it does not reflect the darkness of the printet photos, och if I view the photos on photoshop. How to correst the darkness of it?
Lightroom and Photoshop should display images exactly the same.
If they don't, it's usually due to a broken monitor profile.
You should calibrate your monitor with a hardware calibrator.
As a temporary fix you can set the monitor profile to sRGB. See How do I change my monitor profile to check whether it’s corrupted?