The two factors that determine exposure and subsequently affect photo brightness are shutter speed and aperture (another important factor that determines exposure is ISO sensitivity, but in the following explanation, we will assume that ISO sensitivity remains constant).
Shutter speed refers to the length of time the shutter is open. The higher the speed, the shorter the time for the shutter to open, and the shorter the time for the image sensor to sense light. The shorter the sensing time of the image sensor, the darker the photo taken. On the contrary, the lower the shutter speed, the longer the image sensor senses light, and the brighter the photos taken.
The aperture (represented as the f-value) controls the brightness of the image that passes through the lens and is imaged on the image sensor. The higher the f value, the darker the image captured by the image sensor and the darker the photo taken. On the contrary, the lower the f value, the brighter the image captured by the image sensor and the brighter the photo taken.
If the f-value is increased, you can still achieve optimal exposure by selecting a lower shutter speed. In other words, if the f-value is lowered, you can still take photos with the same brightness effect by selecting a higher shutter speed.
