Color is a critical aspect of our lives that influences our emotions, perceptions, and experiences. While we may casually refer to colors like “red” or “green” in conversation, quantitatively measuring color involves complex physics and mathematics. In this article, we’ll explore some of the key ways color is measured and quantified.
The Electromagnetic Spectrum
To understand how we measure color, we first need to understand a bit about light. Visible light that we can see is part of the electromagnetic spectrum – a range of different wavelengths of energy that also includes radio waves, microwaves, infrared radiation, ultraviolet radiation, x-rays, and gamma rays.
Visible light is generally defined as the wavelengths that can be detected by the human eye, from about 380 nanometers (violet) to about 740 nm (red). Inside this range, every color corresponds to a specific wavelength. Red light has a longer wavelength (around 700 nm), while blue or violet light has a shorter wavelength (around 400 nm).
When all the wavelengths of the visible spectrum combine together equally, we see white light. The appearance of color comes from when an object absorbs some wavelengths more than others. For example, a red object absorbs most of the spectrum and reflects back mainly red wavelengths.
The RGB and CMYK Color Models
There are two primary ways we mathematically represent color: RGB (red, green, blue) and CMYK (cyan, magenta, yellow, black).
The RGB color model uses the three primary colors of light – red, green, and blue – to create the other colors in the visible spectrum. By varying the intensity of each one, all the colors we see on a computer monitor or television screen can be reproduced. RGB values are generally specified on a scale from 0 to 255.
The CMYK model, on the other hand, is used for print design and productions. Instead of mixing colored light, it uses inks to absorb select wavelengths. Cyan, magenta, and yellow are the three primary colors, with black added for better contrast. CMYK values range from 0 to 100%.
| Color | RGB Values | CMYK Values |
|---|---|---|
| Red | 255, 0, 0 | 0, 100, 100, 0 |
| Green | 0, 255, 0 | 100, 0, 100, 0 |
| Blue | 0, 0, 255 | 100, 100, 0, 0 |
As seen in the table above, while RGB and CMYK define colors differently, there is a direct conversion between the two models. Computer software can translate colors back and forth based on established formulas.
Hexadecimal Color Codes
Hexadecimal color codes are one of the most prevalent ways to specify colors in digital design. A hex code is a 6-digit string preceded by a # sign, such as #FF0000 for red. The first two digits represent the amount of red, the middle two represent green, and the last two represent blue, on a scale from 00 to FF (which is 255 in decimal).
Some examples of hex codes for common colors include:
- White: #FFFFFF
- Black: #000000
- Red: #FF0000
- Green: #00FF00
- Blue: #0000FF
Hex codes provide a concise and convenient way to assign RGB values to colors in coding for web sites, apps, and other digital media.
The CIE Color Spaces
While RGB and CMYK are great for specifying colors in digital and print media, scientists and researchers use more advanced color spaces that aim to model human vision accurately. The most widely used are established by the International Commission on Illumination (CIE).
Some key CIE color spaces include:
- CIE XYZ: Based directly on the human eye’s retina response to different wavelengths.
- CIE Lab: Designed to be perceptually uniform, where equal distances represent equal perceived color shifts.
- CIE Luv: Similar to Lab but with slightly different luminance calculations.
- CIE RGB: A specific RGB space that matches CIE’s color matching functions.
These color spaces allow colors to be specified and distinguished using precise numeric data. However, they require complex formulas and are less intuitive than hex codes for general design work.
Spectrophotometers and Colorimeters
Spectrophotometers and colorimeters are scientific instruments used to measure colors. They measure the intensity of light at different wavelengths that is reflected or transmitted from an object.
Spectrophotometers provide more detailed and accurate color information, but are also more expensive. Colorimeters are affordable for more casual use. Both types of devices are used extensively in industries like printing, textiles, automotive paints, photography, and cosmetics to achieve precision color matching.
Color Temperature
Color temperature refers to the perceived “warmth” or “coolness” of white light. It is measured in kelvins (K) based on the temperature to which an ideal black body radiator would need to be heated to produce that color. Some key facts about color temperature include:
- Candle flame – About 1850K – Very warm yellows and oranges
- Incandescent bulbs – 2700K-3000K – Warm whites with a yellow/orange tint
- White fluorescent – 3000K-5000K – “Neutral” white light
- Electronic flash – 5500K-6000K – Cool white that appears bluish
- Daylight – Around 5000K – Considered the standard reference white
- Overcast sky – 6500K-7500K – Cool light tending towards blue
Choosing appropriate color temperatures for lighting is important for establishing a desired mood and minimizing eye strain.
Measuring Brightness and Luminosity
In addition to color, the brightness of light is an important quantity to measure. Some key terms and units include:
- Luminance: The amount of light passing through or reflected from a surface, weighted by the eye’s wavelength sensitivity. Unit: candela per square meter (cd/m2)
- Luminosity: The total amount of visible light power emitted by a source. Unit: lumen (lm)
- Illuminance: The total amount of visible light falling on a surface. Unit: lux (lx)
Devices like photometers, spectrometers, and lux meters are used to accurately measure brightness and luminosity. Matching light levels and illumination is crucial for proper film, photography, medical imaging, and many other fields.
Conclusion
From the physics of light to the biology of human vision, color is an intricate phenomenon that contains many nuances. Accurately measuring and quantifying color requires complex math and science across disciplines like optics, radiation physics, electronics, neuroscience, and psychology. While we colloquially use color names like red or green, specifying colors precisely involves in-depth understanding of models like RGB, CMYK, hex codes, and CIE spaces. Quantitative measurement helps us reproduce, match, and distinguish colors reliably for a wide variety of scientific and creative purposes.