Please help. Does sensor size matter in exposure.

I mean, Does a smaller sensor camera need bigger aperture, higher ISO or longer shutter speed to achive the same exposure. I tried to compare 3 Nikon cameras:

• P7000 with its 1/1,7 sensor

• J1 with its 1 inch sensor

• D90 with its APS-C sensor

I set all the camera to the same exposure values (F4, 1/20s, ISO1600)

Results are puzzling. P7000 is a lot darker than D90. I set inadvertently J1 to F3.8 but if sensor size mattered that much, why is J1 shot exposure so close to D90? Is the J1 sensor more sensitive? I checked Dxomark and Nikon aren't cheating that much in ISO values for P7000.

Could you help me understand please. I'm about to throw to garbage all my bright lens compacts. F2 on a compact means nothing if it's equivalent to a lot smaller aperture on a DSLR or even J1.

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Photography has to remain a pleasure, keep PP minimal!
http://www.flickr.com/photos/altruisto/
https://twitter.com/# ! tarekmrad
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owning a Nikon D90, and a Nikon J1
--
Photography has to remain a pleasure, keep PP minimal!
http://www.flickr.com/photos/altruisto/
https://twitter.com/# ! tarekmrad
http://www.facebook.com/tarekmradrtci
owning a Nikon D90, and a Nikon J1