David Luiz is sitting on a balcony at Chelsea's training ground, talking pollution. Not from his car, or his flights home — although he does worry about that — but pollution as a metaphor for the negativity that surrounds modern life.

Luiz, obviously, isn't the average footballer. For a start, he uses metaphors.

He also isn't average because of the way he looks, the way he plays, and the glow he exudes as he does. Luiz enjoys himself. Luiz enjoys football. He is not afraid to show it, either.

Chelsea defender David Luiz has been a revelation in his second spell with the top-flight club

Luiz returned to Stamford Bridge last summer after a two-year period with Paris Saint-Germain

DAVID LUIZ'S CAREER 2006–2007: Vitoria 2007: Benfica (loan) 2007–2011: Benfica 2011–2014: Chelsea 2014–2016: Paris Saint-Germain 2016– Chelsea Advertisement

In a world of scowls and poses, there is true delight in Luiz's game, giant, toothy smiles that are its by- product. Luiz is one of those people who, if someone pokes a camera at him, can't resist sticking his tongue out, or pulling a face.

And for this reason, and perhaps some severe assessments of his first time in England, he is not taken as seriously as he should be, as a player.

At 30, with more than 500 appearances in club and international football, and on the brink of adding the Premier League title to the five he has won across Brazil, Portugal and France — plus the Champions League with Chelsea — that might be about to change.

N'Golo Kante has cleaned up the individual awards, Eden Hazard is the aesthetes' choice, but it is Luiz at the back who has transformed Chelsea's season. The club took its first step towards a title that will be confirmed with victory at West Bromwich Albion on Friday night, when Antonio Conte switched to his favoured back three after a run of two defeats and a draw. Luiz's presence made that work.

John Terry is his understudy, but Terry could not have sustained this position through the season. Luiz has made it his own. He has refined his game, played with discipline and awareness, shown all of the control it was previously claimed he did not possess. And he has done this with joy. More than any Premier League player, Luiz adds to the gaiety of nations.

He is someone who, if someone pokes a camera at him, can't resist sticking his tongue out

The Brazilian is on the brink of winning the Premier League title for the first time in his career

I make a mistake. It does not mean I am a bad person

'I think many people enjoy playing football, but they don't want to show that,' he says. 'I'm like this because I remember when I was trying to be like this. I'm like this because I remember when this was my dream.

'I used to joke with my sister, pretending to sign my autograph. "Oh this one is nice, this one is nice." Now I stop the car and people hand me pieces of paper, or they want a photograph. There will be a kid at the training ground, he has one leg. He is talking about playing football, with a big smile, telling me about a goal he scored and I think, "Why am I tired? What is my problem?"

'I think everybody is born pure. You never go to the maternity ward and hold a baby that has bad energy. It's impossible. But after comes the pollution of the world, and that makes people change. The situations, the moments in their life, people do bad things not because they are bad but because they don't have the right support at the right moment.

'If you let the pollution take you, then you start to complain for nothing, for anything. You have to push away the pollution, the negative minds, the negative lies. If you gathered 100 people and asked if they had a problem, you would get told about 100 problems. But if you took one person and showed him all the other people's problems, he would think, "I haven't got a problem". This is the world.

'They teach us to be negative, to complain about nothing. I'm not like this every day. But when I am I think, "Hey, wake up". I start to clean myself, get rid of the pollution. Try to do the right thing. Do I make mistakes? Yes. I go to hospitals, I see people in the beds, I think, "They are better than me". I am feeling pain for nothing. Why?

Luiz points to the sky as he makes way out on to the pitch for recent clash with Middlesbrough

John Terry is his understudy, but Terry could not have sustained this position through the year

LUIZ HONOURS VITORIA Campeonato Baiano: 2005, 2007 BENFICA Primeira Liga: 2009–10 Portuguese League Cup: 2008–09, 2009–10, 2010–11 CHELSEA FA Cup: 2011–12 UEFA Champions League: 2011–12 UEFA Europa League: 2012–13 PARIS SAINT-GERMAIN Ligue 1: 2014–15, 2015–16 French Cup: 2014–15, 2015–16 French League Cup: 2014–15, 2015–16 French Super Cup: 2014, 2015, 2016 BRAZIL (INTERNATIONAL) FIFA Confederations Cup: 2013 Superclasico de las Americas: 2014 Advertisement

'But joy is important in life, not just football. Joy is being serious and professional, too. Joy can be reaching your potential by training hard and being disciplined. Joy can be following the rules you need to follow.

'People have the job to judge the footballer. They must have an opinion. That's normal. What is not nice is when they think they know. To say "He played bad" is different from "He is a bad player". You understand? I make a mistake. It does not mean I am a bad person.

'Some people have the pollution and they attack in a negative way. The judges can become crazy, too. In the past people have said I am not focused. It is not nice when you don't have that respect.'

