I did a similar thing, but I made the top shelf deeper than the bottom shelf (330mm and 530mm). Then, I put a light fitting under the top shelf, which does a good job of casting light onto the bench.
It works well because in practice, kit is a mixture of deep and shallow.
To prevent shelves bending under the weight (which they will, even at 25mm), I added vertical sections which joined the two shelves together. But my design has a rear panel as well - if yours is open, then perhaps this won't make much difference.
Now, a rear panel can make access difficult, but my desk is on heavy-duty castors. This rear panel runs from the bench top to the top shelf, so I can easily access the rear of the deep stuff on the top shelf. It works really well.
The top section is divided up into 19" bays, each of which is 6U high. The whole thing is just over 7 foot wide, meaning that I have four of these. Whether this is worth doing depends on the gear that you have, but it does work quite well for me.
I would have made mine taller, but the headroom is limited in my cellar workshop.
Haven't yet got around to writing up the project, but here are a couple of work-in-progress pictures...
Good luck with yours,
Mark