RLU

RLU stands for Relative Light Unit, a measure used to quantify luminescence in biological and biochemical assays. It is a non-absolute, instrument-dependent value representing the intensity of light detected by a luminometer. RLUs are used to express how much light a sample emits, with higher values indicating greater luminescence, but they do not constitute a standardized physical unit.

Measurement and interpretation depend on several factors. The reading is influenced by instrument settings such as integration time and sensitivity, plate type, substrate concentration, enzyme activity, and sample volume. Because RLUs reflect assay conditions, they are often considered relative to a control rather than an absolute signal. Background luminescence from wells or reagents is typically subtracted to improve accuracy, and results are frequently normalized to negative or positive controls.

Common applications include luciferase reporter assays, where luminescence correlates with gene expression or promoter activity, and various enzyme activity or viability assays that use luminescent substrates. In high-throughput screening, RLUs enable rapid comparison across thousands of samples.

Data handling and reporting practices emphasize transparency about assay conditions. Since RLUs are arbitrary, results are usually presented as fold change relative to a control or as normalized values per cell or protein content. It is important to specify the instrument model, integration time, substrate used, and any normalization steps to allow meaningful comparisons across experiments.

See also: luminescence assays, luciferase, luminometer, normalization.