Before you listen to this BBC podcast, I'd like to tell you why I love podcasting.

I'm Sasha Johansson, I'm an Assistant Commissioner for the BBC,

and I work on making podcasts. My real passion is discovering unbelievable

unheard stories and working with the biggest stars who can really bring those stories to life.

I love the whole process of making podcasts from the spark of an idea to hearing the final edit.

There's nothing like it.

What makes BBC podcast special is that we're working for you,

so whatever we commission has to reflect the things that you care about and love,

wherever you are in the UK. So if you like this BBC podcast, there's so much more to discover.

Have a listen on BBC Sounds.

How many of you have had sleep problems?

Maybe it's waking up in the middle of the night and they're not being able to get back to sleep,

or waking up too early, or nodding off regularly in front of the TV,

or more embarrassingly during work meetings.

One things for sure, our modern world means that we're not sleeping in the way we used to.

As my guest today, Dirk Yandike says,

we are the only species to extend our day using artificial light,

and that has consequences.

Dirk Yandike is now a distinguished professor of sleep and physiology at the University of Surrey,

and director of the Surrey Sleep Centre.

He moved to Guilford after giving up a faculty position at Harvard University

over two decades ago to set up his research programme,

...