Check out this picture.
These camera flashes are just awesome (well, they look awesome). They are not a very useful thing for pictures in this case. Here is the problem. Well, first here is what the flash on a camera is supposed to do. Suppose there is a camera and a ball in a dark room. In order to get light to reflect off the ball and be detected by the camera, you need light. The flash is that light. You can think of it like a flashlight that is only on for a moment. It doesn’t need to be on for long since it doesn’t take very much time to get an image.
Notice that I drew red arrows for the light reflecting off the red ball to represent red light. Ok, back to the problem with a flash in a football stadium. The thing I want to focus on is how much light from the flash hits the object of interest. How do you measure the intensity of light? One way is to look at the intensity in Watts/meter2. As an example, suppose I have a 100 Watt light bulb that produces 20 Watts of light (I am just making up stuff here). If this light radiates equally in all directions, then at 1 meter away I can make this diagram:
So, 20 watts over the area of a sphere with a radius of 1 meter would give an intensity of:
The problem is that camera flash does not radiate the same in all directions. However, if it is a spherical distribution the intensity will still decrease as 1/r2. For the above case, let me assume that the flash is designed to have an intensity I3 to work at 3 meters (I just made this up – I don’t know the optimal flash distance). How bright would this flash appear at the distance of the skydiver in the stadium? Assuming that light is spherically distributed:
What if I want to use the flash for something that is 50 meters away? The intensity at the subject of interest would be just 0.0036 times the intensity at 3 meters. This is probably not bright enough to make the image turn out brighter. Don’t forget that this light reflecting off the subject is also mostly spherically distributed. This makes the problem even worse.
So, why are these flashes on then? Well, the camera sees something dark and just assumes that you need the flash. Plus, it looks pretty. Here is a short video clip so you can see how the flashes change.
Check out all the red lights. I am pretty sure that those are light from video cameras (or phones that do video). Isn’t it standard that in video record-mode there is a red light? If you watch the video, you might notice that you can only see the red lights when my camera is on the opposite side of the subject (the skydiver).