How Does a Spectrophotometer Work?

The basic way a spectrophotometer functions is based on the absorption of photons. Higher amounts of photons correspond to higher intensities of light.

You may remember from chemistry class that light is a form of electromagnetic radiation, like microwaves and gamma rays. When we talk about the spectrum of light, we’re talking about a spectrum of energy, where different energy levels create what we perceive as different colors. The colors of the rainbow follow the progression of energy, with red being the lowest and violet being the highest.

In terms of substances, a sample that absorbs all visible light and doesn’t reflect anything appears black, while a substance that does the opposite looks white. In between those two are substances that reflect certain energies of light and absorb others, displaying specific colors.

Returning to our spectrophotometer, this tool is basically a calibrated light counter.

• “Spectro” refers to the fact that light is dispersed into individual or groups of wavelengths in the electromagnetic spectrum of energy. Some of that energy is in the ultraviolet and visible light range, which certain spectrophotometers can read, while others can measure infrared radiation. A typical spectrophotometer can measure 31 wavelength bands of light across a 300nm-wide range. More expensive instruments can measure more than 150 bands of light across an 800nm-wide range.
• “Photometer” in the name refers to the ability to measure the intensity of light at each group of wavelengths and scale it to a range of human perception from 0-100. Zero equals total darkness and 100 is perfect white. Some properties, like fluorescence, make it possible for this scale to go over 100, so most spectrophotometers can reach 150 or 200.

By combining these two tools, we can generate specific data about the released colors and associated wavelengths to inform various applications.