Originally posted by carver9
When? What part of that scene makes you believe he reacted to it?
He's actually surprised. Do you see his eyes? They are larger than normal. He knows he's in trouble as he sees Swampthing is coming out. If his perception was slower than lightspeed then Superman would have still had that confident normal nonchalant look in his eye just like he did on the panel before.
Here's the math. Let's say the average length of the exposed surprised eyeball of a man of Superman's size is 3/4in or 0.75in (it's actually less than this). This is equivalent to 0.01905m. I measured a friend's eye in the surprised mode who has larger than normal eyes.
Light moves at approximately the speed 3 x 10^8 m/s.
Let's assume that Superman first realized that Swampthing was moving the speed of light after he already moved 8 times this distance of his eyeball length (I took a ruler and measured his eyeball against the length of the blue outside the yellow field).
So Superman perceived something moving at the speed of light after 0.1524 m of distance. Now perception time is distance/speed.
So Clark's perception/reaction time is 0.1524/3x10^8 = 5.08 x 10^-10 s.
This is about half of a nanosecond or 508 picoseconds.
Now we know that Superman perceived Swampthing closer than the full 8 times distance since it took time to open his eyes to the larger surprised distance. So his real perception time was much lower. Also the eyeball length of the average surprised male is less than 0.75in. Using a lower number will make the perception time even smaller.