Lennon watched his side take a shock lead in the Nou Camp through Giorgios Samaras after 17 minutes.
The Scottish giants had defended bravely and Lennon believes that they can take heart from their performance despite being beaten.
He told Sky Sports News: "We were brave and stuck with what I asked them to do. They defended brilliantly and at times we looked dangerous on the counter-attack.
"Everybody had written us off but I knew of the quality of the character in the team, we just needed to see it through. I look forward to doing it again back at Celtic Park in a couple of weeks."
The defeat means that Celtic fall five points behind Barca in Group G but still hang on to second place at the halfway stage thanks to Spartak Moscow's victory over Benfica.