Change your photo from dark to bright.
Exposure is the amount of light per unit area reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture, and scene luminance. Shifting your exposure is like changing the in-camera settings in post-production. To be more technical, it scales the settings up and down by a constant multiplying factor. Moving this slider either increases or decreases all of the elements that go into obtaining the correct exposure at once.