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| Why do backlight LEDs burn out and go blue? |
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| NiHaoMike:
--- Quote from: Twoflower on November 06, 2021, 10:14:55 am ---Could that be that the TV uses kind of 'remote phosphor'? Some TV-Sets use blue LEDs with a bar contain the phosphor or nano-crystals (most of them contain cadmium!) to transform the blue light to the specific spectra required. If that piece fell off/moved that only the light from the LEDs enters the diffusor of the LCD? --- End quote --- Isn't cadmium restricted by RoHS? --- Quote ---I think RGB LEDs for background illumination is not commonly used anymore. From what I've heard too many problems with the uniformity of the used LEDs (brightness, aging, color...) and too expensive. --- End quote --- There are displays that use a RGB backlight and a monochrome LCD, I'm pretty sure there aren't any direct view TVs using that technology although it works on the same principle as DLP projectors. The one application I heard of for it was a tablet that could operate as a regular color tablet with the backlight on or as an eink like tablet with the backlight off. Probably the main problem is that it requires a very fast LCD to not flicker and the power use of such a fast LCD offsets the savings of not having color filters. |
| Twoflower:
--- Quote from: NiHaoMike on November 06, 2021, 07:52:05 pm ---Isn't cadmium restricted by RoHS? --- End quote --- Yes it is but I think there is/was an exception for the Cd-based quantum dots for TV usage (e.g. https://optics.org/news/7/6/8). --- Quote from: NiHaoMike on November 06, 2021, 07:52:05 pm ---There are displays that use a RGB backlight and a monochrome LCD, I'm pretty sure there aren't any direct view TVs using that technology although it works on the same principle as DLP projectors. The one application I heard of for it was a tablet that could operate as a regular color tablet with the backlight on or as an eink like tablet with the backlight off. Probably the main problem is that it requires a very fast LCD to not flicker and the power use of such a fast LCD offsets the savings of not having color filters. --- End quote --- An interesting technique replacing the filters by time multiplexing. Sounds logical, as it has also an advance in the resolution as only one single pixel is used for the three colors. But probably nothing for me as I seem to sensitive to the rainbow effect on DLP projectors. I remember some very expensive monitors had also RGB backlight with filters. They supposed to have an excellent color space in that time. But the phosphors for LEDs and filters on the LCDs got better to allow the huge color space of modern monitors/TVs. |
| amyk:
Wow. :o That is certainly a lot worse failure than I thought it would be. Even the various generic Chinese COBs I've seen have not failed like that, despite being heavily overdriven - usually the die or the bond wire goes first. Almost looks like they were really trying to save on the phosphor application. |
| james_s:
An easy way to tell if it's the backlight is to look around the back and sides of the panel, almost always there is a gap somewhere that light from the backlight will show through. If that leaking light is blue then the backlight is blue. |
| eti:
--- Quote from: james_s on November 07, 2021, 03:06:22 am ---An easy way to tell if it's the backlight is to look around the back and sides of the panel, almost always there is a gap somewhere that light from the backlight will show through. If that leaking light is blue then the backlight is blue. --- End quote --- yep, and it is. |
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