Canofworms - I have to run & will reply this aft or tomorrow, but for now will post something I copied... in case it helps another newbie like me: http://www.thisoldhouse.com/toh/article/0,,403815,00.html (A Lesson in Bathroom Lighting); excerpts: "Task Lighting Vanity lighting gets top consideration because these fixtures work the hardest to illuminate the head and face for grooming. The most common mistake people make is putting recessed ceiling fixtures directly over the mirror. These cast shadows on the face, making daily grooming rituals more difficult. Vertical fixtures or sconces mounted on either side of the mirror are best for casting an even light across the face. But given the size and positioning of some vanity mirrors, sidelights can be impractical (mounting them directly to the mirror is always an option, but at greater planning and cost). Only then do I suggest a fixture for over the mirror. It should be placed 75 to 80 inches above the floor and, like all vanity lighting, contain at least 150 watts ÂEideally spread over a fixture that's at least 24 inches long so that the light will wash evenly over the hair and face. The shower is a secondary area of task lighting. In smaller bathrooms, if the stall has a clear glass door, a dedicated fixture may not be necessary. Otherwise, I recommend a recessed light with a glass lens (plastic will yellow). Similar recessed fixtures work well over a freestanding tub or the toilet. " "Lighting the Vanity Right To eliminate shadows under the chin, eyes, and cheeks, fixtures should be mounted on either side of the vanity mirror (or on the mirror's surface, if it's large), 36 to 40 inches apart. The center of each fixture should be roughly at eye level, or about 66 inches above the floor. This will guarantee even illumination across the face for grooming...." "Choosing Bulbs A crisp white light tends to render skin tones most accurately. Halogen bulbs set the gold standard...." "Think Dimmers These are a lighting designer's best friend because they grant absolute control over the lighting, and thus the mood, of the room. In a very small space like a powder room, dimming the vanity fixtures might even provide all-in-one task, ambient, and accent lighting. Plus, dimmers conserve energy...." Here is a link that might be useful: A Lesson in Lighting - This Old House

Personally, I would opt for the 20"W x 31"H recessed. I prefer recessed medicine cabinets or flat mirrors. I think 20x30 would look fine with a 30" wide vanity. It won't be square like your inspiration picture, but rectangle looks good too. I have two rectangular pivot mirrors in two different bathrooms, one is proportionally narrower than the other and I like both.

I am looking at the same RH cartwright as well. I would definately do the small for a 36" vanity. I'm doing a small for my son's bath and his vanity is 48". Part of it depends on how you will do your lights- scones to the side of the cabinet or fixture above. We are starting framing next week. The joists and subfloor on the first floor are in. FYI, RH will have a bath sale shortly after christmas and I plan to purchase the cabinets then. I'm trying to decide which size to do in the master. We have 2 vanites and each will be about 54-57". The big one sounds enormous, or maybe it feels wrong for that style of cabinet. Any opinions? Here is a link that might be useful: RH cartwright medicine cabinet

For size, you can also get customized sizing where cabinets can be ganged together. For example, two 12 inch cabinets ganged together or two 15" ganged together would work where you can add lighting as an option and have interchangeable left or right open doors. It gives you alot of storage over your vanity without looking too wide. And if you want to spend the extra cost, you can have them recessed mounted as well. This will make them look flush with wall and less bulky over any sized vanity. And some of these mirrored medicine cabinets have integrated LED lighting, which can also offer a nightlight with dinner function. So, you will not only have lighting from your main bathroom, but an additional light source. I hope this helps