French physicist known for his invention of the oscillograph and for his development of a system of photometric units (photometry) of measurement.

Blondel became a professor of electrotechnology at the School of Bridges and Highways and the School of Mines in Paris. In 1893 he invented the electromagnetic oscillograph, a device that allowed electrical researchers to observe the intensity of alternating currents. In 1894 he proposed the lumen and other new measurement units for use in photometry, based on the metre and the Violle candle. His system was endorsed in 1896 by the International Electrical Congress and is still in use with only minor modifications.

Blondel also contributed to developments in wireless telegraphy, acoustics, and mechanics and proposed theories for induction motors and for the coupling of alternating-current generators.