The lights were suggestive of that part of eye examinations when the optician refines the view with another incremental flourish while asking: “And which one is brightest…now?”

It was a pertinent question for our as yet absent star guest. Had his lately returning form and fitness brought him to the same level as when he illuminated the Bird’s Nest during the Beijing Olympics of 2008? Or were the men standing above him in this year’s world rankings, Asafa Powell, who has run 9.81, and Justin Gatlin, who has been running consistently under 9.80 with a personal best registered in May of 9.74, simply too fast to catch after their flying start to the season?

A pertinent question, but sadly not the most pertinent.

“All I’ve been hearing over the past couple of weeks is just ‘doping, doping, doping’,” Bolt eventually told us after briefly lying his 6ft 5in form back along the length of the sofa.

Prompted by the MC for the event, Colin Jackson - “You OWN the sofa” - Bolt’s playful response was one of the very few lighthearted moments of an interview session which was punctuated on his part by smiles that were rueful rather than joyous.

The blizzard of bad publicity which has beleaguered the sport in recent weeks and months regarding doping, and the fundamental doubts that have been raised have left many athletes feeling like hunted things.

Should they bow to pressure to publicise blood data they don’t even understand in an effort to demonstrate their innocence? Or would this be seen as “protesting too much”? It’s down to individuals’ choice, but for a number of athletes, some of whom I would put very large amounts of money on being clean, the situation is deeply distressing.

The outgoing IAAF President Lamine Diack, challenged on his 16-year legacy at the IAAF’s Championships-opening press conference here, rallied to the cause and spoke doggedly about the innovations in anti-doping which have been instituted by the sport, adding defiantly: “We are convinced that 99 per cent of our athletes are clean.”

How that tallies with Diack’s statement last December, under pressure, that the sport “was in crisis” is an interesting question. But ultimately, trying to catch out an 82-year-old man whose first language is not English is far from the point.

It’s almost a question of faith for many clean athletes now – can they, should they believe that their federation is working honestly to cleanse the sport of dopers?

Among Diack’s other utterances at the press conference was a strong message of praise for the Briton who has won the right to take his place, Sebastian Coe, whom Diack said would do “a great job”.

“In 2015 he is big enough and strong enough to face all the allegations about doping that the sport is facing, and to show that they are wrong,” said the outgoing President..

“He loves the sport, and as a past Olympic champion and world record holder he knows more about it than I did. He knows a great deal, and he will do a great job.

“As the next President has said on the topic of doping, it’s “zero tolerance“ as far as doping is concerned. “What else can you say? Zero tolerance. That’s what it will be.”

Bolt’s comment on Coe was far more wary, but as he pointed out - with another wry grin - he tries to stay away from politics.

“As long as he is good for the sport and he is going to do right by the athletes then I am glad he is elected. We’ll have to see.”

For many observers - particularly media-type observers - Bolt’s part in the forthcoming Championships taking place in the arena where he announced his arrival to the wider world with 100 and 200m world records in the 2008 Beijing Games is seen as symbolic. Ironically perhaps, given the tone of much of the questioning which his 2008 feats provoked, he is now being characterised as the knight in armour who is to slay the doping dragons, with the twice-sanctioned Gatlin serving perfectly as a personification of the opposite extreme.

The suggestion that he was “battling for the soul of the sport” drew another rueful smile from Bolt, as he pondered upon how. “How do you answer that question?” he said, before giving it his best shot.

On the subject of Gatlin: “The rules are there for a reason. If the rule says he can get back in the sport, I can’t really do anything about it, that’s not my call, he can still compete against me.”

On the subject of himself:  “InitialIy I’m running for myself. That’s what I do. People say I need to win for my sport, but I can’t do that by myself. I think it’s also the responsibility of all the other athletes – because I think there a lot of athletes out there who are running clean.”

What is true for Bolt is also true for Coe. Both are hugely important now to the sport, perhaps as never before.

But neither can or should be expected to clean up the town single-handed. This isn’t a Clint Eastwood movie.

Bolt can and surely will continue to be one of the sport’s most appealing and compelling elements – win or lose in Beijing, which, as he hinted more than once, may have arrived a little too soon for him following his belated return to fitness. There’s fitness - and there’s match fitness. Although as he also said, running through the rounds will have more value for him than any other athlete out there.

Coe has a wider brief with which to be concerned. But he is already well into the process of re-setting some of the vital controls at the heart of the IAAF. While he did not assume success, he has planned for it.

That said he, like Bolt, will require many others to step up to the plate in all of newly formed IAAF commissions. The pressure of expectation can’t all be on the shoulders of Coe, any more than in can be on those of Bolt. Right now, world athletics is a team event.

Or as Bob Marley put it: “Let’s get together (and feel alright)”.