Facing the lightbox, walk up to the edge of the balcony where there are no railings. When it reaches the lowest point, jump to land on the metal support that is closest to you.

Then jump to land on the opposite support. Turn left and approach the framework. Lara will grab onto it, so climb up and traverse around to the right.

Climb to the top and pull up.

Take a standing jump to the other corner.

Turn right to face the walkway with the ladder and jump when the mobile lightbox reaches the highest point. If it has lowered a bit, you can press Action, grab the railings and pull up.