1. Typical linear ranges
- Most bench-top luminometers have a linear dynamic range of 3–5 orders of magnitude (10³–10⁵ RLU to 10⁶–10⁹ RLU).
- High-sensitivity luminometers or microplate readers may have broader linear ranges, sometimes up to 7 orders of magnitude.
- Exact values depend on:
- Detector type (photomultiplier tube, PMT)
- Gain settings
- Integration time
- Substrate and assay conditions
2. How to determine linear range experimentally
- Prepare a serial dilution of a luciferase standard or your sample (e.g., 1×, 0.5×, 0.25×, 0.125×).
- Measure RLU for each dilution.
- Plot RLU vs. enzyme concentration.
- The linear portion of the curve is the usable range. Any plateau indicates detector saturation; any flattening at low RLU indicates signal noise.
3. Practical notes
- Substrate limitation: Even if the detector is linear, very high enzyme activity may deplete substrate, causing apparent nonlinearity.
- Integration time: Longer readings increase total RLU but can push the detector into saturation.
- Instrument documentation: Always check your luminometer’s user manual for recommended RLU limits and linear range.