  We theoretically formulate and experimentally demonstrate a secure scheme for
semi-device-independent quantum random number generation by utilizing
Leggett-Garg inequality violations, within a loophole-free photonic
architecture. The quantification of the generated randomness is rigorously
estimated by analytical as well as numerical approaches, both of which are in
perfect agreement. We securely generate $9,19,118$ truly unpredictable bits.
This opens up an unexplored avenue towards an empirically convenient class of
reliable random number generators harnessing the quantumness of single systems.
