In one of his loveliest song lyrics, Shakespeare asks, "Who is Silvia?" The other morning I asked Judith Light, "Who is Silda?" Silda Grauman is the character that Light plays in "Other Desert Cities," and Light responded: "Within the body of the play it seems that she is the truth teller, and the heart of the political left. She is a very complex person who uses her humor to cover over the depth of sadness and despair she has always felt in relation to the sister that she loves so much." 

With a description that concise, I thought: what more is there to say? But just as Light and her "Other Desert Cities" colleagues have continued to mine the play's text every night for months, so did Light, in our interview, keep excavating her character. 

"Silda has taken herself down by her addiction to alcohol," Light said. "It's not specified as such in the play, but her addiction has gone on for many years." Did she research this aspect of the character? "Yes. When you have a play as brilliant as this one, and a writer as brilliant as Robbie Baitz, you have to do your homework." Light spent time at St. Luke's-Roosevelt Hospital in midtown Manhattan, working with Paul Rinaldi, the Clinical Director of the Addiction Institute. "He is a wonderful man, and I got a lot of useful information." 

Silda isn't all sorrow and Seconal. She also detonates some of the play's biggest laughs. How does Light approach that aspect of the character? "It's essential," she answered, "that even as you know you're funny that you play the truth of the moment." Light added that Silda's humor "is part of her drive to make sure that she's not overlooked - that she's not taken for granted. In many ways, she has lived in the shadow of this family. It's her truth-telling that makes her funny. And my job is to find the balance between the humor and the sorrow." 

How does Light keep herself in shape to make good on that nightly challenge? "I have to take care of myself and my health," she replied. "I have to meditate. I have to do yoga. I have to eat properly." 

Light revealed more about her daily routine. "I always walk to the theater no matter what the weather, because I go over the play in my head as I go to the theater. That way, I'm already in the play by the time I get there." 

Because Light feels a responsibility toward all the people who help support the cast nightly backstage at the Booth, as well as a "tremendous responsibility" to the play's audience, she says that she tries to dial down some of her social commitments while she's doing a play. Still, she finds time for the commitments close to her heart. These involve, in particular, her commitment to working with young performers and to helping organizations in the field of HIV/AIDS and in LGBT issues: to human rights in the largest sense. 

As my conversation with Light wound down, I asked her why, after a career in which she has been known to millions for TV shows like "Who's The Boss?" and "Ugly Betty," she has done back-to-back dramas on Broadway: before Silda, she played the title character's wife in "Lombardi," for which she received a Tony nomination. 

"I didn't say to myself two years ago, 'I'll do theater now,' even though it's where my career started. I had that longing, however, in my heart. And I'm very fortunate that things have turned out as they have. I find that when you give up the idea of trying to control everything is when a lot of the best things in your life tend to show up." 

Brendan Lemon is the American theater critic for the Financial Times and the editor of lemonwade.com.