Seeing the Light: Understanding Visible UV/VIS Spectrophotometers

spectrophotometersThe Jenway 74 Series Spectrophotometer with CPLive™ Connectivity allows you to upload results and protocols safely and securely to the cloud, share data with colleagues, and simultaneously manage multiple devices through the CPLive app on your computer, tablet, or smartphone.

What is Spectroscopy?

Spectroscopy is the study of how materials react to radiated energy. Light is a radiated energy. Many spectrometers utilize light as the radiated energy source. “Light” exceeds the visible spectrum of color the human eye can see.  Visible/white light breaks down into separate and unique colors: red, orange, yellow, green, blue, indigo and violet. These colors, and what the human eye can see, are a very small and limited range of the electromagnetic spectrum of radiated energies.

When visible light shines on a blue shirt, the dye in the shirt reflects the blue light and absorbs all the other colors we can see. This is a simple example of how a material, such as a shirt, reacts to light. Over time, the dye may wash out and its concentration in the fabric lessens. The loss in dye concentration can be seen as the color appears lighter and lighter. If looking at the shirt using a spectrometer set to the blue wavelength range, the transmittance (the transmission of radiant energy) would be increasing, and the absorbance (light-absorbing ability) decreasing. The law that surrounds spectroscopy is called “Beer’s Law” written commonly as

A = ε l c

“A” stands for absorbance, “ε;” for Molar absorptivity (also known as the extinction coefficient), “l” represents the pathlength, and “c” is concentration

All spectrometers are based on this law in one way or another. Given the equation, absorption is directly correlated to the extinction coefficient, pathlength, and concentration. If any of the variable on the right-hand side of the equation increases, absorbance will also increase.

Visible and Ultraviolet-Visible (UV-VIS Spectrometers)

As the name implies, the radiated energy source for these spectrometers is either visible light or both visible and ultraviolet light. A visible spectrophotometer measures the absorption level of one monochromatic visible frequency at a time and then sums up those individual absorption levels to draw a spectrum. An ultra-violet visible spectrometer uses the second lamp, usually deuterium, to measure light from 190 nm to 1100 nm.

Read the article, Seeing the Light: An Overview of Visible and UV-VIS Spectroscopy, to learn more.

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