Manufacturers of LCD backlights based on LED, CCFL (cold cathode fluorescent) and flat lamp sources must control quite a number of different device output parameters in order to meet customer demands. Typically this involves identifying Mura defects and particulate contaminants, and measuring brightness, brightness uniformity, and correlated color temperature (CCT). For LED backlights, color and color uniformity are also important, especially for LED backlights. Some of these measurements may even have to be performed as a function of view angle.

Human visual inspection, which has been the standard for the backlight industry, cannot keep pace with manufacturer’s needs as both production quantities and the physical size of displays increase. Radiant Imaging has developed an array of products specifically matched to requirements of backlight producers, as well as to support development efforts.

Our PM Series™ Imaging Photometers and Colorimeters are highly accurate systems useful for making precise spatial measurements of luminance and chrominance. They deliver automated access to a wide range of display test and analysis capabilities, including brightness and color uniformity, chromaticity coordinate information, color temperature, angular dependence of display properties, as well as Mura and particulate defect detection. Built-in support for ActiveX controls allows the experienced user to develop customized applications, and to perform automated testing using software such as LabView, Matlab, VBA, VBScript, Javascript, C and C++.

The Radiant Imaging PM-FPMS™ enables uniformity measurements as a function of viewing angle for backlights of up to 1.7 m x 1 m in size, and is intended primarily for display development. This system includes an automated goniometric motion system and system control, data acquisition and image processing software. The PM-FPMS™ can produce qualitative backlight images, as well as an extensive variety of quantitative plots, such as isoplots, CIE color analyses and radar plots (color or brightness as a function of view angle), for any sampling area size and view angle. These measurements are automatically corrected to simulate viewing all points on the display from the same angle.

The Radiant Imaging IS-VA™ utilizes unique, patented Imaging Sphere™ technology to perform high-speed measurements of backlight color, luminance (brightness) and contrast as a function of view angle. The IS-VA™ provides a lower cost alternative to traditional conoscopes while still delivering excellent performance, flexibility, and reliability. The IS-VA™ is faster and more economical than the PM-FPMS™, however, it has a fixed sampling area size. In contrast, the PM-FPMS™ measures the entire backlight surface at high resolution. The combination of high speed and high resolution makes the IS-VA™ ideal for both R&D projects as well as real-time production QC tasks.