Originally Posted by rogo
Darin (good to hear from you) and TGM, good points from both of you. I basically agree across the board.
Fundamentally, my sense is that the white serves a pretty limited function. And I think TGM, you agree here, too. Getting back some lost output more than trying to "save the pixels from themselves".
I doubt very much the long-run plan is to keep using the white for this reason. The design gets a lot simpler over time without it and given that you can lose the corresponding transistors, you probably don't need much improvement in overall light output to justify dropping it (if you're overall goal is a power budget).
Of course, to the extent that driving the material harder has some effect on lifespan, that's also a concern. But it seems probable that, too, will be mitigated over time.
One other random thought. LG uses a color-filter design that is not a million miles removed from their LCD technology because they're exceptionally good at patterning and producing that layer. The OLED makes light really differently from LCDs, however. It might make sense over time to rethink the color-filter layer and/or add a special film in between the light and the CF. Some sort of purpose-built OLED BEF (brightness enhancer) that takes advantage of the way OLED works. It looks like a lot of potential light is lost to the rigid lines of the color filter and/or the electrodes. That seems like an area where long-term improvement is more than a hypothetical.
I'm just not understanding why you are saying this (in bold above) - do you have some other specific information or are you just commenting on the same examples that have been posted.
Extracting the 'grey component' (or 'common mode' if you are EE like sooke and I) is a pretty important function and leads to significantly less use of the primaries (especially blue).
And since the examples shown never show all three primaries lit up, it's pretty strong evidence that this is exactly how the white sub is used (as pointed out by TGM).
When there is no grey component, the white sub must be off by definition (including the case of any two of the primaries being used all the way up to 100%).
But let's consider the color composed of 100% R + 100% G + 100% B (ie: a white).
Let's assume the color filters are 50% efficient and further that the light output fro the WOLED layer is evenly divided 33% into each primary (as far as the color filters are concerned).
So each of the colored subs is only going to be ~17% efficient and driving the R & G & B primaries at 100% is only going to result in light output which is ~17% of that produced or ~50% of the light output of a single sub.
That means if the white sub pixel is going to be used to drive that same white light output, it only needs to be driven to the 50% level (because none of the primaries are filtered out and there is no color filter to further degrade efficiency.
Both for reduced power consumption as well as increased lifetime, I would think LG would want to make use of the white sub whenever possible and as strongly as possible (meaning to the limit offered by the grey component).
We can debate this ad nauseum, but the easiest thing would be to convince an owner to run color ramps or a color palette and check with a magnifying glass for any examples where all 4 subs are used. My guess is that there are none (with the possible exception of the brightest possible white which would be ~150% of what the white sub could put out all by itself driven to max).
By way of comparison, if LG sacrifices the white sub and increased the size of the other primary subs (to 133% of the current size), max white output would increase from ~50% of the current white sub to ~67%.
To me, a white subpixel makes a heck of a lot more sense than a yellow subpixel (as in Sharp) and I won't be at all surprised to see it hanging around for a long while.
All of this analysis glosses over the impact of the inter-subpixel spacing which would make the 'eliminate the white sub' scenario a bit more favorable (but not enough to change the overall message).