Both Panasonic LX5 and Fujifilm Z300 have 10.0 MP resolution sensors but Panasonic LX5's sensor is 1/1.63-inch (8.07 x 5.56 mm ) and Fujifilm Z300's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Panasonic LX5'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 Z300.
Below you can see the LX5 and Z300 sensor size comparison.
As seen above, Panasonic LX5 has a 1.6x Larger sensor area than Fujifilm Z300. 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.