All light meters are calibrated to a standard measurement that reads middle gray. Which means, the range from black to white will be rendered as middle gray, and colors will be lightened or darkened depending on their color hue.
Reflective light meters read the intensity of light reflecting off the subject and incident light meters read the light falling on the subject. The reflective meter is aimed at the subject and the incident meter is aimed at the camera.
Cameras with built-in light meters are reflective. The light meter reads the exposure value of the scene and converts it to shutter speed and aperture settings based on the ISO.
Types Of Metering Modes
Matrix, Averaged, or Evaluated
This type of metering measures the light intensity of many different zones within the entire view finder and averages those results to create the aperture and shutter combination for the best exposure. Matrix metering is used for scenes that need to be photographed quickly and the subject has a mid-to-long dynamic range.