sentences:  The increasing scarcity of energy resources, and the environmental costs of producing energy, particularly the discovery of global warming due to carbon dioxide emitted by the burning of fossil fuels, which are the largest source of energy for electric power generation, created an increased incentive to develop more energy-efficient electric lights.The first low-powered LEDs were developed in the early 1960s, and only produced light in the low, red frequencies of the spectrum.In 1968, the first commercial LED lamps were introduced