Here’s an idea, why not go old-fashioned and put an industrial grade, lamp post in the middle of your backyard. That would work. With a 250 watt mercury arc lamp, lighting up the backyard, and the rooms facing the backyard, as well as your neighbor’s houses. Unfortunately, that is not neighborly, nor is it energy efficient and good for the eyes.
It all goes back to why you would want a backyard decorated. You want it to be a place where you can be mellow over a six-pack (or two) with friends and families. A mercury-arc lamp will just force you to wear sunglasses at night, which is not cool, mellow nor beer-friendly.
Soft lighting is easily achieved in a variety of ways, at a more affordable cost. You could have malibu lamps, situated around the backyard, or some form of accent lights all across the space. The important thing is that you don’t need to have a big blinding spotlight out back.
You can have some peace and relaxation, and easy entertaining space for your family and friends with the right lighting.