Defining Distance: Pixel Pitch vs. Fill Ratio
If you are at all familiar with digital displays, you know that they are composed of hundreds, thousands, and sometimes millions of small, individual pixels. While the number of these pixels determines the resolution of the display, the spaces between pixels can actually have an equally large impact on the picture quality the display creates. There are two ways to measure the space between pixels and each tell their own story. The first is pixel pitch, a common specification listed early in the description of any digital display product. The second is fill ratio, the less common of the two metrics and one that only you’ll find listed much lower on any given spec sheet. Understanding the difference between these two specifications is crucial to identifying which display is best for your needs.
Pixel pitch measures distance between centers of adjacent pixels
In straightforward terms, pixel pitch and its analogs, dot pitch, line pitch, P(x), and strip pitch are metrics used to communicate the distance between the centers of adjacent pixels. More specifically, pixel pitch indicates the straight-line vertical or horizontal distance between the centers of discrete LED pixels each composed of a red, green, and blue diode and aligned within a grid. Think of it this way: if you are standing a set distance next to your friend, your pixel pitch (or person pitch, in this case) would be the distance between your heart and your friend’s heart. Height and width do not factor in at all, all that’s measured is the distance from center to center.
When discussing flat panel or curved display panels, where the display is either a light-reflecting or light-emitting technology, pixel pitch is measured on the surface of the screen or display. With projection technology, it is measured at the projection source rather than the destination screen. That being said, you probably won’t encounter the term pixel pitch unless you are working with direct-view LED. LCD, LED back-lit LCD, and any projection technologies are much more likely to define image quality using resolution.
As pixel pitch shrinks, the closer together the distinct elements of a digital image become. That will make the image itself appear more cohesive. Today’s most narrow LED pixel pitches are around 0.9 millimeters for a traditional LED diode, though emerging mini- and MicroLED technology is attempting to shrink these pitches down to 0.10 millimeters.
Fill ratio measures empty space between pixels
Often confused with pixel pitch, which is the distance between the centers of adjacent pixels, fill ratio instead measures the blank space between the closest edges of adjacent pixels. The fill ratio, or more scientifically, the comparison of the amount of active pixel package surface area to the inactive, is calculated by taking the area of the front surface (length x height) of the pixel package size over the square of the pixel pitch. So for example, if we have a 4.7mm pixel pitch display constructed using standard 3030 SMD LED packages (3.0mm height by 3.0mm length), the formula would read:
A lower fill rate can make the pixel pitch seem smaller without actually changing it. A higher fill rate on the other hand can make the pitch seem wider but it facilitates a better contrast ratio because there’s more black visible against which the pixels can stand out. Lower fill rates often correspond with larger pixels, all else equal, and the larger a pixel is the more expensive it will be.
As consumers move along the process of acquiring a digital display, they would be wise to familiarize themselves with the various specifications that will govern their future product. Pixel pitch and fill ratio are two of the most fundamental specifications to grasp but there are countless others that carry similar importance. If you’d like to explore what those specs are, we encourage you to download our latest white paper, Hey! What Does This Spec Mean? and to register for the webinar expanding upon that paper, entitled Locking Down LED Lingo.