Agreed, it's a "some kinda lighting system" and very unlike what we use for growing.
From "Material and Methods" - "To study the photosynthetic response of C. sativa under different PPFD and temperature levels, leaves of twenty vegetatively propagated, four month old plants from a single mother plant…" The leaves are placed in the leaf chamber and the leaves can then be analyzed in a highly controlled environment.
To me, it's a strange set up but my thinking is that the method they chose was/is standard in the pointy headed world so I didn't dig any deeper into it.