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20818
Wound by Light
The Patek Philippe light-wound clocks–‘Pendulettes à remontage automatique par la lumière’ in French–are fascinating.
They use a 17 lines (=38.35 mm) pocket watch mechanical movement (based on a ‘Gondolo’ ébauche), whose mainspring is wound by a micromotor powered by a spark of electric current generated by light captured by sensitive photoelectric cells.
Power reserve is stored in a micro-accumulator with an automatic cut-off device which eliminates the possibility of over-winding.
In other words, with calibre 17-250 E traditional watchmaking meets modern technology.
Here are five references I have selected, with photos showing the “engine room”.
A/ REF. 601 Rhodium-Plated Silver - Manufactured in the 1950s

The
blue and
white circular battery is the
accumulator, which acts as a redundancy system for
powering the
motor which winds the pocket watch movement.

The time-setting "
crown" is located
below the clock.

Henri Stern Agency Newsletter, 1956
credit: Christie’s (1) & Ben Wright Vintage Watches
Advertisement for Tiffany & Co.
Original instruction manual for a Patek Philippe Dome Clock circa 1950s