You have acquired a more efficient appliance and are looking forward to lower consumption. At the same time it is now used more often or for longer because its operation is perceived as economical. That need not be a personal fault. However, these are two different changes that you should distinguish in your expectation of the savings.
Efficiency and extent of use are different quantities
The Umweltbundesamt describes the rebound effect as a feedback of efficiency gains on behaviour: if usage costs fall, more frequent or more intensive use can offset part of the expected saving. [REBOUND] This general explanation does not yet say how large the effect is for a particular household.
In the fictional example a household replaces light sources and then consciously expands the lighting to additional areas. The newly lit surfaces are an additional benefit. Anyone who then compares total electricity consumption with earlier consumption should not overlook this change. A product specification for individual light sources alone does not answer the question about the overall effect of the new concept.
Name the desired benefit before purchase
Note what you want to achieve with the change: the same purpose with less energy, additional comfort, or both. That way you can later assess whether an increase in consumption stems from different use or whether a technical question remains open.
Avoid hasty diagnoses. If consumption does not fall as expected, rebound is only one possible consideration and not proof of the cause. Other changes in the household and the basis of comparison must also be taken into account. The article does not evaluate a real measurement series.
Make a simple usage agreement
Discuss which new use is actually desired and what has been added only out of habit. An appropriate switch-on or switch-off routine can be an organisational decision in its own right. Technically required operating times, device specifications and personal needs are not overridden by this. Shutdowns of unfamiliar systems are not recommended here.
If several people use the appliance, the purpose should be understandable. “It uses little” is not a sufficient common goal if no one knows whether it will be needed permanently. A clear agreement can do without household monitoring and without minute-accurate control.
Label the comparison honestly
When reviewing later, record whether the extent, duration or number of devices has changed. Distinguish the technical product specification from the actually observed household result. Do not use a general rebound percentage as a personal correction to your calculation.
The 2019 source here serves for the basic definition of the term. The text does not use the estimate ranges given there as a current value for Austria or Germany. The decision question is the same in both countries: which benefit do I want to buy additionally, and what saving can I expect at all under this changed use? A conscious comfort decision can be legitimate; it should simply not be accidentally counted as unchanged use.