What They Say
A hat-tip to Dave Haynes of Sixteen:Nine.net for sending me an interesting collection of images of LG digital signs which seem to be very blue (see a few of the images below). This confused me as it was much more extreme than a ‘blue filter’ kind of issue. (it might have just been a setting problem). It got me digging around the net and I found plenty to support that there has been a problem with this issue in consumer TVs (although a fair proportion of the reports were from 2019).
I was slightly baffled as the backlights have blue LEDs that drive YAG (yellow) phosphor that converts some of the blue to green and red. I had not heard of YAG failing in white LEDs, but then I found this recent YouTube video (the link opens the video at the most interesting part). A repairer shows that some of the LEDs have changed from white to blue and it is clear that the YAG layer has failed (or disappeared). I captured a couple of still images from his video that show this. He describes this as a ‘very common problem with LG TVs’ (although I have also seen references to issues with Samsung and Vestel sets, as well).
What We Think
This looks like a bit of bad engineering by LG Electronics or their LED suppliers. I suspect that this issue is a result of driving the LEDs at too high a brightness, which would cause the temperature to rise too much, causing the phosphor to degrade. However, I’d be very pleased from anybody that has a better explanation! I suspect that while consumers would very rapidly get fed up with wrong colours, in digital signage and sports bar applications, staff are less picky, as long as there is an image. (BR)
These captured images from the video show the disappearance of the YAG phosphor from some of the LEDs
