I have run light boards on many occasions, both ones that are programmed and also one with just faders to push up and down (that was the show where I was the only person in the booth and ran the light board and then also sound and video from a laptop). I know how to skip to a certain cue and also back up a cue, and turn the board off and on. Where I start to get on shaky ground is the whole hang/focus/program the board part.
Lighting design was offered as a course in my theatre program in college, but I didn't take it because they had drafting as a prereq and a) I hate math and b) I was double-majoring and not taking summer school, so everything had to count for credit and the drafting class wouldn't have counted for anything, I just had to take it before I could take lighting design. So I didn't.
I did do a lighting design for a production of The Glass Menagerie when I was working outdoor theatre summer stock in 2004 or thereabouts. We had our own black box and the cast and crew of the outdoor drama did their own shows throughout the summer, just for us. I had heavy assistance from another technician who actually knew lighting design (he helped me hang, focus, program etc). So I know the bones of the process but really would be lost without help.
I just think that in my region, LDs are more consistently paid vs. stage managers (I have pretty much stopped SMing for one theatre because they do not pay stage managers while they do pay directors, designers, etc), and the time committment is way shorter and therefore equals more work (assuming anyone would want to hire me). I think I will think on this some more and then see if any of my LD friends would let me assist on their next project....
I found the exact opposite. I am primarily an LD but have forayed into stage management because of more regular jobs and payment. At least around my parts no one seems to think about an LD until halfway through rehearsals which by that time I am booked for SM shows for the next 6 months. A lot of times people just assume that the house tech can make something work with the house plot.
Although I think lighting design is a great field it takes a lot of work whereever you happen to be as it is a field where, unless you have visualization software, you cannot see your design and whether or not it works until it is too late to change it. I would say just pay attention to any plots you see as an SM and keep it in mind while watching the show so you can get an idea of how fixtures, colours, form, and movement contribute to a look. After a while try predicting from a plot or magic sheet the looks, once that gets comfortable I would say go for it!