Light from the sun brings energy to the earth... energy that can be absorbed by plants for photosynthesis, by the oceans to evaporate water and cause rain, by photocells and solar panels to create electricity, and so on.

When light enters the human eye and falls on the retina, it sets off photochemical and neurological processes that result in seeing. Radio waves, television transmissions, microwaves, ultra violet light, X-rays are all forms of electromagnetic waves just like light, but with a different wavelength. The human eye cannot perceive these wavelengths, but instruments can pick them up.

Thomas Edison invented the first practical electric lamp in 1879. He also invented the phonograph, moving pictures, the mimeograph machine, carbon microphones and so on. Edison's original lamp used a carbon filament in a vacuum. Today we use tungsten wire in a bulb filled with argon gas.

Edison's original lamp converted less than 1% of the electricity into light. Today's household bulbs convert 6% to 7% into light, the rest being wasted as heat. Compact fluorescent lamps today can be 50 times more efficient than Edison's original lamp and will last for years.