Without getting too technical, the reason likely revolves around power conservation and differences in the way AMOLED and LCD screens utilize energy: In short, AMOLED screens are lit on a pixel-by-pixel basis, so if fewer pixels are active, less power is utilized. LCD displays, on the other hand, rely on a backlight and are affected by total brightness as opposed to individual pixel use.
Regardless of the reason, though, what ultimately counts from a consumer perspective is that Samsung's approach makes a noticeable impact on the user experience. The dimmed state is what Android Wear watches show the majority of the time — and the Gear Live's dimmed state looks pretty bad, especially once you've seen how good that state can look on the G Watch.
The G Watch also outshines the Gear Live when it comes to outdoor visibility, though that difference is far less pronounced. The truth is that even with their brightness settings pumped up high, neither watch is especially easy to see in direct sunlight; be prepared to do a decent amount of wrist-shifting and hand-shadowing when you're outside in glary conditions.
Stamina and performance
We'll make this part easy: Both the LG G Watch and the Samsung Gear Live should get you through a full day without worry. But regardless of which watch you choose, you'll almost certainly need to charge it every single night.
Some folks seem disappointed by the need for a nightly charge, but it really hasn't been an issue for me. I charge my phone every night — so now, I just drop the watch on its charger next to my phone at the same time. Honestly, it'd be harder for me to remember if it were a once-every-three-days sort of affair.
The G Watch has the bigger battery of the two — 400mAh compared to 300mAh on the Gear Live — but all things considered, the differences in stamina between the devices aren't terribly significant. Both watches have consistently been able to get me from morning to night, even with extensive use, and both are always low enough by the end of the day that they would need a recharge in order to last another 24 hours.
As a point of interest (given the issue of Samsung's lower quality dimmed-mode display), I left each watch sitting in its dimmed state for a full 12 hours, starting with a fully charged battery. Without any active use or illumination, the Gear Live lost about 24% of its charge over that time while the G Watch lost about 22%. So Samsung's pixel-reducing approach may have been implemented out of necessity since, even with it in place, the Gear Live appears to lag behind the G Watch in overall efficiency.
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