Reactor having an optimized lighting device

A reactor including a vessel for containing:

• a mass to be treated, and
• at least one lighting device configured to promote the treatment of this mass,
• wherein each lighting device comprises:
• a light diffuser including at least one micro-etched plate transparent to light radiation and having opposite rear and front faces and at least two edges between the rear and front faces, wherein the area of each face is greater than the area of each edge, and wherein the rear face (2113) includes a plurality of micro-patterns (2112), a light source configured to generate the light radiation, wherein the light source is disposed on at least one edge of the plate and is oriented so that the generated light radiation propagates in the plate .