We bought some 12v LED lamps off the internet. In the stables we have used interior strip lights, the ones that look like fluorescent tubes but are actually lots of LEDs, they work really well . Just make sure they are 12v and not 240v!
We run about 10 separate LED lights from 12v batteries varying from 10w up to 30w. They have transfored our yard. They are all switched from normal waterproof light switches so it looks and feels like a proper lighting installation, but is all 12v.
These are some of the small ones, we use one in each stable, and others dotted around.