Both Nikon L840 and Fujifilm S9900w have 16.0 MP resolution sensors but Nikon L840's sensor is 1/2.3' (6.17 x 4.55 mm ) and Fujifilm S9900w's sensor is (1/2. ).
Since Nikon L840's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Fujifilm S9900w.
Below you can see the L840 and S9900w sensor size comparison.
As seen above, Nikon L840 has a infx Larger sensor area than Fujifilm S9900w. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.