The very first Incandescent light bulb was invented by Thomas Alva Edison, Sir Joseph Wilson Swan and Sir Hiram Stevens Maxim. The very first Electric light bulb was invented by Sir Joseph Wilson Swan and Sir Humphrey Davy. As you can see Sir Joseph Wilson Swan is mentioned twice. And no it is not a typo. According to The Myths of Innovation, He and Sir Humphrey Davy developed the electric lights well before Thomas Edison. "When Edison sat down to design the light bulb, he was far from the first person to try." This is a quote from The Myths of Innovation: Chapter 5. In other words, there were a lot of people who have tried to invent the light bulb, but the ones with the most success would have been these 4 men.
Huygens Principle was developed by Christian Huygens and explains laws of ‘geometric optics’. This says that points on a wave front are the sources of secondary waves that spread in all directions. Imagine ripples in water, but along a straight, uniform line. Diffraction occurs when the wave goes through a slit because the wave treats the slit as a new source to ripple from. This is why a voice from a different room sounds like it is from the doorway itself.