This is what Luiz has been striving for, throughout his career. Respect. The 'PlayStation footballer' criticism that Gary Neville made early in his career wounded him more than is realised. Even now, he doesn't like to be reminded of it, doesn't understand why it is brought up so frequently, when even Neville has said his view has changed.

Yet Neville was not alone. It was said one of the reasons Jose Mourinho allowed Luiz to be sold to Paris Saint-Germain in 2014 was his optimism. As a defender, not a person; Mourinho likes his defenders pessimistic. He wants them worried about what will go wrong, not confident the plan will succeed.

Luiz scored one of the goals of the season when his free-kick caught Liverpool off guard

The centre back slides on his knees in celebration following his stunning goal at Anfield

'Hey, that is not just Mourinho,' Luiz interjects. 'In Brazil they say it, too. Defenders must be pessimists. I cannot be that. I am an optimist in my life. I'm positive. I always think and dream of the best things. But I know where I am. I don't want to take my small boat and go against a wave of 20 metres. Maybe I can go around the sides, and we'll arrive. I'll try to find a way.'

An instance of extreme optimism, though, produced one of the goals of the season. January 31, Chelsea at Liverpool. Adam Lallana fouls Hazard some 25 yards from goal. Luiz is told he can take the free-kick. But he is carrying an injury. He goes to the touchline for water instead. As he runs back on, Mark Clattenburg blows his whistle.

By now Luiz is striding full pelt towards the scene. Willian is supposed to take it, but senses what Luiz has in mind, and says, 'Go on, go on.' And while Simon Mignolet is back on his heels, and Liverpool are still organising their puny three-man wall, Luiz sends the ball into the top corner off the inside of the right post.

Jurgen Klopp called it world class. 'Two seconds before he was standing next to me, drinking water and talking to Antonio Conte,' he marvelled.

The 30-year-old spoke to Sportsmail's chief sports writer Martin Samuel at Cobham

He says: 'In Brazil they say defenders must be pessimists but I am an optimist. I'm positive'

Everyone thought Conte was crazy when I came back

I tell Luiz it is probably my favourite goal of the season. He wonders why.

'Because it's one guy thinking differently from everybody else on the field.'

'Like Hazard does every game,' he says.

'No, because he is thinking instinctively. This was intellectual.'

Finally, he accepts the compliment. 'No, I understand,' he concedes. 'I like this kind of stuff, too. Also, I take the risk. If it goes 20 metres over, everybody will be, "What's he doing? He didn't put his body in the best way. He was greedy. He's crazy."

'I'm not saying I'm cleverer than everybody but when the referee blows the whistle all the players take a big breath to prepare, and in that moment they are not ready. I know this, because I will do it too. The Liverpool goalkeeper is one of the best in the world. If you give him time he will do much better. So I waited for that breath.'

The Brazilian enjoyed a successful spell in France with PSG - pictured playing against Chelsea

The defender looks to tackle Luis Suarez during a Champions League quarter-final tie in 2015

He is a bright guy, Luiz, but not through formal education. He speaks English and French, as well as Spanish and Portuguese, and can get by in Italian and, often, language skills are learned at home. Yet Luiz didn't speak any language except his own when he came to England in 2011.

He worked hard at his classes here because he wanted to communicate with people. He still does. Kante, Chelsea's player of the season, is very quiet and speaks French.

Staff say it is Luiz who has brought him out of his shell, brought him into the group, used his French to communicate and create team spirit where previously — well, we all know what happened last season.

People and relationships are important to Luiz. 'Trophies are nice, titles are nice, shining your armour is nice,' he says, 'but moments with people are special.

'Maybe we will meet again in a couple of months; maybe never more. So this is our moment, because we do not know what happens from here. I try to keep the people who touch my heart in my life — friends, parents. I have two friends who live with me, my girlfriend lives near, my parents come over a lot, on my birthday it was my sister and her kids.

Luiz and Fernando Torres celebrate Chelsea's historic Champions League triumph in 2012

Luiz climbs onto the crossbar to pose for this famous picture following win over Bayern Munich

LUIZ'S 2016-17 STATS Appearances: 31 Minutes played: 2776 Goals: 1 Successful passes: 1228 Passing accuracy: 83.14 per cent Recoveries: 181 Clearances: 159 Headed clearances: 94 Advertisement

'I remember the first time I said a bad word in front of my sister. My dad sat me down at the table. I had a different attitude then, not the right attitude. "What do you want for your life?" he asked. I said I wanted to play football. "No," he said. "First you must become a good human. I want you to become a footballer, too. But first you must be a good human, with honesty, character, dignity." It was a difficult conversation, but it changed my life.

'My examples were my parents. They were not my friends like this new generation. If your mum and dad are your friends, the bad things you do with your friends you will do with your mum and dad.

