Page "William D. Coolidge" Paragraph 2

Coolidge went to work as a researcher at General Electric's new research laboratory in 1905, where he conducted experiments that led to the use of tungsten as filaments in light bulbs.

He developed ' ductile tungsten ', which could be more easily drawn into filaments, by purifying tungsten oxide.

Starting in 1911, General Electric marketed lamps using the new metal and they soon became an important source of income for GE.

He applied for and received a patent ( US # 1, 082, 933 ) for this ' invention ' in 1913.

However, in 1928 a US court ruled that his 1913 patent was not valid as an invention.