Luminance Measurements of Displays
Figure 1: Microspectrometers are used to measure the intensity of each pixel
Figure 2: Typical test spectra from a display. Intensities can be directly compared between pixels.
The luminance, intensity or brightness of individual pixels and groups of pixels 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 brightness or luminance of each pixel does not vary across the entire display. For example, all the green pixels should have the same brightness no matter where they are positioned in the display.
Microspectrometers are able to gather relative intensity 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 luminance measurements of displays below: