ᐅ Slatted blinds for windows – Do they provide good blackout?

We are considering fitting all the windows with venetian blinds.
We think they look stylish from the outside.
But are they practical? Can the rooms be darkened effectively with them?

Looking forward to your experiences.

Thank you

What exactly do you mean?

Blinds?

Yes, the blinds. Not regular shutters.

Or do you mean venetian blinds?

Are we talking about the interior or exterior? Fabric, plastic, or metal? Is it about darkening or thermal insulation?