Invisible is not a word you would use to describe Radcliffe, who, at age 19, is probably one of the most recognized young actors in the world thanks to a certain boy wizard created by J.K. Rowling.
Even dressed down in jeans, black leather jacket, gray T-shirt and the slightest scruff of a beard (which doesn't nothing to make him look much older than his nearly two decades), Radcliffe draws stares as he strides confidently through an office-building lobby.
Upstairs in a television studio, he expounds on the character of Strang, the pivotal role in Shaffer's play, which tells the tale of why this youth blinds a stable full of horses. Words pour out, youthful in their enthusiasm and surprisingly adult in their perception.
"Alan is not academically bright but he has amazing intellect," Radcliffe continues, adding that though the boy "might be considered slightly simple and gentle ... he has an incredible imagination."
"Equus" was a big hit on Broadway in 1974 with Peter Firth in Radcliffe's role and Anthony Hopkins portraying the psychiatrist who tries to unlock his secret. Hopkins' part is now being played by Richard Griffiths, who co-starred with Radcliffe in the 2007 London production of "Equus" and who portrays nasty Uncle Vernon in all those spectacularly successful "Harry Potter" movies.
Griffiths and Radcliffe are charter members of a mutual admiration society.
Says the older actor, a Tony winner for "The History Boys," of Radcliffe: "I'm really pleased with him. He's right at this awful stage of moving from being a child actor to no longer a child."
And Radcliffe returns the compliment: "To work with Richard on stage and in a much more intimate way than Vernon in the 'Potter' films is amazing. His intellect is huge. But ... he is not snobbish with the knowledge he has. He shares it and he wants to talk about it. I find him a real joy to be around. For me, it seemed I would have to be really moronic not to take the part."
But there's another reason why he has now tried theater.
"The stage is much more a test of nerve (than film) and seeing what you are made of," Radcliffe explains. "It would be very easy to do simple stuff. It doesn't really interest me that much. Even if I screw up, it's good to know what my limits are. It's good to get a sense of what I can and cannot do.
"Every actor has limits. It's sort of testing out where they are. Luckily, I haven't found them yet. I suppose the thing I've learned is that I think I am more capable than I thought I was," he says with a laugh.
In London, Radcliffe won praise from the critics and audiences for his performance, which includes a brief nude scene, a moment that undoubtedly sold a few tickets to curious "Harry Potter" fans.
"That's the thing about doing it the first time around," he says. "Everyone was wondering if I could ... pull it off. I didn't know whether I could do it (but) I really wanted to ... And I am going to get better this time around as well."
For Radcliffe, training started with his voice. For the past three years, he has worked with Barbara Houseman, a respected vocal coach in England.
"There are a lot of actors who think you can just go on stage and do it - you can't," he says. "You need to project. You can give the most amazing performance on stage but if the audience can't hear you, then it's useless."
Houseman is in New York for the show's preview performances as Radcliffe prepares for opening night at the Broadhurst Theatre on Sept. 25.
"I am a lot more confident about (my voice) being heard now. In London, that was more of a worry. Now there's room for me to do ... to play around with the words and put more color into them, sort of a musicality, to try and give every word its individual identity, I suppose.
"Maybe I am more relaxed this time. I think it's just the fact that I have grown up in the year and a half since we (last) did it," he says. "The other night I got a line wrong, which, for me, was like a dagger because I don't like doing it."
"Equus" is an emotional, disturbing play, a mystery of sorts that steadily builds to a surprising climax. How does Radcliffe unwind from all that intensity?
"I go home and watch The History Channel, which is what I have been doing the last few nights," Radcliffe says with a laugh. That's after he has waded through crowds waiting at the Broadhurst stage door for an autograph or a cell-phone photo op. It's a group Radcliffe is very much aware of.
"Credit your audiences with massive (amounts) of respect because some of these guys see 50 shows a year," he says. Radcliffe admonishes his fellow newcomers to Broadway this season to salute these ticket holders. His advice?
"When you are at the curtain call, smile," he says. "I really object to it when I am sitting there in the theater, watching actors who are in a great play - and they come out and don't smile at the curtain call. I think: 'You are lucky enough to be in a really brilliant play, now show some appreciation for the fact that you are there. Enjoy it.' We're doing 'Equus' and we smile. If you can smile at the end of 'Equus,' anyone should be able to."
Despite his new stage persona, Radcliffe will never be very far away from where he first earned his celebrity - those "Potter" films based on Rowling's seven books.
The movie version of number six, "Harry Potter and the Half-Blood Prince," is already in the can and comes out in July 2009. Filming of the last "Potter" book - "Harry Potter and the Deathly Hallows" begins after Radcliffe finishes his "Equus" run in February.
"I am sure I will be knackered but I adore filming on 'Potter,"' he says. "I can't wait to get back there."
"Deathly Hallows" will be released as two movies - one in November 2010 and the last in summer 2011. Production is expected to take about 14 months. After that, maybe more stage work.
"In 10 years time, I've no clue where I'll be," Radcliffe says. "Hopefully, still acting. If I'm still acting and still enjoying it, I will be happy. I feel pretty certain that will be the case."