They need to be louvered so that air can circulate and travel through while the machines are running and if the doors are closed. Even after the machines are not running, there can be dampness or humidity in the air. IMO, it is always a good idea to allow laundry equipment every opportunity to breathe and have good air circulation.

Glass doors on a laundry area sound dangerous - make sure they won't shatter if you bump into them. Don't want to die doing the laundry :-) Previous posters here recommend leaving the doors open while running the machines. They get hot, damp and the dryer uses a lot of air. And, if the washer is a FL be sure you can leave the door open and it gets lots of ventilation or you may get biogunk growing in it.

Looking for a little more specific answer: does it matter if the louvers are on the upper half or lower half of the doors?

As for the glass: if used, the glass will be inserts, like glass inserts in an upper kitchen cabinet.

Thanks.

If you do laundry (washing & drying) with the doors open then I don't see a need for them to be louvered at all.
If you do run the dryer with the doors closed, then yes, they must be louvered. Dryers pull a lot of air and must "breath" freely.

Check with your user manual for "closet installation" for the washer & dryer.
I just checked with an Electrolux manual and it states:

"Closet door ventilation required: A minimum
of 120 square inches (774.2 cm�) of opening,
equally divided at the top and bottom of the
door, is required. Openings should be located
3 inches (7.6 cm) from bottom and top of door.
Openings are required to be unobstructed
when a door is installed. A louvered door with
equivalent air openings for the full length of the
door is acceptable."