Exhuast & intake air

I just finished my room 2 weeks ago with alot of help from the forum & the people here. I have a question for the pro's. Would a 4" dryer vent be enough intake to vent a room 5x5x8? My exhuast fan is 15 inches around, I have no idea as of the size of it because its a old fan from a green house. I have a 16" fan blowing air & 5 27 watt cfl lights. I made a mistake and put my plants in before I had an intake air supply & now I have yellow spots. I just wanna make sure I do this right since I worked so hard & read so much.
I have looked through the forum for the answer & they are many but I would just like to be sure. I live on 200 acres of swamp land & im not worried about the smell so any advive would be gr8! Thx in adv. I also posted some pic,s of my room & my fan & my 3 bag seed plants that were posted in the intrduce yourself forum months ago.

Generally speaking I have read on here that if you are using a passive intake it should be 2x the size of the exhaust hole. All of this is very generally speaking. I personally have not built enough cabs to accuratly test this assumption.

The best advice I would give you is to cut a 4" hole and test the temps. If they are too high then increase it from there. Better to start smaller than to go super huge.