I think it says a lot about our species that one of the most fundamental inventions of our history, the incandescent lightbulb, has been used largely for what it does worst: produce light. The majority of the energy powering a lightbulb goes to producing heat, rather than light. Some sources say as much as 90% of that power is lost to heat, leaving the paltry 10% producing light.
Now picture all the millions of lightbulbs out there, being powered by thousands of power plants, all of them working much harder than they should be, simply to produce artificial light.
What Edison should have done was to figure out how to make a never-ending wax candle. I bet there was real money in that.