Images: 1940 General Electric brochure cover; portion of 1939 patent drawing from https://www.google.com/patents/US2148315 .
“The sealed beam headlamp, a major advance in automotive lighting was introduced after a three year long development program in August of 1939 [when] General Electric in cooperation with other lamp manufacturers and the American Association of Motor Vehicle Administrators publicly introduced the new headlamp…”
Excerpt from : http://theoldmotor.com/?p=119348 .
This was a major development for motor vehicles. Previously, lamps composed of separate bulb, lens and reflector parts became ineffective due to dirt and deterioration of the silvered reflector. Those problems were eliminated by the adoption of the new units that had these components sealed into a single lamp that also had standard dimensions so they would fit into any of the 1940 vehicles. The new vehicles with these headlights were available for sale in the fall of 1939.
For more info, follow the link to a 1939 auto trade magazine article in the excerpt link above (scroll down about 1/3 of the page).
These brochure images compare the high- and low-beam feature of the lamps.
Image: detail of 1940 Studebaker brochure from http://www.oldcarbrochures.org/index.php/NA/Studebaker/1940-Studebaker/1940-Studebaker-Champion-Brochure/1940-Studebaker-Champion-08 .