What invention by Thomas Edison shed light on people that were in the dark?

What electrodes would you select to produce a weld with shallow penetration E6010 or E6011 or E6013 or E7018? What size wire should be use for connecting a 110 kw motor over a distance of 108 meters? Application of Raman amplifier in DWDM systems? What is the purpose of the zeroing resistor in an ohmmeter and does it always accomplish its intended purpose? How do you control 2 lamps with two way switch? One important effect derived form electricity? Can batteries of unequal voltages b connected in parallel? How does an electric oil burner work? How do you find unknown value of a resistor when two resistor values and voltage are known in a series circuit? How does avalanche breakdown occur in forward biased condition? What size generator 1200 amps? What does water pipes represent electric circuits? What do you means of resister in embedded system? What did thomas Edison do after college? What is the difference between electrical and mechanical devices? What is the working principle of BOD shaker incubator? What does NPN and PNP stand for in transistors? What does electric hand drill mean? What circuit breakers fit into an old Gould Panel GQF40MBB? How did thomas Edison help us understand electricity?