30° (narrow and bright, for an audience that is far away and straight in front, e.g. along a motorway) and 70° (wide, for a broad audience). With SMD LEDs, where the chips sit at the surface, much wider angles are possible (up to about 160°), which makes them suitable for indoor screens where people look from the side.
The trade-off with brightness
For the same power: the narrower the beam, the more light straight ahead (higher nits on the axis), but the faster the image fades to the side. A wide angle distributes the light over more directions. The right choice therefore depends on where your audience stands.
The viewing angle is conventionally defined at the point where the luminance has dropped to 50% of the on-axis value (half-power angle, FWHM). Horizontal and vertical viewing angles can differ, depending on lens and package. DIP LEDs with a lens generally have a narrower, strongly directional beam; SMD packages spread more widely.
Luminous-intensity budget
The total luminous flux is finite; a narrower viewing angle concentrates it into a smaller solid angle and thus yields a higher on-axis luminous intensity and luminance for the same power. That is favourable for legibility at long range straight ahead, but unfavourable for broad audiences. The viewing angle is therefore a design parameter you choose together with the required nits and the geometry of the location.