Lambda is the 11th letter of the Greek alphabet, and throughout history, it has been represented on everything from Spartan battle shields to sorority sweatshirts. When it is used in the equation for lambda max, or λmax, it identifies which wavelengths achieve maximum absorption.

Sometimes, chemists and biologists must test substances to see how much light or energy they absorb. The different levels of absorption are calculated along a spectrum of wavelengths. Lambda max refers to the wavelength along the absorption spectrum where a substance has its strongest photon absorption. Scientists can then use lambda max as a parameter to compare the different qualities of all types of molecules and substances.

Thanks to its high degree of accuracy, lambda max is often applied to the practice of UV-visible spectrophotometry. With an instrument called a UV/Vis spectrophotometer, scientists can measure the intensity of a beam of light both before and during its passage through a substance.

Traditionally, such an instrument is used to determine the relationship between a wavelength and color. When a beam of light passes through a solution with color, it absorbs some of that light. The amount absorbed determines which color you see when you look at the solution. That’s because the apparent color of an object is determined by the wavelengths of the photons of light from that object that reach your eyes. If a substance does not absorb any light, the solution appears colorless.

Understanding how much light a substance absorbs can be important in many scientific fields, including materials science, chemistry, physics and molecular biology. It’s especially important in many biochemical experiments. Often, scientists have to look at samples including proteins, DNA, RNA and bacterial cells to see how they react to colored compounds. This is important because some of the modern pharmaceutical solutions that you ingest have colored compounds such as dyes in them.

Before those medicines hit the market, scientists use a spectrophotometer and the lambda max equation to figure out how even the tiniest cells in your body might react to the compounds in the drug. They can detect any impurities in a substance and determine how much of that substance your body can safely consume. In this way, an understanding of lambda max helps biochemists to know how much Tylenol you can take to say goodbye to a headache without harming your body in any way.