Color: The spectrum : Colors and wave lengths : Color theory

We have seen that light travels at an enormous speed of 186,000 miles per second. We saw that this speed was maintained only in the air and that it was reduced when travelling through water or glass.

It so happens that when a beam of light enters a glass prism and is bent; some parts of the beam undergo more bending and pass through a thinner portion than other parts of the beam.

This sets up various speeds of light within the prism and the emerging beam of light, produces what is known as the spectrum, or a rainbow of colours. The colours of the spectrum range from red at one end to violet at the other.

At the red end the part of the spectrum which is bent the least, the wavelengths are the longest and the vibration frequency is the least. The violet end of the spectrum is produced by the greatest bending of the light; here the wavelengths are the shortest and the frequency is the highest.

This spectrum is the result of breaking up white light into its component parts. It must be remembered that white light, or light from the sun, is one unit travelling at a uniform speed and completely unified within itself.

As soon as it is bent or broken up it gives rise to these various wavelengths known as colour, and the process of separating white light into its constituent colours is called dispersion.

The Rainbow

Since the colour depends upon the angle of emergence of the rays from a prism or other “breaking up” surfaces, we can readily see, from our knowledge of internal reflection, how a rainbow is produced. Each tiny drop of rain catches the sunlight, refracts it beyond the critical angle, and reflects it internally back to the eye.

In this process, the light is bent in the same way that it is bent in a prism and colour results. As you view that rainbow, the drops making a certain angle with your eye and the sun as they fall from the sky, produce the colour red; the drops making a slightly larger angle produce the colour orange; and so on down the line to violet, which results from the greatest angle.

Colors and wavelengths

The spectrum may well be compared to the musical scale of seven notes, the red being the first note, orange the second note, yellow the third note and so on up on violet. Each color, like each note, has a vibration frequency and a wavelength; but the frequency, instead of being in the hundreds as in the case of sound, is in the hundred billions.

The wavelength of red light is about 63 millionths of a centimetre, while the wavelength of violet light is about 42 millionths of a centimetre. The visible spectrum is so small a part of the total scale of electromagnetic wave motion that it is almost negligible. The whole range of this wave motion varies from very long radio waves of several kilometres in length to cosmic rays whose wavelengths are less than a billionth of a centimetre.

Note that this wave motion starts with invisible waves that cannot be felt, and as the waves get shorter and the frequency becomes higher they turn into heat waves which can be felt, but not seen.

 As the heat waves decrease in size and increase in frequency they approach what is known as the infrared of the spectrum the head end of the spectrum and if they vibrate still faster and the wavelength decreases still further they become visible and produce the colours of the spectrum from red on through violet.

The vibration frequency of these waves is about a quadrillion. Beyond the violet end of the spectrum lies the ultraviolet or invisible light which cannot be seen or felt; these rays do, however, affect certain chemicals and photographic plates. Beyond this come the x-rays, and then the gamma rays with their frequency of about one sextillion (1,000,000,000,000,000,000,000) vibrations per second. You can see from this that the visible spectrum does not represent a large segment in the vast panorama of radiant energy.

Color theory

The spectrum is made up of three fundamental colour sensations red, green and violet. Where green and violet overlap we find blue, and where red and green overlap we find yellow. We conclude that the combination of red and green lights produces yellow and this may easily be proved by projecting the red light on top of the green light on the white screen. We also conclude that green and violet produce blue a fact which may easily be proved by projecting a violet light on a green light.

Red + green = yellow

Red + violet = pink

Violet + green = blue

This is very important in colour theory. You will note that the secondary colours; namely, yellow, pink and blue are called the primary colours in the paint box. Hence if you have yellow, blue and pink pigments you can very easily get violet, green and red colors. This reveals the interesting fact that light and pigment are exactly opposite.

 When a colored light is projected on a white screen it is reflected back to your eye in that color. When a pigment is put on a white screen it acts as a film that rejects certain colours certain colour to your eye. Just as red, green and violet lights when thrown together produce white; so blue, yellow and pink pigments, when mixed together, produce blackness, which is just the opposite of whiteness.

Complementary colours in lights

Since red, green and violet produce white light, and since the combination of any two colours produces another colour, it follows that any two colours that produce white light are complementary. Red light is complementary to blue light; since blue is a combination of green and violet; and red, green and violet make white. Yellow is complementary to violet; since yellow is a combination of green and red; and green, red and violet make white. Pink is complementary to green; since pink is a combination of violet and red; and violet, red and green produce white.