ATP testing is a simple and affordable test method which verifies cleaning effectiveness in seconds. The science is based on the detection of organic residues on surfaces and in water samples using a bioluminescent reaction. Pen-shaped test devices contain a modified firefly enzyme that reacts with organic material to produce light, which is then measured in a handheld meter (called a luminometer).

The luminometer converts the light output into an RLU number (Relative Light Unit): the lower that number, the cleaner the surface (or less contamination in the water sample if a CIP system is being tested).