In the last movie about our Seven Designers for Seven Dials installations, designer Paul Cocksedge demonstrates how calling a neon phone number suspended in the air generates a guaranteed smile.

"What I'm inviting Londoners to do is to phone [the number] and as soon as it rings it begins to flash and you are in direct contact with the piece," says Cocksedge.

While the installation was in place during last year's London Design Festival, anyone could dial the number and the voice of actress Joanna Lumley would answer, inviting the caller to text "smile" to the five digit number that appeared from the original.

She explained that texting gives one pound to children's charity Barnardo's. The donation triggers a neon smile that fills the street.

Dezeen commissioned seven young designers to create seven installations to hang above the streets of Covent Garden during last year's London Design Festival, and Cocksedge's installation was located on Mercer Street.

This is the final movie in our series about Seven Designers for Seven Dials in which each designers describes their installation - see them all here.

Photography is by Mark Cocksedge.

The music featured in the movie is a song called Blue Sapphire by Remote Scenes. You can listen to the full track on Dezeen Music Project.

See all our stories about Paul Cocksedge »
See all more about Seven Designers for Seven Dials »
See all our coverage of London Design Festival 2012 »