One Solar Luminosity: The Sun's brightness-- or one solar luminosity -- is comparable to that of four trillion trillion one-hundred-watt light bulbs. Put differently, if we could harness the energy the Sun radiates in one second, we'd have enough energy to satisfy the current US energy usage for about 4 million years.

Solar Luminosity in Metric Units: Astronomers have their own way of speaking of the Sun's luminosity. They use the metric system. In metric units, one solar luminosity equals 400 trillion trillion joules of energy being radiated into space every second.

Solar Energy on the Earth: The Earth intercepts about one-half billionth of the energy radiated by the Sun. This solar energy gives us light and warmth.