*8.5. Illumination*

Light energy is critical for accelerating the reaction rate of NP fabrication. The illumination factor affects the intracellular and extracellular synthesis of NPs using photosynthetic organisms [178]. In contrast, some organisms do not need a light source to synthesize NPs. This phenomenon can be attributed to the fact that some organisms secrete different biomolecules capable of NP fabrication, only some of which need light activation [178]. Light intensity may be another important factor controlling the stability and production of NPs [179]. Recently, Ag-NPs were completely fabricated after 5 min using *Azadirachta indica* leaf extract under sunlight [180].
