World's First Interior Frosted Bulb

Filling light bulbs with gas, caused a rise in efficiency, stronger luminosity, and surface illumination also rose.

Because of this, the glare of the bulbs became a big problem for general lighting.
At first, glass bulbs were frosted externally.
This method, however, had a couple of shortcomings; the bulb's surface became dirty too easily, and the transmission of light decreased significantly.
In order to solve these problems, Kitsuzo Fuwa, an engineer at Tokyo Electric Company, had the idea of frosting the inside of a glass bulb.
With considerable time and effort researching, he successfully developed internally frosted light bulbs, which were almost as strong as normal glass light bulbs.