I had UVB phototherapy back in 2010, after struggling with guttate psoriasis for a few years. The phototherapy completely cleared up my guttate psoriasis (and it didn't come back for 4 years after that!) and my inverse psoriasis. It did help my plaque psoriasis but that went back to its pre-phototherapy state fairly quickly. I used the fully-body stand up booth, and went twice a week for around 3 months I think. I started off at 9 seconds which seemed a little ridiculous, especially as I had to drive for 20 minutes each way to have the treatment! I was at university part time, so I was able to take the time twice a week to travel to the hospital. I know for some people this isn't really feasible.
With regards to light treatment at home, I have the same concerns as Vicki - that I might do it wrong or burn myself. But I can completely appreciate how it would be convenient and save time, and perhaps money in the long run.