<p>FF sensor is not twice bigger than a m4/3 sensor. It has in fact nearly 4 times more area (it is precisely 3.84 times larger). Two 'stops' of more light actually means 4 times more light hitting the sensor! Light stops (EV) are defined to have a logarithmic curve not a linear one.<br /> The exposure is not directly a function of the total amount of light the sensor receives. It is in fact about the intensity of light per unit of area and that is not affected by the sensor size: larger sensor receives more light but that light is distributed over a larger area so for the same scene and level of available light, exposure is not affected by the size of the sensor. People who say to the contrary of the above, have simply come to believe a fallacy.<br /> If for the same ISO, aperture and shutter speed settings (a certain given exposure setting), you have still observed a difference in the brightness level of the pictures taken with your m4/3 and and with your FF camera, it simply means the manufacturers have not followed the same standard when they were setting up the exposure levels of their camera models. They may do it for their own reasons speculating of which is not the point of this discussion.<br /> Your Sony FF camera has better low light performance than your m4/3 camera which means in high ISO settings you will observe noticeable difference in the noise that is present in the picture. That is the advantage of your FF camera.</p>