What Is Light?

    Published: 06-16-2009
    Views: 11,392
    Science expert Emerald Robinson explains what light is and how humans perceive it.

    Emerald Robinson: Hi! I'm Emerald Robinson. In this What Is video, we're going to take a closer look at light. What we see as light is only a small part of the electromagnetic spectrum, which refers to many types of energy released from stars, including our own sun.

    Light occupies a space between energy and matter. Light acts like waves, a feature of energy, but also has properties similar to photons, one of the smallest particles of matter. Light travels at the fastest speed allowed by the laws of physics; 186,287 miles per second. Even at these speeds, it takes 8.

    32 minutes for light from the sun to reach earth.

    A light-year refers to the distance light travels in one year, nearly 6 trillion miles. The human eye only detects a tiny section of the electromagnetic spectrum. We interpret different wavelengths of light as different colors. Violet has the shortest wavelength in visible light. After violet, the visible spectrum moves through blue, green, yellow, orange, and finally red, with the longest wavelength.

    Objects you see absorb some frequencies of light but not others. We only see an object's reflected light. We see grass as green because the grass absorbs all light frequencies except green, which it reflects back. In situations where the full spectrum of visible light occurs, such as sunlight, we see the combined wavelengths as white light. If no light is present, we see black.

    An object appears black if it absorbs all visible light frequencies. Light refracts when it passes through glass, water, and our own eyes. Refraction causes the light to bend, changing direction according to Fermat's Principle.

    Fermat's Principle states that light, when entering a substance, chooses a path that takes the least time. As different colors of light have different frequencies, each frequency adjusts to a slightly different path. This effect causes the breakdown of full-spectrum sunlight into the colors we se in rainbows and sunsets.