>>3905147>I'm interested because I want to compare the amount of light that reaches each sq mm of the sensor for these 3 categories."Amount" or "intensity"?
The amount will depend on aperture and shutter speed. The intensity only on aperture.
You don't need a the physical aperture or sensor size if you're interested in amount per square mm.
Take a light meter, place in it a dark tube behind the lens, at a distance equal to where the sensor would stand, and take a reading at ISO100 (on the meter).
Note the light value (=EV at ISO100).
Then use an online converter to convert to footcandles or lux or whatever.
Many meters (usually older ones) have a quick reference for conversion printed in the back, picrelated.
That gives you the illuminance.
Then multiply by the shutter speed to get the total amount of light per square mm.
The physical aperture places no role whatsoever, only the f/number.
