Actually the Mars II regular spectrum doesn't include any UVB diodes. IIRC, it's 2 kinds of blues, reds, and whites plus a few infrared diodes.
I think it's good that they don't include UVB. From what I've read, it can damage your plant early on. So unless it has a switch for those diodes on the panel, I wouldn't want to use it.
Someday I would like to supplement my lighting with a source of UVB. All I've really seen in my shallow search on the topic are people using reptile lights for short time periods during the bloom phase. I'm on board with the notion that UV stress triggers the plant to make more/stronger glands, I just don't know what amounts and timings of UV are beneficial without actually harming the plants.
Infrared, on the other hand, is known to be directly tied with the growth pattern a plant experiences.
http://www.cannabisculture.com/articles/4576.html
Not the best reference, but gives a good explanation of how infrared signals a plant to grow in certain ways.
The short version:
If red light = IR light, then less stretch.
If red light < IR light, then more stretch.