'They were the people I listened to, who had their feet on the ground, were humble, who had a simple life. My life has changed a lot, but sometimes I stop and I look to my mum and dad and they're still the same people.

'It was my dad's dream to become a top professional. He got to the brink of the first team at Atletico Mineiro but the money was not there, so he had to take another job. He used to say to me, 'This is for you, it was not for me. I will live this with you.'

Luiz opened up on growing up in Brazil and how he has grown as a person while in England

The defender was speaking at his side's training base ahead of their clash with West Brom

'I was training with Sao Paulo which was a long way from where we lived and I didn't get home until 4pm. When my dad thought I could succeed he went to the court and got authorisation that I study at night school. That was my first shock because it was for older people who didn't have the chance to study — but I was 12. So all my school friends were 25, 35 — one was a woman of 65.

'It was great to see how she still wanted to learn. I used to help her. But I started to learn and know things, that were not for my age. There were drugs around, guns around — I think football saved me many times. People might say, "No, he's not part of that life. He's our footballer." And they would leave me alone.'

Rejected by Sao Paulo, Luiz tried out for America Mineiro —'the only time in my life I knew hunger, I ate beans in a liquefier twice a day for 10 days, they wanted me to sign but I didn't go back' — and was then invited for a trial at Vitoria in Salvador, 1,260 miles away. He was 14.

'I asked my mum to pay for the flight,' he recalls. 'It was too far by bus. We had to pay in instalments because only rich people flew. I was playing No 10, and on the bench. We used three defenders, nice, like Chelsea.

'We were going to this competition in Santiago, Rio Grande do Sul — it was 75 hours by bus from Salvador. Two of our defenders got injured on the journey but our coach did not want to change the system because our wing-backs were the best players in the team.

During his first Chelsea spell, Luiz was part of the team which lifted the 2013 Europa League

The Chelsea team celebrate from an open top bus following CL and FA Cup triumphs in 2012

Mourinho says defenders must be pessimists but I can't be

'We had one spare defender. "Who else can I play?" he asked. I told him, "Me." He said, "But you've never been a defender." I told him, "Now I am." He trained two days with me in the middle, I played and was voted best defender in the competition.

'I returned to Salvador a defender. That was a year before I became professional. You cannot make your opportunity happen, you have to see it when it comes. I took a risk and it changed my life, it changed my family's life. Sometimes people lose opportunity because they don't want to try, they don't see the possibility.'

It could be another of those metaphors, perhaps for Chelsea's season, or for Luiz's decision to return to London. How often does second time around work in football?

Yet Luiz has been a revelation. Conte is getting the credit, and no doubt his attention to detail is a big factor, but Luiz has grown, too. He has learned to temper his game, that he can have greater impact playing with more patience, even restraint. And, being Luiz, he refuses to separate personal and professional growth.

Luiz scored this spectacular and decisive free-kick in Brazil's 2014 World Cup quarter-final win

The centre back and Brazil team-mates were embarrassed when Germany won semi-final 7-1

'Maybe the team is more tactically disciplined,' he adds. 'What I know is I am a better player, a better person, a better brother, a better boyfriend, for sure. I know more things, I have more experience. If my friend came to me crying I know what to say to him, or whether to say nothing at all and just hug him.

'It's like football, I know things a bit more now. I think in a different way. I love our system. It has helped so many players. But, don't forget, we had also lost games.

'If the manager had started the season playing Victor Moses at right wing-back, everyone would have said, "He's crazy — go back to Italy." But with the right circumstances, he's had an amazing season.

'Everyone thought he was crazy when I came back, too. But I know my role. Cover everybody, cover the space. It is not the best position for me with the ball. Gary Cahill and Cesar Azpilicueta touch the ball more than me, because all the strikers stay with me.

He got his first taste of football in Europe when he joined Benfica, initially on loan, in 2007

After three seasons in Portugal with Benfica, the Brazilian star first signed for Chelsea in 2011

The strikers are making it boring for me in England!

'They want to make it boring for me in England, because everybody knows I love to play. But I know more about football now. I know why people play good, why people play bad and I have to play for my team.

'Before maybe I got frustrated if my team was not controlling the offensive side, and I would lose my position. I would try to do it myself, which was part of the plan in Benfica. My job was to drive the ball to the halfway line. Chelsea didn't have that plan, but sometimes I would do it anyway.

'I like defenders who are always looking to transform a defensive ball into an offensive ball, I like this style. Good football. I don't like the ones who never touch the ball, say, with their left foot.

'But now, I know you cannot always play this way. If they don't want me to play football, I will find space to touch the ball and try to make the difference another way. Now I manage my game.'

But with joy. Even this patient, watchful, grown-up Luiz. Always with joy.

The Diadema-born footballer poses for a picture taken by Sportsmail's Graham Chadwick