I was twelve years old the first time a blind person asked me what color was like. Naturally, I was dumbfounded: how do you describe an experience you've lived with and taken for granted since birth? And such a rich experience at that, filled with emotive qualities -the cozy gold of a late summer sunset, the sensuous crimson of plush velvet curtains at the theatre, the cold silver sheen of a dentist's tool tray, the breathtaking green of a spring meadow... how to tell it?
Having spent weeks researching the topic of our last exhibition, Wonderful Waves: The Science of Sound and Light, I still feel less than fully equipped to answer the question to my own satisfaction, much less that of Toby, my blind friend. But if she were to ask me today, I might rely on the concept of light as a wave form, and compare it to sound, another perceptual experience that depends on waves. Toby was, after all, a musician, and could probably relate to the shifts in pitch and loudness of sound that are analogous to changes in hue and intensity of light.
Sound waves are the result of vibrations of molecules in the air. Slowly vibrating air molecules make long waves, with low frequencies of peaks in the waves. That's a low-pitched sound. High-pitched sounds result from vibrations of very high frequency (measured in hertz, Hz).
When we see colors, we are seeing light of different wavelengths, produced by the vibrations of electromagnetic fields. In fact, we can think of the colors of the spectrum as rather like the notes on an octave, although the "octaves" of a rainbow don't repeat themselves. With frequencies ranging from 3.9 X 1014 Hz (violet) to 7.7 X 1014 Hz (red), the visible spectrum actually occupies less than one complete "octave" of the complete electromagnetic spectrum, which ranges from wavelengths below 10 Hz (long radio waves) to over 1022 Hz (gamma and x-rays)!
Sound can also be measured with respect to how loud it is. Loudness, measured in decibels (dB), is a product of the amplitude of the sound wave - how high the wave is. In the same way, the "loudness" of a light source - how bright it is - is determined by the amplitude of the associated light wave.
Purity - of either sound or color - reflects how many different wavelengths are occurring at the same time. We think of the degree of purity of a note as its tone, and that tone will vary based on how it's produced. A flute makes a purer, more mellow tone than a violin, which has a brighter, scratchier sound. Similarly, light from different sources, or reflecting off various surfaces, has differing qualities of "warmth" or "coolness." In terms of purity, a tuning fork is like a laser beam - both create very pure waves.
Tone may be the biggest factor in the emotional qualities of the experience of sound, but loudness and pitch contribute as well. Think of all the dynamics involved in the playing of a complicated piece of music, and how each aspect affects your response to the music.
So perhaps I could explain color to Toby as like music: "Think of the note A, and all the ways it can sound. Call those sounds reds, and Bs would be shades of orange, Cs yellows. Now imagine a symphony, and you might get an idea of what it's like to see colors in my world." I'm not sure it would really get the idea across, but it's the closest I can think of. Close your eyes and try it!