They are mostly nocturnal but they derive their ability to see in the dark from their elven forfathers. They have little red eyes and some even have slits more than anything else. And you are right. The lower orcs had more limited capabilities. The Uruk-Hai could take the sun though they didn't like it. There is a mix of Uruk and Oruk in the picture above. Mostly the Uruk have better weapons and stand more upright and are generally more human. The Oruk are the loincloth-clad ones. Longer arms and more pronounced features. Need to probably play witht he texture more on them. They are a different map for each but it isn't as defined as I thought.