photography is to focus the light with the help of refraction so that it can burn the light-catching medium. The medium that has been burned with the right size of luminance will produce an image identical to the light entering the refracting medium.
To produce the right light intensity to produce an image, a measuring instrument in the form of a lightmeter is used. After getting the right lighting size, a photographer can adjust the light intensity by changing the combination of ISO / ASA (ISO Speed), diaphragm (Aperture), and shutter speed (speed). The combination of ISO, diaphragm & speed is called exposure.