Dot Pitch – also called Phosphor Pitch or Line Pitch – refers to the distance between the sub-pixels (phosphor dots) or liquid crystal display cells of the same color inside a display screen. Expressed in millimeters, technically, dot pitch is the sum of the size of a triad and the distance between the triads (a triad is a cluster of three phosphor dots, colored Red, Green, and Blue inside a CRT screen).
A smaller dot pitch means a smaller distance between the phosphor dots and hence better image clarity. Unfortunately, this is not always an accurate method of comparing different displays, for a number of reasons:
- The dot pitch is measured in a number of ways by different display manufacturers
- Differing pixel geometries make it difficult to reach a conclusion linking the dot pitch and image clarity
- Different screen resolutions make the process of judging picture quality a difficult task
- The tightness of the electron ray aim and focus will vary between displays
Dot Pitch Measurements
Traditionally, dot pitch has been measured diagonally and this technique is widely assumed to give a more accurate representation of the monitor. In the mid-90s, in order to exploit the common assumption that a lesser dot pitch means better clarity of image, some manufacturers started using horizontal dot pitch measurements as a marketing ploy. Measurement of horizontal dot pitch alone – by completely eliminating the diagonal measurement – will yield a smaller value for dot pitch, and by doing so even a low quality monitor could get impressive looking dot pitch values. Some customers were fooled by this tactic, but as awareness spread, buyers started to become more vigilant in their quality check.
The exact difference between diagonal and horizontal dot pitch depends on the architecture of the monitor under consideration. A typical entry level monitor will have a diagonal dot pitch of 0.28 mm while its corresponding horizontal dot pitch will be around 0.24 or 0.25 mm. A monitor with a diagonal dot pitch of 0.26 mm will have a horizontal dot pitch of around 0.22 mm. As mentioned earlier, these dot pitches will vary with manufacturer and design, but in most cases, they will be near to these values. These values are useful for analyzing the dot pitch of a monitor before purchasing.
Some monitor manufacturers quote both the diagonal and horizontal dot pitch. From a smart customer point of view, it can be assumed that if a monitor has only the horizontal dot pitch displayed, it is a low-end product. On the other hand, if it has both the values, then the buyer's job of quality verification is easier.
Aperture Grill Displays
Dot pitch measurements do not apply to aperture grill displays. These displays do not have vertical dot pitch, but only horizontal dot pitch or aperture pitch.