Digital Cameras: Flash Output Explained
Digital Cameras all come with flashes to give you some extra help when you're in situations with low light. Flash output refers to how much light your flash will actually put out. The brighter the light, the more area it will cover.
Understanding Light and Fall Off
When you look at a photo you used the flash for, you will notice that the foreground with the subject is bright and the background is dark. In fact, the contrast ratio between the foreground and background is very high. This is because of the inverse square law of light. It's a physical law that states the intensity of light in inversely affected by distance.
If a subject is three feet in front of the flash, then he is receiving the full intensity of the flash. But, at six feet, he is only getting one forth of the light and at nine feet he's receiving one ninth. The farther the distance, the more dramatic the fall off. The only way to compensate for this is to have a bright light when you know the distance will be far.
Your flash output refers to how much area is covered by the camera's flash.