Contrast Ratios of Displays
Figure 1: Microspectrometers are used to measure the contrast ratio of each pixel
Figure 2: Typical test spectra from a display. Intensities can be directly compared between pixels.
The contrast ratio of individual pixels and microdisplays can be measured and compared using microspectrometers.
Flat panel displays consist of a series of colored lighted areas arranged in a pattern and can only be readily viewed with magnifying optics. Due to the high resolution of flat panel displays, they are manufactured with hundreds of rows of microscopic "pixels" on a surface. Generally, these pixels are red, blue and green though pixels with other colors are also made...for example the latest four color systems also incorporate yellow pixels.
One aspect of display quality control consists of making sure that the contrast ratio of each pixel does not vary across the entire display. For example, all the green pixels should have the same contrast ratio no matter where they are positioned in the display.
Microspectrometers are able to gather contrast ratio data from single pixels and from groups of pixels (if you are interested in mura). Additionally, microspectrometers are also able to map the relative intensity variation within even a single pixel! This leads to a new level of precision for improved displays.
The way a microspectrometer works is that spectrophotometer entrance aperture is placed over the pixel or pixels in questions. The black square in Figure 1 is an example. The spectra is then acquired and will look something like the three spectra in Figure 2. Using the Lambdafire™ software, the intensity data is compared with measurements of other pixels to show that the brightness of each sampled area is within the manufacturing parameters. A high resolution map of the relative intensities can then be generated.
Learn more about microscopic contrast ratio measurements of displays below: