One would expect a wedding under a tent would have plenty of light. But why do the subjects keep coming out so dark? Could a flash be an answer?
The issue is not the amount of light available, but the direction and quality of that light. With tent lighting, it’s difficult to make an exposure where the tent isn't in the background. It’s where everything has more light spilling on the background than the faces or the subjects.
It’s very simple to turn on the flash and shoot photos in a tent during daylight. Using a strobe to supplement the light source would provide a well-exposed subject and balanced background. One must match the f/stop and ISO to the outside exposure and adjust the shutter speed for the inside exposure. The easiest way to do this is using a TTL flash.
As it gets closer to dusk, why does the background get too dark? The problem is the flash illuminates subjects closer to the camera, but not the background, which appears darker.
During failing evening light, keeping the flash on automatic may produce properly exposed subjects with dark or black backgrounds. On some cameras, if the flash is on automatic, the camera will drop to its lowest ISO setting. One would most likely be shooting at ISO 100 or 200 in auto flash mode. It’s a default in the camera system to better the quality of the image. Lower ISO’s have a greater dynamic range, photos have less contrast, and the colors are more accurate.
Find your camera manual and read two sections, 1) how to turn your flash on and 2) how to change the ISO. Understanding how to override the camera’s “auto everything” will allow better control of strobe lighting. It will also produce photos that can’t be done with an $8 disposable camera.