Here's what I found at:
<http://www.royalcaribbean.com/findacruise/experiencetypes/experiencetype/experience/home.do;jsessionid=0000neVt0Jqf0Tfr7MzsqlAleZ7:v29bc620?br=R&exCode=23&shipCode=LG>
Dress Suggestion
During the day, casual clothes are fine for the main dining room. In the evening, there are three distinct types of dress onboard: casual, smart casual and formal. 3 to 4-night cruises include one formal night and two or three casual nights.
7-night cruises include two formal nights, one smart casual night and four casual nights.
10, 11, and 12-night cruises include three formal nights and three smart casual nights; all other nights are casual.
14 and 15-night cruises include three formal nights and four smart casual nights. All other nights are casual.
Suggested guidelines for these nights are:
Casual: Sport shirts and slacks for men, sundresses or pants for women
Smart Casual: Jackets and ties for men, dresses or pantsuits for women
Formal: Suits and ties or tuxedos for men, cocktail dresses for women
Bare feet or bathing suits are not allowed at any time in the dining room and shorts are not permitted at dinner. Each ship also offers a variety of casual dining options, for example, the Windjammer Café.
Hope this helps