White Light & Colour

White light looks like it has no color at all, but it is really a mixture of every color of the rainbow, all traveling together. You can prove this with a glass prism. When light passes from air into glass, it slows down and bends. Each color bends by a slightly different amount. Violet light bends the most, and red light bends the least, with orange, yellow, green, blue, and indigo in between. So when white light goes into a prism, the colors spread out and come out as a beautiful band called a spectrum. This spreading is called dispersion. Rainbows work the same way. After it rains, millions of tiny water drops hang in the air. Each drop acts like a tiny prism. Sunlight enters a drop, bends, bounces off the back of the drop, and bends again on the way out. Because each color bends a different amount, the colors separate, and we see a rainbow shining against the dark sky. So the rainbow is not painted in the sky. It is sunlight being sorted into its hidden colors.

Scientists who study light use some handy words. Here are a few worth knowing. A continuous spectrum is a band of light that contains every color in a smooth, unbroken range of wavelengths, like the rainbow you get from a prism. Dispersion is the spreading apart of the different wavelengths in white light. It happens because each wavelength refracts, or bends, by a different amount when it passes through something like glass or water. That is why a prism can split plain white light into its hidden colors. An absorption spectrum is the opposite kind of pattern. It is a continuous spectrum with dark lines missing, because something in the way absorbed those exact wavelengths of light. A blackbody is an imaginary perfect object that absorbs all the light energy that falls on it. Nothing real is a perfect blackbody, but the idea helps scientists understand how things absorb and give off light.