Shown on this page is a chart comparing the brightness, color coverage, and power consumption requirements of two Sony LED/LCD TVs that incorporate Quantum Dots with the first generation OLED TVs released by Samsung and LG.
Without getting into a lot of technical detail, when you compare all four sets, you find that color coverage the two Sony Quantum Dot (QD Vision) -equipped LED/LCD sets and Samsung OLED set are very close, while the LG OLED set actually appears to under perform.
On other hand, while the Samsung set is capable of high brightness output, both the Sony QD Vision LED/LCD and LG OLED sets are very close.
However, the most telling difference is in power consumption. As you can see, both the OLED TVs consume more power than either Sony set, especially when you further consider that the 65-inch Sony 4K set consumes less power than either 55-inch OLED TV. This would mean, barring any engineering advances in future generations of OLED TVs, that a 65-inch OLED TV may consume more power than its QD Vision LED/LCD TV equivalent.
Also, another thing to keep in mind is that while LED/LCD TVs consume power on more steady level regardless of brightness output (although other features on the TV, such as Smart TV, etc..., when engaged can affect power consumption), OLED TV power consumption changes with the level of brightness required to produce images. So, the brighter the content, the more power that is consumed - and of course, engaging Smart TV and other features will also change this as well.
So, as you can see as shown in the chart, the extra cost factor in both manufacturing and purchasing an OLED TV may not deliver that much of an improvement over a Quantum Dot-equipped LED/LCD TV.