Katy Perry is proud of her "substantial" lyrics.

The 25-year-old singer said although there is a fun side to her songs - such as the tongue-in-cheek 'I Kissed a Girl' - she is glad to have also penned more meaningful tracks, such as 'Firework'.

She said: "I feel really happy I took that time to not write about DJs and fame, the materialistic world, which is great because I love those glitz-and-glamour bells and whistles, but I know people connect to more substantial lyrics."

The 'California Gurls' star added her latest album, 'Teenage Dream', is particularly focused on her "honest" side, and she is delighted to see fans moved at her live shows.

She explained to MTV: "I started writing songs like 'Firework' and 'Teenage Dream' and songs that I think now are anthems for people.

"When I'm playing 'Firework', the whole arena literally moves up and down. It's the song that people are holding onto and inspired by.

"I always want to be completely honest and, for this record in particular, I knew from the outside world, a lot had changed.

"But when you get to a certain point, you have to push it all away and remember what your core is, and that's what I did for this record."

Meanwhile, Katy has joined other musicians such as Kylie Minogue, Chris Martin and Arcade Fire to donate memorabilia to a charity auction to raise money for earthquake victims in Japan.

A cupcake trampoline stage prop from the singer's 'California Dreams' world tour is up for sale in the auction, which will run throughout April.