I use myself both GU10 and MR16 bi-pin (low voltage) LED replacements for what should be Halogen bulbs.
If you need the amount of light that you get now from the 50W bulbs, then no. This will not cut it.
But do you?
I have 6 GU10, 3W each LED that go on a fixture designed for 6 35W Halogen. For dinner, that is all I need. Yes, it is on the romantic side, but since you have 6, you can point 3 at the table and 3 at the walls around and you have both decent task light and ambient light.
Add to that the fact that there is the option (almost always)to add more ambient light (add the 3 LED above the bar next to the dining table, or the 2 wall lights in the hall next to it) and you are just fine.
In my kitchen, I have 12W LED recessed lights which replace 65W equivalent and they give PLENTY of light. you can do brain surgery under that light... So really, people give LED bad rap. They do great job if you get the right light for the right setting and make sure to get the right amount of Lumens.
The W per Lumen ratio is great, and light quality is great. It only fails when people don't realize that the things they buy, even though it should be clear based on the data on the package, are too weak to replace the incandescent bulb. a 3W LED cannot replace a 50W Halogen is the short answer, but LED CAN replace Halogen if you plan it right.
To make sure you get light in the winter, you need a deciduous tree (one that loses its leaves in the winter) planted on the southern side of your home (where the sun's rays are the strongest for people in the northern hemisphere). Pay special attention to the size the tree with grow to when mature, both in height and in width of the canopy. I'd recommend playing it well outside of the canopy's reach from your home to protect not only your siding, but also your foundation from roots that will travel often twice the range of the canopy.
Take special care to check for buried utility lines and place your tree away from any of them. You also want to be sure it is not too close to a sewer line, since the roots have a habit of growing into and clogging sewer pipes.
Finally, realize that a tree will add beauty and natural energy efficiency, but it will also add to the maintenance of your home, particularly from leaves clogging the gutters, and falling branches. If your only goal is energy efficiency, you may be better off upgrading to energy efficient windows and sealing any drafts.
Best Answer
This gets into efficacy/usefulness verses efficiency and the important fact that less voltage is far more stabler.
If you look closely:
Thus the 240V 50W is 3kWh/1000h more efficient in energy consumption.
However the 240V 50W has half the life span of the 12V
Thus the efficiency you would gain is nullified due to the decreased lifespan.
Next compare the luminous intensity
By far the 12V has a much greater efficacy to efficiency ratio.
Now to explain why
Voltage is the rate/speed/pressure of electrical phenomenon.
On average 12 volts is plenty fast to illuminate a 50 Watt incandescent or halogen.
Increasing the voltage beyond this point as you can see does little help as the efficacy "usefulness" of the bulb to achieve desired illumination in relation to the efficient use of energy it requires is most satisfactory at 12 Volts.
As an experiment, take a 9 volt battery and touch the two prongs to a 20 watt halogen MR16 or MR11. The voltage required to reach the desired efficacy is very little, and less voltage/pressure is a good thing.