Confronted with questions about a flurry of red light camera tickets stamped with yellow times below the 3-second minimum, Mayor Rahm Emanuel's administration said the fluctuation of hundredths of a second was normal — imperceptible to anyone behind the wheel of a car.It turns out that fraction of a second makes a big difference to drivers and to the city's coffers. The Emanuel administration on Friday acknowledged that it had changed the rules on what qualifies for a $100 ticket, quietly directing its new red light camera vendor to tag drivers even when the duration of a yellow light slips just below the 3-second standard set by the city. The policy generated 77,000 more tickets and nearly $8 million in revenue for the city over the last six months. Three days after facing Tribune questions about the short yellow lights, the administration just as quietly suspended the practice on Sept. 22. Called out weeks later by Inspector General Joseph Ferguson, administration officials said they would end the practice for good but keep the money. "My guess is that any safety benefit they can show because of those 77,000 tickets is either nonexistent or very minimal, but they sure do have $8 million more in revenue to show for it," said Joseph Schofer, a Northwestern University engineering professor and one of several traffic experts who have reviewed the Tribune's analysis of the camera program.