Early on I learned that setting off a flash at night , would only get you out to about 20 feet. thereafter, total blackness.
That is not an Absolute Truth.
While at college, I watched a friend taking photos at night from the 7th Floor balcony of a mob of guys literally across the street during a the Panty Raid. I estimated it was 100 yards or more. I made an inquiry as to Would that photograph be under-exposed? He set me straight real quick.
This guy was a camera bug. He was using high-speed black & white film which helps tremendously at night. The Flash this guy used was something like you see used by a wedding photographer. At weddings, you will see them point the thing up at the ceiling and that is for 2 reasons: it creates a nice soft, artifical light and the flash is soo powerful.
If you have a Flash with enough candle power (or whatever the term), then it can work at night.
Also, if you remember your physics, the strength of the flash decreases by the square of the distance. So the illumination power at 20 feet will be 1/4 of that at 10 feet ---not 1/2. Then at 30 feet it will be decreased to 1/9. Or is it the cube of the distance? Something like that.
Steve
And if you are too young to know what a Panty Raid is then I won't corrupt your mind. Our hicksville college was a little behind the times and that was what they did during exam week.