Relative Light Units (RLU)
measurementThe numerical unit used to report ATP test results, based on the amount of light produced during the ATP reaction.
Definition
Relative Light Units (RLU) are the output of an ATP luminometer. Higher detectable ATP produces more light, and therefore a higher RLU reading. RLU values are not standardised across instruments—each ATP system has its own scale, so results should only be interpreted against thresholds validated for that specific system.
Why it matters
Misreading RLU values as universal or comparable across brands is a common source of error in hygiene monitoring programmes. Correct interpretation depends on establishing pass, caution and fail thresholds for the system in use.
Practical applications
RLU thresholds are used in food, healthcare and hospitality hygiene programmes to trigger recleaning, staff coaching or root-cause investigation.
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