This page describes various forms of notation used to describe colors.

This might seem overly geeky, but it gives you a foundation that can be used to understand color mixing. It helps if you already know how color vision works.

• Wavelength
• Spectrogram
• Color Temperature
• Tristimulus-Based Systems
  • RGB
  • CMYK
  • Maxwell Triangles
  • CIE Chromaticity Diagram
• Opponent Color System
• Hue-Saturation-Value (HSV)
• Hue-Lightness-Saturation (HLS)

• For More On This Subject
• Related Wolfstone Pages

This is a highly accurate method of specifying a color of light, but only works for monochromatic sources. This makes it useless for recording fake colors, like purples and pinks.

Every element has a different spectral signature of light that it emits. Here are some simple emission spectra:

It is not necessary that the spectrum be depicted in color. All that really matters is the position, width, and intensity of each line.

I just faked this by replacing the colored lines with white. But it clearly illustrates that each spectrum is different, even without color in the picture of the spectrum.

You could also draw a simple graph of intensity versus wavelength, or in the case of a filter how much light it transmits versus wavelength.
This is the Spectral Energy Distribution curve for Rosco's Roscolux #342 Rose Pink gel filter.

When the material is heated, it starts to glow with emitted "black body radiation". This is the principle of "incandescence".

As the temperature gets higher and higher, the emitted radiation becomes more and more energetic, with a shorter and shorter wavelength. From invisible infrared, it goes to red, orange, yellow, and so on through the visible spectrum. The common expression "red hot" comes from a simple, every-day observation of black body radiation. Early texts on metalworking described the temperature with similar observations, like "heat the iron until it glows with the color of yellow straw."

One important benefit of light production via black body radiation is that the light is composed of a continuous spectrum of colors. So when you heat something from red hot to orange, it continues to give out some red light, but also gives out orange. This continuous spectrum gives good color rendition when the light is used to illuminate objects.

The tungsten filament of an incandescent lamp acts much like the ideal black body, and produces a continuous spectrum of light.

You don't get such a spectrum from the arc of a gas-discharge lamp or even a fluorescent lamp. All of these light sources produce sharp bands or spikes of color, and are considered "broken spectrum sources". For such light sources, color temperatures don't precisely apply. Although the eye will not notice the broken spectrum, color shifts can result when the light is processed by machinery, including photography.

Color temperatures are given on the Kelvin scale, and the tendency is to write them with a "K", but without the degree symbol. I prefer using the notation "°K".

The following table gives some approximate color temperatures. Entries marked with "*" are broken spectrum sources.

color temperature, °K	light source
1500	candle light
2680	40 W incandescent lamp
3000	200 W incandescent lamp
3200	sunrise/sunset
3400	tungsten lamp
3400	daylight, 1 hour from dusk or dawn
4500-5000 *	xenon arc lamp
5500	daylight, sunny day around noon
5500-5600 *	electronic photo flash
6500-7500	overcast sky
9000-12000	daylight, clear blue sky

You will notice that there are several different values for daylight. This is because sunlight must travel through our atmosphere, which tends to scatter blue light. This is why the sky is blue. When the sun is directly overhead, the light travels perpendicular to the earth and passes through a minimum of atmosphere, and keeps more of its blue content. In the early morning and late evening, the sunlight must travel at a tangent to the earth, through a much larger quantity of atmosphere, and loses much more blue light, giving a red look. [There are other factors that affect the color of sunlight, including: geographic longitude and latitude of your position, the amount of smog in the air, and weather conditions like clouds.]

In this system, any color is defined by three numbers, which correspond to the amount of light from three emitters that roughly correspond to the peak sensitivity of each of the three types of cones in the human eye (red, green, and blue).

The range of numbers that each R, G, and B value take on depends on the exact system you are using. There are a variety of ranges:

• integers 0-255; often used in computers, web pages, etc
• integers 0-100; often used where a "percent" is easy to deal with
• decimals 0-1
• or anything really

In theory, you could produce any color by simply mixing the three pigment primaries of Cyan, Magenta, and Yellow. In practice, it gets messy when you want to get really dark shades, so black is also used.

You are likely to find this in print shops and color computer printers. In theory, you might find this in paint mixing at your local hardware store, but in practice they prefer to use a large array of different colors in order to minimize the amount of tint that must be added to the base paint.

• The web site of Earl F. Glynn II has a lot of information on colors, fact-packed and well presented.

• how color vision works
• color systems [this page]
• color mixing
• coloring light

Thank you for visiting. Your comments are welcome.
. . . . . .