You keep saying there are a lot other technology that will save power but yet Sharp is the first one that bring out those technology?????????
What?
The weight difference between similar device is important since it is an indication of how big a battery the device has. And hopefully an indication of the efficiency of the panel.
No. It's an indication of how heavy the device is. That's it. If you were weighing the
battery as a rough approximation of capacity, that would at least make sense. But you can't weigh a whole device and draw any conclusions from it. If I drag out an 8 pound laptop and put it next to a 4.5 pound MacBook, it would be insane to conclude that the MacBook must be almost twice as efficient. The two are not meaningfully related.
The battery is about 15-20% lower in capacity on the SHT21 compared to the N7. That, with whatever the final rundown on its battery life is, will tell you exactly how much more efficient the whole tablet is. A large portion of that will be due to the display, but not all of it. Comparing the weights of two totally unrelated devices doesn't tell you
anything meaningful about battery life or display efficiency.
I don't get the assertion that the weight difference between Nexus 2 and SLT21 is not important.
It's not relevant to any comparison because they're not remotely the same device. The reason the Sharp tablet weighs less is not because it has a magically lightweight battery (and even if it did, that would be related to battery chemistry). It's not because it has a battery that's a tiny fraction of the size. It's not because the display backplane weighs less (the whole backplane only weighs about 10g!). It's because it's a totally different tablet with a thousand different design decisions.
The same is true of the iPad mini: it is much larger and yet weighs less than the N7. Why? Because Apple made saving weight a much higher priority than Asus and Google did.
So what exactly do you believe the benefit of IGZO panel for a device like Ipad mini be? Can it save 0.1lb, 0.2lb or 0.5lb in weight?
The benefits are obvious: power efficiency, higher pixel density, and responsiveness, with a less steep battery curve. It reduces, but nowhere near eliminates, the added weight and battery requirements associated with building a "retina" class device.
A retina mini with IGZO still needs a bigger battery than the current model, and barring some revolutionary new battery chemistry, that still means adding significant weight. They might compensate elsewhere for some of this, but this is an inescapable fact no matter how much you try to avoid it.
none of us are display engineer
Again,
you are not a display engineer.
Look like the power saving for the 10.8 inches display is about 1/3. for 5 inch panel, the power saving is about 80%+.
That's panel driving power. For crying out loud, Sharp has already pegged the overall power efficiency boost of IGZO at 25%. There's no need to rehash this ad nauseum with increasingly off-the-wall statements. The ballpark is 25%. Going retina is about 65%. 65 is more than 25. End of story.
I don't know how many other ways there are to say that if your display consumes 10Wh out of a total device envelope of 15, going retina is going to push that up to about 19 out of 24 at best. If you introduce a display technology that curbs that by 25%, that means retina at 14.25Wh out of 19.25. 14.25 is still 42.5% more than 10. 19.25 is still more than 15. It's a lot better than 24Wh, but more is more no matter how you slice it.
that is why we are posting in a msg board and not actually making money in designing the Ipad mini or anything similar. I beg to differ about the weight question. There is the display, the blacklight requirement and the size of battery needed. So the engineer can figure out how much weight saving they can get by using IGZO display alone. The thousand other things that a company can do to save battery power can go on top of the IGZO saving. There is no reason that we cannot try to figure out the panel weight saving individually. 
