The intensity or brightness of light depends on how far the subject is from the light source and the size of the source of light. The closer the subject is to the light, the brighter or more intense the light will be.
It can sometimes be extremely hard to take control of the intensity of natural light. If the light doesn’t change, it is up to the photographer to regulate the aperture, shutter speed, or ISO to get the preferred exposure. When the intensity of the light is low, slower shutter speeds, higher ISOs, and a larger aperture are needed. When the intensity of the light is high, you can make use of quicker shutter speeds, smaller apertures, and low ISOs to achieve the best exposure.
Calculating the intensity of artificial light is quite easy in most cases, and even the built-in flash can be adjusted by using flash compensation. Studio lighting can have multiple lights that are each modifiable, giving the photographer amazing control over the light.
Have a look at other articles describing the influence of lighting conditions on photography:
The Color of Light, Light Direction, The diffusion of light, Light types