Both Leica V-Lux 3 and Nikon D90 have 12.0 MP resolution sensors but Leica V-Lux 3's sensor is 1/2.3-inch (6.17 x 4.55 mm ) and Nikon D90's sensor is APS-C (23.6 x 15.8 mm ).
Since Nikon D90'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 Leica V-Lux 3.
Below you can see the V-Lux 3 and D90 sensor size comparison.
As seen above, Nikon D90 has a 13.3x Larger sensor area than Leica V-Lux 3. 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.