White light is all of the colors of light combined within the visible light spectrum. When white light is separated through a prism, we see the visible light spectrum. The various wavelengths of visible light separate into colors. In turn, when these wavelengths are combined proportionately, we see white light.

The visible light waves that we see are part of the electromagnetic spectrum, the range of all possible electromagnetic radiation frequencies. The range of the electromagnetic spectrum is separated into regions, categorized into smaller spectra based on how the waves interact with matter. Radio waves would be at the low end with longer, low amplitude waves, while gamma rays would be at the high end with very short, high amplitude waves.

The electromagnetic spectrum is enormous, with waves the size of thousands of miles long to smaller than an atom. Visible light exists in a very narrow band of the electromagnetic spectrum between infrared and ultraviolet. The colors within the visible spectrum from lowest to highest amplitude are red, orange, yellow, green, blue, indigo, and violet. One color blends into the next. White light can be made up of infinite combinations of wavelengths the across the visible spectrum. The simplest would be red, green, and blue.

Most light sources are thermal, meaning the type of radiation they emit is a characteristic of the source's temperature. White light is radiated by the sun and stars. In fact, most of the energy radiated by the sun is within the visible spectrum, which is most likely why we see this range. Other white light sources include incandescent bulbs, fluorescent lamps, halogen lamps, white LEDs, and flames.

Incandescence is the greatest known generator of white light. The verb incandesce means to glow white. This is also referred to as black-body radiation. The color of a black body object at high temperatures causes it to glow, and the waves emitted include visible light. In addition to the sun and common light bulb, molten materials such as metal or glass also glow incandescently.

We commonly refer to white light simply as light. It is the filtering of white light that gives us color. Our sky is blue because the air molecules filter much of the red from light. Objects that we observe around us absorb and reflect light waves to produce all of the colors that we see.