That will be a very tricky question to answer. LED's on or off, brightness, brand, model... etc.
If the camera gives you an average runtime on a battery, you can divide the battery size (7-8-9Ah) by the runtime.
In the case of my Marcum pancam, it comes with a 1.3Ah battery and will run 6-8 hours. This yields a power draw of .1625 to .25A
Inc