I recently had a conversation with someone who just started photography. He saw I was using a flash on my camera (bounced off the ceiling) and was curious as to why I did this, rather than “just turn on the lights.” When told the answer, he dismissed it as a pointless exercise. I needed evidence!
That image is taken using in a room lit with 1000w of halogen light. It was VERY bright and HOT in the room. As you see, I set the camera at settings that allowed a reasonable exposure of the scene.
I then set up a flash as the same location (1m from the targets by the way!) I adjusted the flash to a power level that got me a close match to the photo taken using the halogen lights. The camera was not adjusted in any way. The end result was a reasonable match when the flash was as its 1/128th power level, which is as low as it can go.
As a comparison I adjusted the flash up to full power. This time I did need to adjust the camera to return the scene to being “properly exposed.” In actual fact, I could not expose the scene correctly as the flash was FAR too powerful. Even with the camera and lens closed down to allow in the minimum of light possible then scene was over exposed.
Now, to put this into context.
The halogen light was at 1000w of power, which is probably 10 times what a typical front room has. The flash was at 1/128th of its power capability to match this, showing that the flash is MUCH more powerful and capable of lighting a scene than any constant light. In technical terms, the flash is around 6-7 stops more powerful than a 1000w halogen, or 10 stops more powerful than your typical room light. A stop is a “doubling of light” in basic photographic terms, which mean a typical flash on full power delivers over 1000 times the power of light you have in your living room.
All cameras need good light to get a good photo. Poor, or low light, will most often result in a poor photograph. There are ways to compensate for low light, but there are always losses as well as gains. Expect more noise in your photos or blurred scene. However you look at it, flashes are far superior to light bulbs.
(The photos for the examples are simple comparison shots, and are simply to demonstrate the power differences between the two sources.)