An exemplary measuring apparatus includes a base, a table, a light blocking piece, a sensor, a luminance meter, a drive assembly, and a controller. The table defines a first elongated slot. A light guide plate is arranged on the table with a central portion of a bottom surface thereof exposed to the first elongated slot. The light blocking piece is attached to the central portion of the bottom surface and exposed to the first elongated slot. The sensor is configured for sensing light and generating a sensing signal. The luminance meter is configured for measuring luminance of the back-light source module. The drive assembly is configured for moving the table to align the light blocking piece with the sensor. The controller is configured for switching off the drive assembly when the light is blocked by the light blocking piece from reaching the sensor.