Measurement notes
Sum activity separately across the light and dark phases over several stable days and take the ratio or the dark-phase percentage. Normal nocturnal mice concentrate the large majority of activity in the dark phase.
Endpoint methods library
Circadian & activity rhythm endpoint
Day/night activity ratio
Proportion of total activity occurring in the dark versus light phase, a simple index of how well behavior is partitioned by the clock.
Unit
ratio or percent
Readout
Dark-phase activity divided by light-phase activity (or percent of activity in the dark)
Assays
Home-cage video, beam-break, wheel under LD
Decision summary
Use the day/night activity ratio as a quick, intuitive check that a nocturnal animal is concentrating activity in the dark phase. It is only defined under a light-dark cycle and is best read as a coarse partitioning index, not a substitute for amplitude or period.
| Primary value | Dark-phase activity divided by light-phase activity (or percent of activity in the dark) |
|---|---|
| Common units | Ratio (e.g. 4:1) or percent in dark |
| Compatible assays | Home-cage video, beam-break, wheel under LD |
| Required boundary | Light-dark schedule and bin size |
| Do not infer alone | Period, endogenous phase, or rhythm robustness |
Interpretation limit
Because it is defined relative to the external light-dark cycle, the ratio measures masking plus entrainment, not the endogenous clock. A flattened ratio signals disruption but cannot distinguish a mistimed clock from a weak one or from simple light masking.
Data capture
Store animal ID, light-dark schedule, days summed, light and dark activity totals, ratio, and activity measure.
Confound checks
- Direct light masking inflating apparent dark preference.
- Scheduled feeding or husbandry shifting activity into the light phase.
- Strain and age differences in nocturnality.
- Wheel access amplifying dark-phase activity.
Reporting checklist
- Light-dark schedule and number of days summed.
- Whether ratio or dark-phase percent is reported.
- Bin size and activity measure.
- Exclusion of disturbed days.
References
Evidence notes
Endpoint pages should cite the method literature behind the scored value and keep high-specificity protocol claims qualified unless the source supports them.
- Jud C et al. A guideline for analyzing circadian wheel-running behavior in rodents under different lighting conditions. Biol Proced Online. 2005. doi:10.1251/bpo109.
- Refinetti R, Cornélissen G, Halberg F. Procedures for numerical analysis of circadian rhythms. Biol Rhythm Res. 2007. doi:10.1080/09291010600903692.
Related workflow paths
Endpoint articles link to adjacent products, software workflows, and sibling endpoints where the connection is useful and already routable.
