Are Your Screens Looking Blue? There’s A Reason …

October 27, 2021 by Dave Haynes

Display Daily has an interesting post up (but behind a modest pay wall) about an issue with some flat panel displays that was relayed to me, but was technically kind of over my head.

UK-based Display Daily editor Bob Raikes is very strong technically, so I passed along the photo link, curious about his thoughts. He has posted his point of view on how TVs and maybe commercial panels are taking on this noticeable blue mist or haze:

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).

Bob’s thinking:

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.  

My own thinking:

When you start looking for examples, they are not hard to find. I’m not sure which manufacturer panels were in use, but the blue haze or mist was evident on at least one of the screens in my local Ikea.

Here’s another photo in which you can clearly see the individual LED backlights (the grid of white orbs).