EXCLUSIVE

The back-to-back Democratic debates -- which will feature candidates of Black, Hispanic, Samoan, Indian and Asian descent -- will be a major test for those trying to tackle the issue of diversity ... in the lighting department.

Production sources for the upcoming primary debates -- in which 10 different candidates will share the stage on both nights -- tell TMZ ... the fact they will feature more non-white candidates than previous debates will be challenging.

That company, Lighting Design Group, has experience dealing with crowded stages in the political world -- it did the lighting design for the 2016 Republican primary debates ... which had 17 in the field, but only 2 of those candidates -- Ben Carson and Bobby Jindal -- were persons of color ... and Carly Fiorina was the only woman.

The Dem debates have 5 non-white candidates and 5 women, which we're told can make the lighting way trickier.

Our sources say the lighting pros have to focus on getting it just right for the men and women of different skin tones when the TV shows a solo shot, but also must balance the lighting overall for "broad look" shots of multiple candidates. There are individual spotlights, but other lighting on the stage bleeds into the individual shots.

We're told the lighting folks will be ready to adjust on the fly during the debates with the goal being to make sure everyone is satisfied, but satisfying 20 presidential candidates may be an impossible order.

Here's the full lineup of the 20 candidates taking the stage:

Wednesday night -- Elizabeth Warren, Cory Booker, Beto O'Rourke, Julián Castro, Amy Klobuchar, Tulsi Gabbard, Jay Inslee, John Delaney, Tim Ryan and Bill de Blasio.