As children, we learn to recognize colors through examples of objects described as yellow, red, or blue.
However, the realm of color science encompasses more than just these hues.
In addition to hue, the color scientist considers lightness as a defining attribute.
This article explores the three dimensions of color: lightness, hue, and saturation, delving into their physical nature and interplay.
Lightness
Lightness distinguishes black, gray, and white objects from those with hues.
While black possesses no lightness, white represents maximum lightness.
The color physicist employs a block of pure barium sulfate as the reference for 100% white.
Neutral gray objects can be arranged quantitatively in order of their lightness, forming a gradient between black and white.
Hue
Sir Isaac Newton demonstrated that white light can be split into a full range of hues, including red, orange, yellow, green, blue, and violet, using a glass prism.
These natural hues can be arranged in a circular sequence, completing the color wheel.
By dividing the circle into, for example, 100 divisions, hues can be quantified and measured.
Saturation
Saturation refers to the intensity, strength, or purity of a color.
By adding increasing amounts of a pure hue (e.g., blue) to pure white, a range of colors can be created, varying from pure white to increasingly intense shades of blue.
This process can be repeated for different hues, resulting in an almost infinite array of colors.
Similar to lightness and hue, saturation can also be quantified.
Color Space
Arranging colors logically on a two-dimensional shade card is insufficient due to the three independent variables of color: lightness, hue, and saturation.
To overcome this limitation, color scientists utilize a three-dimensional color space.
This concept allows for a comprehensive representation of colors, considering all three dimensions together.
Reflectance and Color Perception
Colors we perceive are not emitted by objects themselves but are a result of how they reflect light.
Objects we describe as white appear so because they reflect most of the light falling on them.
Conversely, objects that absorb all light appear black.
Objects that selectively absorb certain portions of the spectrum appear colored.
For example, an object that absorbs only blue light appears yellow, while one absorbing red light appears green-blue, known as cyan.
Light Sources and Color Temperature
Light sources play a crucial role in color perception.
When objects are illuminated, the color of light affects how we perceive their hues.
The concept of color temperature quantifies light sources by comparing them to the so-called black-body radiator at various temperatures.
The Kelvin scale is used to measure color temperature, with a tungsten filament lamp having a color temperature of approximately 2800 K and north daylight around 6700 K.
Fluorescent Tube Lamps
Fluorescent tube lamps provide an alternative light source.
They contain mercury atoms that emit light when electrically stimulated.
The emitted light comprises the yellow, green, and violet line spectrum of mercury.
The inside of the tube is coated with phosphors, substances that fluoresce in the mercury discharge.
Blending different phosphors creates lamps with varying color temperatures, offering a range of light tones.
Metamerism and Color Matching Explained
Metamerism is when two objects appear to match in one lighting condition but not in another.
This can be problematic when trying to match prints and fabrics with different pigments or dyes.
Certain types of lamps, like fluorescent tubes, can make this issue worse.
For example, prints and fabrics that look identical in daylight might show noticeable differences under artificial lighting.
This happens because various light sources emit different spectra, which affects how we perceive colors.
To combat metamerism, specialized fluorescent lamps designed for color matching are available.
These lamps emit light evenly across the entire visible spectrum, reducing the chances of metamerism in color assessments.
Moreover, laboratories and dedicated color matching booths use these lamps to ensure precise color evaluation.
Conclusion
Understanding the physical nature of color involves considering its three dimensions: lightness, hue, and saturation.
Lightness determines the intensity of white, gray, and black objects.
Hue encompasses the full range of colors visible in the spectrum.
Saturation describes the purity and strength of a color.
Together, these dimensions form the basis for a comprehensive understanding of color.
Color perception is influenced not only by the objects themselves but also by the light sources illuminating them.
Different light sources emit varying spectra, leading to variations in color perception.
Color temperature serves as a measure to quantify and compare the color characteristics of light sources.
Fluorescent tube lamps offer an alternative to traditional light sources, providing efficient and adjustable lighting options.
However, they can introduce metamerism, causing color discrepancies in different lighting conditions.
Specialized lamps and color matching environments help minimize metamerism and ensure accurate color assessment.
By comprehending the physical aspects of color and considering the interplay between light, hue, and saturation, we can better understand and manipulate color in various applications, including design, printing, and visual perception.
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