Painting on Location
by Donald A. Jusko

colour cat

Diffracting Sunlight

Bending Lightwaves, diffraction, refraction

FREQUENCIES are the number of waves that pass a point in space during any time interval, usually one second. It is measured in units of cycles (waves) per second, or Hertz (Hz). The frequency of visible light is referred to as color, and ranges from 430 trillion Hz, seen as red, to 750 trillion Hz, seen as magenta. The full range of frequencies extends beyond the visible spectrum, from less than one billion Hz, as in radio waves, to greater than 3 billion billion Hz, as in gamma rays.
Violet is where the magenta waves are, the last wave we see before black.
Light waves are waves of energy. The amount of energy in a light wave is proportionally related to its frequency: High frequency light has high energy; low frequency light has low energy. Thus gamma rays have the most energy, and radio waves have the least. Of visible light, violet and magenta have the most energy and red the least.
Light not only vibrates at different frequencies, it also travels at different speeds. Light waves move through a vacuum at their maximum speed, 300,000 kilometers per second or 186,000 miles per second, which makes light the fastest phenomenon in the universe. Light waves slow down when they travel inside substances, such as air, water, glass or a diamond. The way different substances affect the speed at which light travels is key to understanding the bending of light, called refraction.

DIFFRACTION is a light ray angling around a solid object, the ray is white, the shortest wave to angle out of white is sometimes green, the "green flash" seen on the ocean horizon at the moment of sunset. Red. orange and angle a little but magenta, the shortest wave, bends the most. Warm Magenta is also outside the red on the rainbow, and is the last color seen before the dark of night. This is color diffracting, in real time, focusing on a spot inside the shadow's void behind the earth, the center of diffraction.

REFRACTION occurs when the energy of an incoming light wave matches the natural vibration frequency of the electrons in a material. The light wave penetrates deeply into the material, and causes small vibrations in the electrons. The electrons pass these vibrations on to the atoms in the material, and they send out light waves of the same frequency as the incoming wave. But this all takes time. The part of the wave inside the material slows down, while the part of the wave outside the object maintains its original frequency. This has the effect of bending the portion of the wave inside the object toward what is called the normal line, an imaginary straight line that runs perpendicular to the surface of the object.

The amount of bending, or angle of refraction, of the light wave depends on how much the material slows down the light. Diamonds would not be so glittery if they did not slow down incoming light much more than, say, water does. Diamonds have a higher index of refraction than water, which is to say that they slow down light to a greater degree. One interesting note about refraction is that light of different frequencies, or energies, will bend at slightly different angles. Let's compare violet/magenta light and red light when they enter a glass prism. Because violet light has more energy, it takes longer to interact with the glass. As such, it is slowed down to a greater extent than a wave of red light, and will be bent to a greater degree. This accounts for the order of the colors that we see in a rainbow. It is also what gives a diamond the rainbow fringes that make it so pleasing to the eye.

This matches the CMYK color plates on my Real Color Wheel, Magenta extends farther into the cyan on one side of the color wheel making cyan change to Ult. blue as it get darker and farther into the yellow on the other side turning dark yellow brown. Look how far the magenta light waves bend around the moon compared to the yellow waves.

moon shadows

For the full story on a rainbow go here. Rainbows



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