Infrared thermography as evaluation method of a faulty status of a LED LCD TV

The paper presents the application of infrared thermography in the detection of anomalies (hotspots) that may lead to defects of the backlight unit, which are not yet noticeable in the visible part of the electromagnetic spectrum. It is shown on a practical example of an LED LCD TV how hotspots at the maximum level of brightness led to the failure of one element of the LED backlight segments in 2 years time. Once the faulty element was detected, brightness was reduced in order to preserve the remaining LED elements. Infrared thermographic analysis of the faulty state was repeated and compared with measurements of photometric values. The thermal analysis results, before and after failure, are displayed in line at the area of the LED elements and in 3D on the screen surface. The photometric analysis was done on the full‐screen area in each of the RGB channels and then followed with in‐detail measurements on 200 points. As most photons emitted from the diode are dispersed to the sides of the display due to the lens mounted on top of each LED and other optical elements, data obtained by photometric means are not as precise in the positioning of faulty LEDs, as ones obtained by thermal inspection. LED LCD TV display failures usually originate from thermal influence at the backlight unit level. Photometric tests do not reflect the accurate state of the backlight unit because of the characteristics of optical elements. Infrared thermography is a nondestructive method that detects radiated heat, which is not affected by optics and therefore allows for precise locating of the malfunctioning segment.