https://www.nfsa.gov.au/sites/default/files/2025-02/Colour%20TV%20Mega%20Menu%203%20TVs_1000x745%20px.jpg
Photocell
An electronic device that converts light into an electrical signal. When modulated by visible light it produces electrical impulses that can be amplified to drive audio speakers.1 Some cells produce electricity when exposed to light; others react to light by offering an electrical resistance.
https://www.nfsa.gov.au/sites/default/files/uploads/2010/09/28/Schematic_of_optical_sound_reproduction.gif
References
1 Kodak: A Concise Glossary for the Non-Technician
The National Film and Sound Archive of Australia acknowledges Australia’s Aboriginal and Torres Strait Islander peoples as the Traditional Custodians of the land on which we work and live and gives respect to their Elders both past and present.