A light might not help you. The police might think that it's a laser sight, and be even more likely to shoot you:
The officers claim that the Taser projected a red light, which they assumed was the laser sight of a handgun, and feared for their lives. At 7.18:43pm, Schiff and Sawyer began barraging Nieto with .40-calibre bullets.
Well, people have been shot with far less obvious things on their hands mistaken (or "mistaken") for guns.
Besides, what phone camera has a light on it that's visible?
None that I can think of in day/noon/afternoon time. Some have a focus assist light and/or flash at night time -- but taking out of one's pockets and pointing a small object at a US policeman at nighttime, and especially in an aggressive scenario as the one we're discussing, that I would advise even less.