Why are my images too dark or light?

Q. Why are my images too dark or light?

A. If your camera is not set to Manual Mode and the images are too dark or too light (under or over exposed) one of the more common reasons for this would be that the exposure compensation is set incorrectly. 

Exposure compensation is a feature found on many cameras that allow exposure to be biased towards under or overexposure. It’s useful in situations that may confuse a camera’s metering system, such as when a scene contains many dark or bright areas.

The Wex Blog post on this link explains in more detail  What is Exposure Compensation?