White light is the name given to what the human eye sees when all the colors that make up the visible light spectrum are combined; the visible light spectrum is made up of red, orange, yellow, green, blue, indigo, and violet light, and these colors combined make white lighting. When shined through a prism, white lights are broken into the separate colors of the visible light spectrum. Many people commonly refer to white light simply as "light" or "visible light," and it is this light that makes it possible to view one's surroundings. Several sources of white lights exist including the sun and stars, certain types of lightbulbs, and some lamps.
Incandescence, which is visible light created from heat, is the greatest known generator of white light. Objects with lower temperatures emit infrared radiation, which cannot be seen, but as an object gets hotter, the wavelengths get shorter and brighter, moving through red to yellow to white; these white lights are visible to the human eye. In addition to the sun and the common light bulb, molten materials, such as metal or glass, also glow incandescently.
Most light sources are thermal, meaning the type of radiation they emit is a characteristic of the source's temperature. Visible light is primarily radiated by the sun and many other stars. In fact, most of the energy radiated by the sun is within the visible spectrum, which is likely why human beings can see this range of light. Other white light sources include incandescent light bulbs, fluorescent lamps, halogen lamps, white LEDs, and flames.
White light waves are part of the electromagnetic (EM) spectrum, which also includes radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays. The only part of the EM spectrum that the human eye can see without the use of technology is the band of white, visible light. This spectrum is enormous, with waves that vary considerably in size; there are waves that are thousands of miles (kilometers) long, waves smaller than atoms, and everything in-between. Visible light exists in a very narrow band of the electromagnetic spectrum, between infrared (IR) and ultraviolet (UV).
It is the filtering of white light that gives objects color. The sky on Earth is blue because the air molecules filter much of the red light wavelengths out of the white light that comes from the sun. Objects absorb and reflect different light waves to produce all of the colors that can be seen.
Although it is a less common definition of the term, some holistic healers refer to white light as a part of the universe that stores all positive energy. By calling on the white light, it is believed that auras can be cleansed and protected from negative energy. Spiritual healers, yogis, and mystics are among those who attempt to connect with this light, often through prayer and meditation.