Our lighthouse was occupied from 1853 to 1964, but of course visitors get more excited by the earlier time periods.
See The Keepers slide show. We do not have images of all the keepers, but this can give you an idea of what they wore. Of course there were more male keepers and assistants than female.
Women generally wore conservative, professional clothing from the time period they served. Men, until the later times, wore a uniform (1884 - present) of some sort. Of course, you need not appear as a keeper. I have made a 19th century photographers outfit and visitors respond well to that.
A period costume shows you care about the history of the lighthouse and presenting a good image to visitors.
My own experience and those of others has been very positive. See image from our 165th birthday celebration:
Local: Reincarnation 214 17th St. Pacific Grove, CA
On line: Historical Emporium 19th and early 20th century clothing/accessories for men and women. Great selection. Not cheap.
Ideas: A24 - as seen in the movies. Lots of different looks, including the oil skin.
Historical Sewing
Historical Sewing - Gentleman
Men's Clothing Pattern for the 19 Century
Amazon Drygoods
Timeless Stitches
Reconstructing History
This is one area where the ladies have it easier than the gentlemen. In times past dress was much more conservative. No ankles, necks or bare arms (gloves are a nice touch even). You can likely put together an outfit from whatever you already have. An ankle length skirt, a full sleeve blouse, shawl, hat (ladies ALWAYS wore hats) and gloves if you have them. Shoes will give you away, only if they show.
We have it harder, depending on how you want to appear. You don't have to be a keeper. Day labourers might wear jeans, a full sweater, leather shoes or boots. For the posh it gets harder. West Coast wore derbies, east coast wore top hats. (sorry no baseball caps). White shirts, dark dress pants, a vest, a tie of course, a dark dress coat and nice leather shoes. Think British gentleman.
ANY effort shown will be noticed and appreciated. Coming in casual, work in the garden clothes, says you don't care to even look professional. Obviously, no shorts, sandals, etc.