What Do Spectrophotometers Measure?
A spectrophotometer is an instrument that measures color by shining a beam of light and capturing the amount of light that reflects back or transmits through to quantify color. Spectrophotometers can provide color data for just about any sample, including liquids, plastics, paper, metal, fabric, and painted samples.
Where are Spectrophotometers Used?
Spectrophotometers are used in every industry that requires accurate color. From packaging to textiles to beverages and plastic parts, these devices help ensure the color being produced matches the color that was originally specified.
How Does a Spectrophotometer Measure Units of Color?
Using a light source, a spectrophotometer can accurately detect color reflectance or light transmittance for quantitative analysis.
Every physical sample has its own reflectance (the amount of light it reflects), and transmittance (light absorption). A spectrophotometer measures a sample’s reflected or transmitted light to capture its fingerprint and determine the amount of light reflected or transmitted from the visible ranges of the different portions of the visible spectrum.
What’s the Difference between a Reflectance and a Transmission Spectrophotometer?
Solid samples can absorb or reflect light. To measure a solid object, a reflectance spectrophotometer shines a light beam onto the surface and a detector measures the amount of light intensity that reflects back from specific wavelengths of the visible spectrum. This is called a reflectance measurement and is typically achieved within the instrument using a spinning filter wheel of specially designed colors or a diffraction grating. The resulting measurement is the sample’s reflectance curve with a varying wavelength from around 400 to 700 nanometers.
For instance, a sample that absorbs light over all visible ranges and transmits none of visible wavelengths appears black. If all visible wavelengths are transmitted (the sample absorbs nothing), the sample will appear white. If a sample absorbs red light (around 700 nm), it will appear green because green is the complementary color of red.
Translucent samples like plastic film and clear liquid sample solutions allow light to pass through. To measure a translucent sample, a transmission spectrophotometer transmits light through the sample and measures how much light passes through across the visible spectrum.
What is a UV Spectrophotometer?
In addition to measuring the transmission or reflectance of visible light, a UV visible spectrophotometer with calibrated UV light can also measure color in the component wavelengths of the ultraviolet range (185 - 400 nm) and visible range (400 - 700 nm) of the electromagnetic radiation spectrum.
What is a Spectral Reflectance Curve?
Using a spectrophotometer, you can measure an object to see how much light is reflecting at each point across the visible spectrum. Think of this color measurement like a fingerprint that is unique to that sample. The resulting reflectance data is that color’s “fingerprint,” and can be used to create a reflectance curve. The reflectance curves two samples can be compared to to see if they are a match and identify metameric issues.
What is a Metameric Pair?
Metameric pairs are shades that appear to be identical under a single specified lighting condition but have different fingerprints.
This graph shows the reflectance curves for two reds. Both curves strongly absorb blues, both absorb greens in moderation, and both are strong reflectors of reds. Notice the curves twist over each other. Whenever two physical samples have curves that cross at least three times, they are a metameric pair. When objects are a metameric pair, metamerism is apparent. Although they will sometimes appear to be the same color, they will not match under all lighting conditions.
What are the Different Types of Spectrophotometers?
If all samples were flat, opaque, or the same thickness, one instrument would work for all industries. However, samples can be curved, transparent, metallic, textured, or more. When choosing a spectrophotometer, it’s important to find one that will meet your needs based on what you’re measuring.
0:45/45:0 Spectrophotometers
One of the most common types of spectrophotometer, this measurement geometry emits light at 45 degrees to the sample surface and measures light reflected at a fixed angle to the sample, 0 degrees. This type of measurement excludes gloss to most closely replicate how the human eye sees color and is commonly used for measuring color on flat, smooth, or matte surfaces.
Sphere Spectrophotometers
Spherical instruments capture light reflected from all angles of a sample. This measurement type can include or exclude the surface appearance of your sample. These devices are commonly used for measuring color that has been applied to textured surfaces such as textiles, carpets and plastics, as well as glossy or mirror-like surfaces, including metallic inks and foil printing.
Multi-Angle Spectrophotometers
Multi-angle instruments view the color of a sample as if it is being rotated back and forth, just as you would twist a sample to see the color at various angles. Today’s multi-angle instruments are typically used for specialty coated pigments and special effect colors with additives, such as nail polish and automotive coatings.
Single Beam vs. Double Beam Spectrophotometers
Spectrophotometers come in both single and double beam configurations. A double beam spectrophotometer compares the light intensity between two light paths, one path containing a reference sample and the other the test sample. Single beam spectrophotometers measure the relative light intensity of the beam before and after a test sample is inserted.
What Does a Spectrometer Measure?
Spectrophotometry captures and measures colors in a wide variety of materials and is available in liquid and paper. Spectral spectrometry is also a device used in detecting specific frequencies in electromagnetic spectrum. Spectral spectroscopy devices are based on these instruments.
Where to Learn More about Spectrophotometers
We offer an extensive resource library that contains whitepapers, case studies, on-demand webinars, online training courses, and more to learn about a variety color measurement topics. You can also contact one of our Color Experts for help.
