Color is a fickle thing, as anyone who has ordered an item online only to have it arrive in a completely different shade will tell you. Similarly, two articles of clothing matched in the closet can suddenly appear to clash in daylight.
Color brings beauty to our world, but can be infuriating in its apparent subjectivity. Why is it impossible to remember the color of an object when our eyes are capable of detecting the tiniest differences?
Quantifying color can be equally frustrating until you understand the factors that affect how it is perceived. That chameleon-like sweater? It’s not in your imagination. Read on and we’ll try to put it all in black & white for you.
- Quantitative: Far more accurate than human eye, with detailed spectral information.
- Flexible: Data acquired can be used to calculate multiple color parameters, varying factors like the observer and illuminant, even at a later date.
- Comprehensive & multi-modal: Other metrics can be simultaneously measured, like brightness and output power for efficiency calculations, or other spectroscopic techniques.
- Objective: Does not depend on a particular set of filters or an algorithm applied at time of measurement.
- Remote access: Fiber coupling allows measurement in hostile environments without impact to the spectrometer.
- Research and Education
- Life Sciences
- Materials Identification
- Farm to Table Technologies
Other Common Applications
- Electronics manufacturing: binning of LEDs, quality control of LCDs and plasma screens
- Lighting: monitoring lamps used in horticulture, hydroponics, street lighting, advertising signage and hospitality lighting; characterizing light sources for CCT, CRI
- Medical diagnostics: assessment of tissue for skin cancer
- Food & agriculture: standardizing orange juice color, assessment of raw cotton quality
- Biology: measurement of leaf disease states, organism coloring as a function of environment, impact of plumage on bird behavior, correlations between frog skin color and pollution levels
- Industry: standardizing anodization, quality control in polymer manufacture, curing of ink and paint
- Art and textiles: mapping the “pixels” in a painting, quality control of fabrics, paint matching systems at hardware stores
What Is Color, Really?
Color is the sensation produced when light at visible wavelengths falls on the human eye, specifically from 380 – 780 nm. Do dogs see in color? Yes, but not the kind of colors we see. That’s because they are physiologically different from us.
Cone cells don’t actually detect color directly. They respond only to the energy they absorb. A single cone cell can tell only whether two objects reflect the same amount of light, not whether they are the same color. The magic comes in their variety. The human eye has three different types of cones, each with its own unique spectral response function. It is the combined and contrasting responses of these three types of photoreceptors that create the impression of a single color in the human brain.
The spectral responses of the three cone types correspond roughly to red, green, and blue – what we consider to be the primary colors in an additive color model. Inspired by this trichromatic response of the eye, many color spaces have developed which use three values to describe color: RGB, XYZ, L*a*b*, and uvw, to name just a few.
Though the individual values in these color spaces don’t correlate directly to the response of a particular type of cone cell in the eye, each color space has a place in defining the endless array of colors in a particular field or industry. Some color spaces weight one parameter to describe the luminance or “lightness” of a color, while the other parameters capture the hue.
Other color spaces use a single parameter to describe one key quality of an emissive light source, like how it compares to an old fashioned tungsten wire bulb, or how well it “brings out” color in other objects.
Why Use a Spectrometer to Measure Color?
More information. More flexibility. In fact, it seems a little odd not to use a spectrometer to measure color, but it is actually common practice.
Simple color meters use red, green and blue filters in combination with diodes or sensor pixels for measurement. More advanced systems use tristimulus filters that mimic the CIE color matching functions. These work well for incandescent light sources, but are less accurate for LEDs. Handheld color meters may measure up to 20 wavelength bands, but this is not enough for research or high-accuracy measurements.
To detect small color changes, very high color resolution is necessary. By capturing the complete spectrum, the color measurement made by a spectrometer allows careful and detailed analysis of data. Color meters and analyzers based on filters or detection over specific bands simply leave a lot of information on the table – information that can be used to better inform the color measurement.
Some color analyzers are also strongly dependent on lighting conditions, since objects tend to appear different colors under different illumination. With the right lighting, two objects can appear to be identical in color even if the reflected spectral power distributions differ, an effect called metamerism. If the lighting changes, however, the colors can look significantly different. This makes controlled lighting conditions essential to consistent results.
When color measurements are made with a spectrometer, a full reflected or emissive spectrum is the starting point for all calculations. That allows the data to be analyzed in different ways, and even recalculated at a later date to change the observer, the illuminant, or the color space. It offers maximum flexibility with the same high accuracy as if the calculation had been performed that way initially.
Featured Products for Emissive Color Measurement:
|TORUS-25-OSF||Torus spectrometer (360-825 nm) has low stray light and high thermal stability. This version includes a 25 µm slit and order-sorting filter, but your choice of optical bench accessories very much depends on the LED wavelengths you are measuring.|
|FOIS-1||Integrating sphere that collects light from emission sources such as LEDs|
|LED-PS||Power supply powers the LED, displays the LED drive current and holds the LED in place|
|QP400-2-VIS-NIR||Premium-grade patch cord directs light collected at integrating sphere to the spectrometer|
|HL-3-INT-CAL||Radiometrically calibrated light source designed for use with an integrating sphere|
Featured Products for Color Measurement:
|TORUS-50||Holographic concave diffraction grating spectrometer (360-825 nm) with 50 µm entrance slit|
|HL-2000||Tungsten halogen light source (360-2400 nm)|
|QR400-7-VIS-NIR||Reflection probe (6-around-1 fiber design), optimized for VIS-NIR response, 2 m length|
|RPH-1||Fixture for holding 1/4″ (6.35 mm) diameter reflection probes|
|WS-1-SL||Diffuse reflectance standard has 99% reflectivity from 400-1500 nm|